ALBERT

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Occurrence of gas-extraction-induced earthquakes in the Groningen Province of the Netherlands raised the need for dynamic performance assessments of the regional flood defence system, consisting of an extended levee network. The soils underlying parts of the levees comprise Holocene tidal deposits, susceptible to liquefaction and cyclic strain softening. This paper describes the numerical methodology adopted to evaluate the seismic performance of such important flood protection structures, including: (1) the development of ground motions consistent with regional seismic hazard, (2) two dimensional, effective-stress, dynamic numerical simulations of levees, (3) use of calibrated advanced constitutive models to simulate complex soil behavior, (4) estimation of post-seismic deformations, and (5) validation against centrifuge experiments. The application of this methodology captured the important mechanisms governing these types of problems, resulted in an improved characterization of system behavior and allowed for a more rational and reliable prediction of levee performance.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The majority of houses in the Groningen gas field region, the largest in Europe, consist of unreinforced masonry material. Because of their particular characteristics (cavity walls of different material, large openings, limited bearing walls in one direction, etc.) these houses are exceptionally vulnerable to shallow induced earthquakes, frequently occurring in the region during the last decade. Raised by the damage incurred in the Groningen buildings due to induced earthquakes, the question whether the small and sometimes invisible plastic deformations prior to a major earthquake affect the overall final response becomes of high importance as its answer is associated with legal liability and consequences due to the damage-claim procedures employed in the region. This paper presents, for the first time, evidence of cumulative damage from available experimental and numerical data reported in the literature. Furthermore, the available modelling tools are scrutinized in terms of their pros and cons in modelling cumulative damage in masonry. Results of full-scale shake-table tests, cyclic wall tests, complex 3D nonlinear time-history analyses, single degree of freedom (SDOF) analyses and finally wall element analyses under periodic dynamic loading have been used for better explaining the phenomenon. It was concluded that a user intervention is needed for most of the SDOF modelling tools if cumulative damage is to be modelled. Furthermore, the results of the cumulative damage in SDOF models are sensitive to the degradation parameters, which require calibration against experimental data. The overall results of numerical models, such as SDOF residual displacement or floor lateral displacements, may be misleading in understanding the damage accumulation. On the other hand, detailed discrete-element modelling is found to be computationally expensive but more consistent in terms of providing insights in real damage accumulation.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Groningen gas field, which is being exploited for more than five decades, has been experiencing shallow and small magnitude earthquakes that cause limited structural damage to the building inventory in the region. These earthquakes are recorded in a relatively small area with multiple recording networks, which constitute a dense strong ground motion sensor grid, providing valuable insight into the characteristics of the motions produced by some 2500+ small faults at 3 km depth. The particularities of the Groningen soil, as well as the high seismic vulnerability of the structural inventory, render the Groningen earthquake problem complex, although the magnitudes experienced so far did not exceed 3.6M〈sub〉L〈/sub〉. This paper is an attempt to compare the Groningen earthquake records to records from other induced seismicity and natural seismic events with similar characteristics in terms of magnitude, epicentral distance and depth, for identifying systematic differences in terms of component-to-component variability. In order to achieve that, a total of 1831 recording suites (i.e. couples of horizontal components) are used. 201 of these are Groningen records, 1112 are from other induced seismicity events to geothermal, waste water injection and hydraulic fracturing activities, while 517 are from natural earthquakes. The high polarity of the Groningen records, that is previously reported in the literature and represented as component-to-component variability in risk models, is the main focus of this paper. The component-to-component variability constitutes an important step when implementing ground motion models (GMMs) in risk assessment studies. In this study, in agreement with previous research, the component-to-component variances show that the Groningen induced seismicity events present stronger polarity than the other records used for comparison. The other induced seismicity recordings also show high component-to-component variances as compared to the natural events records, but the main difference is that their variances start decreasing in medium-to-long (i.e. above 0.6 s) periods while the variances steadily increase in the case of Groningen records. Furthermore, it is also observed that the component-to-component variances increase considerably when the rotated-to-max-PGA angle, explained in the paper, is used for defining the two horizontal components instead of using components as-recorded or rotated perpendicular to the station back azimuth. A modification to the component-to-component variance model of Groningen GMM v5 has also been proposed in this study for taking into account the orientation of the structural plan directions in respect to the ground motion component directions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Natural gas production in the Groningen field in the Netherlands is causing induced earthquakes that have raised concerns regarding the safety of the local population given that the exposed building stock (which is predominantly unreinforced masonry residential housing) has not been designed and constructed considering seismic loading. Significant effort has been invested to date in assessing the safety risk of these buildings within a probabilistic framework. This paper describes the efforts that have since been made to extend this framework for probabilistic damage assessment of the buildings, for slight non-structural, slight structural and moderate structural damage. Fragility functions for non-structural damage have been developed considering the observed damage from damage reports, rather than from damage claims due to a number of issues with the latter, as described herein. Structural damage has been estimated using analytical models that have been calibrated through extensive in situ data collection and experimental testing. The probabilistic damage assessment is presented in terms of F-N curves, which plot the annual frequency of exceedance against number of buildings reaching each damage state.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The exploitation of geo-resources in the northern part of the Netherlands (Groningen region) is triggering shallow earthquakes, rising the need of assessing the current building stock. Being the region not prone to tectonic earthquakes, buildings are designed as wind-resistant systems and have specific characteristics that can limit their seismic performance. In this framework, an extensive research has been carried out on the performance of low-rise unreinforced masonry (URM) buildings at Delft University of Technology. Major attention was focussed on the behaviour of terraced houses, which represent the majority of structures within the URM building stock. In this paper, the case study of a modern Dutch terraced house, built after 1980, made of calcium silicate element masonry and reinforced concrete floors is considered. A quasi-static cyclic test on a full-scale two-storey structure resembling the considered typology is presented. The experimental results are used to evaluate the seismic performance of the structure in the framework of the nonlinear static analyses. A comparative study highlights the importance of the selection of the assessment procedures. Adopting the experimental results as a benchmark, a blind prediction contest revealed a large output variability depending on the adopted analysis method and modelling choices. Consequently, the cross-validation among different analysis methods currently appears the best approach to achieve a more accurate prediction of the structural capacity. The combined experimental and numerical work presented in this paper allows gaining a deeper insight on the evaluation of the seismic performance of Dutch terraced houses.〈/p〉

Beschreibung: 〈p〉This erratum is published due to Retrospective Open Access requested by author.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper presents a simplified procedure for the evaluation of the free-field consolidation settlement induced by liquefaction, using the results of 1D site response analysis in effective stress and a simplified approach based on empirical chart. The excess pore water pressures induced by the seismic action are generated by both a simple stress-based model implemented on a non-linear dynamic analysis and a simplified relationship between the safety factor against liquefaction and the excess pore pressure. The post-cyclic settlement is finally calculated on the obtained distribution of excess pore water pressure along the soil column. The proposed method has been used to estimate the consolidation settlements in a centrifuge test and in well-documented case histories of widespread liquefaction: Treasure Island and Marina District after the 1989 Loma Prieta earthquake. The results have been compared to the measured settlements and to the values obtained by previous studies. It is shown that the proposed approach leads to a much more accurate estimate of the post-liquefaction consolidation settlement, with just a little increase of the calculation effort.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In concentrically braced frames, braces-to-adjacent member connections are suitable locations for the dissipation of seismic energy. If the implementation of dissipative connections does not compromise the global lateral stiffness of the structure, the compression braces can then be protected from buckling, while the structural ductility is increased and the action effects reduced. Furthermore, an efficient use of dissipative connections allows reducing the cost of post-earthquake interventions. In this paper, an innovative dissipative connection for braced frames is proposed, consisting of a steel plate bent to a U shape and connecting the brace to the adjacent column. In this connection, energy dissipation is obtained through the inelastic flexural deformation that takes place in the plate. This paper presents experimental results on the isolated U-connection and on single-storey concentrically braced frame (real scale) including the U-connection. Besides considering several variations on the geometry of the U-shape plate, the tests considered both monotonic and cyclic loading. The results highlight the efficiency of the U-connection to dissipate the energy input through inelastic deformations. On the other hand, the cyclic tests show however that the connection is potentially sensitive to fatigue, as the deformation capacity is significantly reduced with repeated loading and increasing stress amplitude, requiring thus specific attention in practical design situations.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In the present study, the lateral response of systems including the “soil-embedded rocking foundation-SDOF superstructure” system was reported under slow horizontal cyclic loading tested in the 1 g condition. Accordingly, the effects of variation in the foundation embedment depth and superstructure slenderness ratio on the lateral performance of the systems were investigated. Based on the experimental results, the embedded rocking foundations could limit the moment transferred to the superstructure. However, the over-strength was apparent in the nonlinear performance. Moreover, it was evident that for the 1 g modelling, the increase in foundation embedment depth increased the difference between maximum experienced moment and the theoretical ultimate moment capacity attained from the existing theories. In addition, the stiffness ratio of embedded to shallow foundation was explored and compared to the theoretical expressions existing in the literature. Also, by concentrating on the energy dissipation of systems, the contribution of rocking and sliding mechanisms to the foundation lateral response was evaluated. With the increase in the foundation embedment depth, the contribution of sliding mechanism was significantly reduced, especially for the lower slenderness ratios. Finally, the influence of foundation embedment depth on the pinching index of behavioral response was discussed.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper presents the results of centrifuge model tests conducted on piled raft foundations in liquefiable soils to investigate the performance of drainage techniques as a liquefaction countermeasure method. Two series of centrifuge tests were conducted on 2 × 2 end-bearing piled raft foundations with and without drainage wells in multilayer soil deposits. The results indicate that the drainage well systems significantly reduce the foundation settlement, the excess pore water pressure ratio, and the time of dissipation under seismic loading by providing shortened water flow paths. Variations of the acceleration response, bending moment, and axial force of the piled raft are shown to be dependent on the type of surface layer. In Test-1-E with the liquefiable surface layer, the acceleration response, bending moment, and axial force of the piled raft with drainage systems were significantly larger than those observed in the piled raft without drainage systems during shaking. In contrary, in Test-2-E including a non-liquefiable surface layer, bending moment and axial force of piled raft in the absence of drainage wells were larger than those of the piled raft system with drainage wells. However, the acceleration response of raft in both systems was almost the same during shaking. The recorded data of the piled raft systems with/without vertical drains and the surface gravel layer (as a horizontal drainage system) are compared in details.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This study proposes a response-based parameter for strong motion duration which is computed for structures and is the total time they are nonlinear during an earthquake. Correlation between structural response and duration for structures, subjected to a set of spectrum matched ground motions, is employed to examine the efficiency of the proposed method. The spectral matching procedure ensures that the influence of amplitude and frequency content of motions on structural response variability is significantly removed. Four concrete building type systems are studied and correlation coefficients of structural response with the proposed duration definition are examined. Comparison of the proposed method with other existing definitions—the record-based and response-based metrics—shows about 15–20% improvement in the correlation values.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Several techniques have been developed in order to mitigate damage to buildings during and after liquefaction events. Benefits of using vertical drains have been verified by analysing their performance in the soil and evaluating their effectiveness in dissipation of excess pore pressures generated by the earthquake. However, the effect of drains in the soil below structures requires further investigation. In this paper, a dynamic centrifuge test series was carried out to evaluate the performance of a vertical drains arrangement below shallow foundations. High permeable rubble brick was used as coarse material inside the drains to provide positive results not only from a geotechnical point of view but also from an environmental and sustainable perspective. The behaviour of drains was analysed when they are located under shallow foundations of a building, in terms of the excess pore pressures generated during the earthquake and subsequent post-seismic dissipation, the foundation settlement and its dynamic response.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The present work investigates the effect of soil–structure interaction (SSI) on foundation motion recorded at accelerometric stations installed at the lowest level of buildings. For this purpose, two sites of instrumented buildings, for which foundation and free-field strong motion recordings are available, are studied in terms of transfer functions as well as strong motion intensity and frequency content. The importance of such an instrumentation scheme is highlighted, especially when it comes to assessing the filtering action of the foundation on moderate to high frequency components of free-field motions. The effect of ground motion filtering at the soil–foundation interface is further quantified in terms of amplitude and frequency content. The recordings are supplemented by a parametric analysis of the sub-structured soil–structure system leading to regression expressions that associate the intensity and frequency parameters of the recordings obtained at the base of the instrumented buildings and the corresponding free-field ones. It is shown that kinematic and inertial decoupling of SSI is not only a useful but also a necessary task for correcting earthquake records obtained at building basements particularly for high frequency-dominated ground motions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The potential for utilizing high proportion recycled aggregates sourced from low strength waste concrete in new concrete construction is investigated in this paper. A comprehensive experimental program, consisting of ten full-scale, flexure critical reinforced concrete columns, five of which were constructed of natural concrete aggregate and five of which contained approximately 50% recycled concrete aggregate replacing the mid-sized coarse natural aggregate, was conducted to determine the effects of different axial loads and different spacings of transverse reinforcement on the seismic characteristics of columns incorporating recycled concrete aggregates. Seismic characteristics were quantified by analysis of hysteretic response, energy dissipation capacities, damage progression, residual displacement, and strain distribution of the longitudinal reinforcement. The test results indicate that the reinforced concrete columns constructed of natural aggregate concrete and those constructed of recycled aggregate concrete exhibit similar seismic performance, despite the fact that the compressive strength of the recycled aggregate concrete was slightly lower than that of the natural aggregate concrete. A theoretical study was then conducted to predict the load–displacement response of the columns. The comparison of the experimental data with the results of these theoretical calculations indicated that conventional RC design theory applied to columns incorporating natural aggregate is also valid for columns incorporating recycled aggregate. Finally, the confinement effect of the transverse reinforcement in columns subjected to low axial load were also critically evaluated for columns built with recycled aggregate concrete.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Substructure hybrid simulation test (SHST) is a novel seismic experimental method for analyzing structures, which usually divides the global structure into two components: the experimental substructure and the numerical substructure. An SHST system based on the OpenFresco platform was established. To ensure the high accuracy of the numerical substructure in SHST, a finite element model that corresponded to a quasi-static experimental investigation on high-strength steel composite K-shaped eccentrically braced frame (K-HSS-EBF) was established and analyzed using OpenSees. A three-story and five-span spatial K-HSS-EBF was used as the prototype and the three-story steel frame with a K-eccentric brace on the left second span was taken as the experimental substructure. The remaining four-span was modeled as a numerical substructure in OpenSees. SHST was performed with a half-scale hybrid simulation model. According to the test results, the displacement loading precision of the experimental substructure was analyzed. In addition, the shear link rotations of the experimental and numerical substructures were compared. The time curve of the displacement and the base shear of the hybrid simulation model were also compared with the simulation results of the global numerical model. The results revealed that the seismic response characteristics of the K-HSS-EBF were successfully recaptured using the numerical substructure model established in OpenSees and the spatial SHST system based on OpenFresco.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In recent years, much of the research in geotechnical earthquake engineering has focused on liquefaction of loose, saturated sands and silts. However, the dynamic behaviour of soft, clayey soils and their interaction with pile foundations during the earthquakes have received relatively little attention. In this study, an attempt is made to investigate the dynamic behaviour of soft clay and its interaction with pile foundations during earthquakes using high gravity centrifuge testing. A model single pile and two sets of 3 × 1 row model pile groups with different pile spacing were embedded in soft kaolin clay and tested under the action of model earthquakes at 50 times the earth’s gravity. The strength and stiffness of clay were evaluated using a T-bar test and an air hammer device respectively. The focus of this research is to investigate the dynamic response of friction piles in soft clay. However, this depends on the dynamic response of the soft clay layer around the pile. To this end, one-dimensional ground response analysis was performed using DEEPSOIL software to emphasise the importance of non-linear analysis in characterising the seismic behaviour of soft clays. It will be shown that clay response depends both on the earthquake intensity and the shear strength and stiffness of the clay layer. This has a direct bearing on the response of single piles and pile groups, with larger amplification occurring for small intensity earthquakes and attenuation occurring for stronger earthquakes.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉During the Nepal Gorkha Mw7.8 earthquake, the two-storey stone masonry buildings experienced the most severe damage among all structural types in the seismically affected areas. However, this type of construction will continue to be used in the vast areas of the Himalayan belt due to the less developed economies and limited access to cement and steel. The experimental verification of different reinforcement techniques applicable in these areas is urgently needed. In this paper, three scaled two-storey stone masonry houses with timber floors were tested on a shake table under various seismic scenarios to verify the effects of reinforcement techniques using timber laces and gabion wires. The seismic performances of the models with and without reinforcement were evaluated and compared through crack pattern development, the structural damage and failure modes, and the changes in dynamic characteristics. The experimental results are presented, analysed and discussed. The un-reinforced two-storey model completely failed at a PGA of 0.4 g; while the model strengthened with timber laces experienced only local failure at a PGA of 0.51 g, and the reinforced model using both timber laces and gabion wires remained intact with limited damage at a PGA of 0.92 g. This research confirmed that the seismic performance of two-storey stone masonry structures could be substantially improved when inexpensive and easy-to-implement reinforcement techniques using local materials were utilized. 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Risk assessment and management is an important step towards resilient and sustainable cities. Among many other perils, both natural and manmade, seismic risk is a major threat for resilience and sustainability. In recent decades, several methods for seismic risk assessment have been proposed, including the well-known Vulnerability Index Method (VIM). In this study, a probabilistic version of the VIM, which we call the Vulnerability Index Method-Probabilistic (VIM_P), is proposed. The VIM_P requires essential information on the seismic hazard and on the vulnerability of the building stock. Seismic hazard is determined using the exceedance rates of macroseismic intensities, as defined in the European Macroseismic Scale (EMS). Seismic vulnerability is defined by means of vulnerability probability density functions (〈em〉pdf〈/em〉) that describe the probability distribution of the corresponding vulnerability index. Beta-like functions are used for these 〈em〉pdfs〈/em〉. VIM_P quantifies seismic vulnerability by means of three vulnerability curves, 〈em〉Lower〈/em〉, 〈em〉Best〈/em〉 and 〈em〉Upper〈/em〉, according to the quantity and quality of available information, thus allowing three estimates of seismic vulnerability and risk. Then, seismic risk is computed via the convolution of seismic hazard and seismic vulnerability, considering semi-empirical damage functions. Seismic risk is given through the exceedance frequencies of the damage grades. To highlight the capabilities of the VIM_P, the seismic risk of about 70,000 residential buildings in Barcelona was assessed. According to the results, the exceedance frequency of the collapse damage state for more than the 50% of the buildings in the 〈em〉Eixample〈/em〉 district would be greater than 1 × 10〈sup〉−5〈/sup〉. This confirms the relatively high seismic risk in the city, mainly due to the high vulnerability of the built environment. Specific software, USERISK20015, has been developed for routine applications of VIM_P. It is hoped that VIM_P and this new tool for seismic risk assessment will be useful to stakeholders and civil protection authorities for risk management and prioritizing actions that can help to create more resilient, sustainable cities.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The Los Angeles Soft-Story Ordinance was enacted with the goal of reducing the collapse risk of woodframe buildings with soft, weak and open-front (SWOF) wall lines. Four alternative retrofit methods are permitted under the Ordinance including a “SWOF-wall-line-only” retrofit in accordance with the Department of Building and Safety requirements or a “full-story” retrofit based on Appendix A4 of the 2012 IEBC, ASCE 41-13 or FEMA P807. A comparative assessment of the increase in collapse safety provided by the four alternative retrofit methods is presented. Nonlinear static and dynamic collapse analyses are conducted on a set of archetypical structural models, which have been developed based on an extensive survey of Los Angeles SWOF buildings. The effect of several building characteristics (e.g. number of stories, wall layout in 1st story) on the relative enhancement in collapse safety of the retrofitted buildings is also investigated. The number of stories is shown to have the greatest effect on the relative collapse safety benefits derived from the alternative methods. The number of SWOF wall lines and the ductility of the upper stories also impacted the extent to which the retrofits enhanced collapse safety.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Traditional connections in earthquake-resistant cross-laminated timber buildings are susceptible of brittle failures, even when buildings are designed and supposed to be ductile. This is mainly due to the large underestimation of the actual strength of the ductile components, with consequent increased strength demand for the brittle parts, which may fail if designed with insufficient overstrength. Recent studies demonstrate that the use of steel connections characterized by a well-defined mechanical behaviour can improve significantly ductility and dissipative capacity of cross-laminated timber structures and the reliability of the capacity design. In this paper, the conceptual model of capacity design is discussed, proposing some modifications to improve its reliability for traditional and high-ductility connections for CLT structures. Results from quasi-static cyclic-loading tests of an innovative ductile bracket are presented and the corresponding overstrength factors are computed using the proposed conceptual method and compared with values available in the literature for traditional connections. Finally, a comparative application of the capacity criteria to the design of the innovative bracket and of a traditional nailed connection is presented and discussed.〈/p〉

Beschreibung: 〈p〉Unfortunately, Eqs. 2, 4 and 5 of the associated paper are published incorrectly.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The starting point of the proposed procedure for seismic evaluation of existing structures is that the yield displacement of a structure in flexure is constant and that it depends only on the yield strain of the yielding material and the geometrical characteristics of the structure, not on the yield strength of that structure. The fundamental vibration period of the structure is, thus the dependent variable derived from the estimated yield strength and yield displacement of the structure. To facilitate an evaluation of the maximum inelastic deformation of an existing structure using a corresponding single-degree-of-freedom system approach, a new relation between the yield strength (defined using a new yield strength reduction factor) and the displacement ductility demand of a corresponding single-degree-of-freedom system is proposed. This relation is consistent with the constant yield displacement assumption and characterizes the relevant properties of the structure using the yield strain of its yield material, its aspect ratio and its size. The proposed Constant-Yield-Displacement-Evaluation (CYDE) procedure for seismic evaluation of existing structures has four steps. Given an existing structure, its seismic hazard environment, and an estimate of its strength, the CYDE procedure estimates the displacement ductility demand, i.e. the maximum inelastic displacement, the structure may experience at the examined seismic hazard levels. The proposed CYDE evaluation procedure is similar to the current constant-period procedures, but provides a more realistic estimate of the displacement ductility demand for stiff structures, enabling a more accurate seismic assessment of numerous existing structures.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper describes a shake table test on a one-storey full-scale unreinforced masonry structure, which complements an earlier testing of a two-storey structure with similar characteristics. The building specimen was meant to represent the upper floors of the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. In these specimens, the masonry walls were composed of two leaves: a load-bearing inner one made of calcium silicate bricks sustaining a reinforced concrete floor and an external leaf made of clay-bricks connected to the inner leaf by means of metallic ties. A pitched timber roof was supported by two triangular gable walls. Floor acceleration response histories of the previously tested two-storey specimen were used as input motions. An incremental dynamic test, with vertical and horizontal inputs, was carried out up to the explicit collapse of some bearing elements of the structure. In particular, a two-way bending out-of-plane collapse of a load-bearing wall was observed and described.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Buckling-restrained braces (BRBs) could be installed in pares in high-rise frames or long-span structures, forming inverted-V patterned BRB systems, and the pre-compression effects are inevitably introduced into the BRB systems due to the vertical loads transmitted from upper structures. This paper presents the investigations on hysteretic performances of the inverted-V patterned BRB systems subjected to lateral cyclic loadings and vertical pre-compression. First, a parametric study via finite element (FE) analyses is conducted, considering the parameters including: pre-compression factors, vertical translational rigidity ratios, angles of the BRB systems and material properties of the BRB cores. According to the FE results, design recommendations are provided for practical designs of the BRB system and each individual BRB member. Then, based on the evaluation of the vertical and horizontal loading effects applied to the roof of a long-span structure equipped with the BRB system, formulas are proposed for designing of the long-span roof subjected to pre-compression as well as lateral earthquake effects. Finally, design procedures for the BRB system and the long-span roof are provided, which are further demonstrated by a practical design example.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Bearings acts as fusing components in bridges and transfer loads from superstructures to substructures. During earthquakes, bridge bearings may be subjected to large axial compressive loads and lateral displacements, and consequently experience severe damages. In this paper, an input energy-based (IEB) and a sliding displacement-based (SDB) damage index are proposed for quantifying seismic damage of the bridge bearings. The IEB damage index, previously proposed by authors, as the ratio of the dissipated energy to the earthquake input energy, and the SDB damage index is defined considering yielding displacement of the bearings corresponding to their sliding threshold. To evaluate the ability of the proposed damage indices in damage assessment of the bridge bearings, the force–displacement behavior of three commonly used bearings including elastomeric bearing, lead–rubber bearing, and flat sliding bearing are developed using rheological models. A set of the bearing specimens experimentally tested under cyclic/seismic loadings is adopted to calibrate the reliability of the damage indices. The results show that the IEB damage index provides a reasonably gradual progression of damage throughout the loading history and gives acceptable values for sliding and failure damage levels of the bearings more convincingly than the SDB damage model with respect to the experiment observations.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The basic goal of earthquake resistant building design codes is to provide life safety in the event of extreme earthquake loading and to reduce the seismic risk in the long run. In the most building codes including Iranian building code (Standard No. 2800), design basis earthquake is defined as an earthquake with 10% probability of exceedance (PE) in 50 years. Such an approach leads to buildings with unknown reliability, meaning that the probability of exceedance from the specified limit states in the service lifetime is not known. Furthermore, the regions with the same mapped peak ground acceleration (PGA〈sub〉DBE〈/sub〉) and different hazard curves, may have different seismic risks. Therefore, life safety is not uniformly provided across the entire region. Here, an attempt is made to estimate PGA〈sub〉DBE〈/sub〉s based on the uniform collapse risk approach for Tehran megacity. The building capacity and PGA hazard curve for 354 grids in Tehran are computed. Then, the risk-adjusted design PGA at different grid points are calculated by optimizing risk integral using the acceptance criteria of 1% in 50 years for ordinary usage buildings (risk category II). The computed risk-adjusted design PGAs vary from 0.33 g in the east to about 0.45 g toward west, south, and north. Meanwhile, the proposed mapped PGA〈sub〉DBE〈/sub〉 in standard 2800 is a constant value of 0.35 g for the whole region. To preserve a uniform collapse risk, risk-adjustment factors to modify the mapped PGA〈sub〉DBE〈/sub〉 are introduced. Furthermore, the maximum considered earthquake (MCE) required to evaluate the acceptance criteria is found to be in the range of 1.5% to 2.5% PE in 50 years. The PGAs with 2% PE in 50 years provide nearly uniform acceptable probability of collapse for buildings classified in risk category II. In addition, it is found that the buildings’ seismic importance factor (〈em〉I〈/em〉) also needs to be revised from 1.2 to 1.3 for seismic risk category III, and from 1.4 to 1.6 for seismic risk category IV to preserve the 0.5% and 0.25% collapse risk in 50 years, respectively. The outcomes also revealed that the sensitivity analysis with regard to the uncertainty of buildings’ collapse fragility curve can be ignored for buildings in risk categories I and II, while it needs to be performed for buildings in risk categories III, and especially IV. Finally, the estimated PGA hazard curves of the Tehran megacity are approximated by the cubic functions to expedite the future risk assessment studies in Tehran megacity.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Reinforced Autoclaved Aerated Concrete (AAC) wall panels are more commonly used to construct load-bearing walls in low-rise prefabricated buildings located in seismic zones. In the scope of this study, the seismic response of buildings constructed with reinforced AAC wall panels was investigated. To this end, an in situ test was conducted on a two-story test building under reversed cyclic displacement excursions. It was determined that the test building could carry a lateral load of 60% more than its weight and has a global displacement ductility of about 3.5. The first story of the building was observed to be critical and the failure of the building was due to overturning response of the whole system. In addition, the proposed numerical models for simulating the behavior of the AAC wall panels were validated. These calibrated numerical models were utilized to conduct nonlinear static analysis of the test building and a reasonably good agreement was observed between the test results and simulations. The results of the incremental dynamic analyses demonstrated that i) the two-story test building could resist strong ground motions with PGA values up to 0.6 g without undergoing significant plastic deformations and ii) a reserve of ductility and over strength is available for the AAC panel building to survive earthquakes with PGAs reaching nearly 0.6 g. Based on these numerical results, reinforced AAC wall panel buildings appear to be good alternatives for low-rise construction in seismic regions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A seismic performance assessment of historical Kütahya Kurşunlu Mosque in Turkey is presented before and after it has been retrofitted. Site investigations were carried out to identify structural conditions, in which severe cracks, especially on the dome, were mapped. Regarding damage conditions, the Mosque has undergone several interventions, including retrofitting actions, in order to improve its seismic performance and global structural behavior. Effectiveness of seismic retrofitting of the Mosque was investigated by using the finite element method. Two representative structural models of the Mosque, namely non-retrofitted and retrofitted, were generated as a three-dimensional finite element model using an advanced structural analysis software. Ambient vibration measurements were performed to identify modal properties of the Mosque. Thus, the finite element model was calibrated and improved according to the experimental modal data. Nonlinear pushover and dynamic analyses were conducted to evaluate the seismic performance of the historical Mosque. This paper aims to demonstrate the effectiveness of the adopted retrofitting by comparing the models (before and after retrofitting) and, also, to validate the nonlinear behavior of the model by comparing it with the existing damage on the Mosque.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper presents results from an experimental program aimed at investigating the in-plane seismic behavior of thick perforated walls from existing earthen constructions. Two full-scale earthen wall specimens with dimensions of 7.0 × 3.45 × 0.6 m and door and window openings were subjected to cyclic lateral loads. Walls were made of adobe bricks and rammed earth (RE). The specimens were found to sustain a maximum drift of 0.46% only with distinctively different damage patterns that consist of few large cracks for the RE wall and a wide spread of cracking for the adobe wall. The RE wall had higher lateral load capacity and higher energy dissipation as compared to the adobe wall. Implementation of a simple retrofitting scheme consisting of vertical and horizontal timber straps along with post-tensioned rods proved to be very efficient after re-testing the damaged walls. Not only the initial lateral stiffness of each specimen was restored, but also the lateral load capacity increased by as much as 70% in both specimens. Most notably, the retrofitted walls had lateral deformation capacity five times bigger (2.5% drift) and dissipated almost 10 times the amount of hysteretic energy compared to the original specimens. It was also found that a concrete damage plasticity model could be successfully calibrated to estimate the cyclic response of both original and retrofitted RE walls with a reasonable degree of accuracy, and thus highlighting the possibility for more generalized numerical models to investigate other earthen wall geometries and retrofitting alternatives.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In this paper, unreinforced masonry (URM) and retrofitted masonry walls are modeled experimentally and computationally. The walls were subjected to in-plane loading to assess on the effectiveness of a retrofit solution that makes use of near surface mounted (NSM) reinforcing steel bars. A laboratory testing campaign was performed that included pull-out tests, diagonal compression tests, and in-plane cyclic tests of URM and NSM retrofitted physical models. The experimental results indicate that the NSM reinforcing steel bars are effective in improving the deformation capacity of the URM walls. A computational modeling approach that makes use of the applied element method is proposed and the computational results are validated using the experimental tests presented. Results from computational models indicate that a good correlation with the test results is achieved in terms of load-displacement response as well as failure mechanisms observed.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In this study, the results of experimental tests performed on unreinforced masonry infill walls are presented. The out-of-plane response of infills different for the thickness and for the boundary conditions but equal for the construction procedure and the materials used is investigated. Infills with two different height-to-thickness slenderness ratios are tested. In addition, three different boundary conditions at edges are considered. The experimental results are used to assess, for different values of the slenderness ratio, the effectiveness of the out-of-plane strength formulations for unreinforced masonry enclosures in which the mono-directional or bi-directional arching mechanism can occur. A discussion on the different post-peak response of specimens with different boundary condition (brittle, for vertical spanning infills, non-brittle for infills mortared along three or four edges to the confining elements) is also presented. In the case of one-way arching, literature and code models underestimate the out-of-plane strength of thinner specimens and overestimate it for thicker specimens. In the case of two-way arching, all the existing strength formulations are significantly conservative and potentially adequate for a code-based safety check of unreinforced masonry infill walls under out-of-plane seismic demand.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper discusses the development of a publicly available database of composite steel beam-to-column connections under cyclic loading. The database is utilized to develop recommendations for the seismic design and nonlinear performance assessment of steel and composite-steel moment-resisting frames (MRFs). In particular, the sagging/hogging plastic flexural resistance as well as the effective slab width are assessed through a comparison of the European, American and Japanese design provisions. The database is also used to quantify the plastic rotation capacity of composite steel beams under sagging/hogging bending. It is found that the Eurocode 8-Part 3 provisions overestimate the plastic rotation capacities of composite beams by 50% regardless of their web slenderness ratio. Empirical relationships are developed to predict the plastic rotation capacity of composite steel beams as a function of their geometric and material properties. These relationships can facilitate the seismic performance assessment of new and existing steel and composite-steel MRFs through nonlinear static analysis. The collected data underscores that the beam-to-column web panel zone in composite steel beam-to-column connections experience higher shear demands than their non-composite counterparts. A relative panel zone-to-beam resistance ratio is proposed that allows for controlled panel zone inelastic deformation of up to 10 times the panel zone’s shear yield distortion angle. Notably, when this criterion was imposed, there was no fracture in all the examined beam-to-column connections.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉An important consideration for the adoption of stochastic ground motion models in performance-based earthquake engineering applications is that the probability distribution of target intensity measures from the developed suites of time-histories is compatible with the prescribed hazard at the site and structure of interest. The authors have recently developed a computationally efficient framework to modify existing stochastic ground motion models to facilitate such a compatibility. This paper extends this effort through a validation study by comparing the seismic demand of recorded ground motions to the demand of stochastic ground motion models established through the proposed modification. Suites of recorded and stochastic ground motions, whose spectral acceleration statistics match the mean and variance of target spectra within a period range of interest, are utilized as input to perform response history analysis of inelastic single-degree-of-freedom (SDoF) case-study systems. SDoF systems with peak-oriented hysteretic behavior, strain hardening, and (potentially) degrading characteristics, experiencing different degree of inelastic response, are considered. Response is evaluated using the peak inelastic displacement and the hysteretic energy given by the work of the SDoF restoring force as engineering demand parameters (EDPs). The resultant EDP distributions are compared to assess the effect of (and validate) the proposed modification. It is shown that the proposed modification of stochastic ground motion models can provide results that are similar to these from recorded ground motion suites, improving any (in some cases large) discrepancies that exist for the initial, unmodified stochastic ground motion model.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Due to the brittle nature of wood material, the dissipation of seismic energy in timber structures is typically ensured through yielding of the mechanical connectors, where plastic deformations are developed in fasteners that have adequate ductility and cycle-fatigue strength. These structural components are denoted dissipative zones, whereas all other structural elements are assumed to behave elastically. Such elements are designated as non-dissipative zones and are designed with sufficient over-strength, to meet the requirements of capacity-based design (CD). Despite the general consensus that using the principle of CD could lead to safe buildings, where brittle failures are avoided, the applicability of such approach to light frame timber (LFT) and cross laminated timber (CLT) buildings has lacked analytical expressions that depend on the structural typology and failure mechanism. The current paper aims to fill this gap in knowledge by proposing an analytical approach that incorporates the CD philosophy to LFT and CLT buildings at the substructure (wall) and super-structure (building) levels. A simplified approach is adopted for structures with a low-to-medium energy dissipation capacity whereas a more rigorous approach is presented for structure with a high energy dissipation capacity. An experimental comparison and design example is included to present the applicability of the proposal.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A new stochastic ground motion prediction equation (GMPE) for low and diverse seismicity region, i.e., Peninsular India has been derived for a wide range of magnitude (〈span〉 〈span〉\(M_{w}\)〈/span〉 〈/span〉 4–8) and distance (10–500 km). Source, path, and site terms have been determined by comparing the recorded and simulated response spectra using derived values from the literature. Uncertainty has been assessed through simulation by random sampling of the corresponding distribution of all the input parameters. To capture the non-uniform seismicity of Peninsular India, GMPE has been derived using constant stress and variable stress model. The synthetic data has been regressed using linear mixed-effect model algorithm by determining the functional form that is compatible for magnitude and distance scaling. Sensitivity analysis has been used in determining the impact of uncertainty of each input parameter on GMPE standard deviation. Further, new GMPEs have been validated using the recorded ground-motion data.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Due to the stable hysteretic behavior, buckling-restrained braces (BRB) have been increasingly adopted in reinforced concrete (RC) frame structures to develop a dual structural system. This investigation aims to quantify the seismic behavior of newly-constructed reinforced concrete BRB frames (RC-BRBFs). The force–deformation characteristic of dual RC-BRBFs is firstly presented and the yield displacement is derived using the story shear ratio resisted by BRB system. The seismic design procedure of dual systems for different BRB configurations (including single diagonal, V-type and inverted V-type), is developed using the performance-based plastic design approach by considering BRB postyield behavior, design target drift and global yield mechanism. 126 RC-BRBF structures corresponding to different story numbers, BRB configurations and story shear ratios are designed. The influence of story shear ratios on the design results is analyzed. The seismic response of structures subjected to 22 ground motions is investigated and compared in terms of yield mode, maximum interstory drift ratio, BRB maximum ductility and cumulative ductility, and residual drift ratio. The relationship between actual and design normalized story shear of BRBs is demonstrated and a fitting equation is proposed to quantify the actual story shear ratios. The analytical results of the present study can provide quantified insights to the seismic design of RC-BRBF structures.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Presence of infills in reinforced concrete (RC) frames enhances the lateral load behavior of the bare frame system, but makes the columns vulnerable to shear failure under strong ground motions. This local adverse effect of infill is more pronounced in exterior ground storey columns where strong and stiff infills are present on one-side of the columns. Some of the current seismic standards address the local adverse effect of infill using variety of recommendations but their application is limited. Therefore, it is of primary importance to develop methods to counteract the adverse effect of infill. To prevent or delay the shear failure of columns, three methods (increasing the dimensions of the columns taking care of the effect of infill, using weak and soft masonry to reduce the effect of infill on columns, and decreasing the frame-interaction using collector beams in infills) were adopted in the present experimental study. From the results, it was observed that the methods not only enhanced the lateral load behavior, but also delayed the shear failure of columns without compromising the other functional requirements. The three methods can be efficiently used in both existing and new constructions to reduce the seismic vulnerability of masonry infilled RC frame buildings.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The increased aesthetic appeal of columns with flares resulted in bridge configurations with flared columns during the 1970–1990 design periods in California. Earthquake reconnaissance reports indicated that the flare is detrimental on the structural functionality of the bridge with some geometric configurations. This research examines the relative vulnerability of bridge configurations with flared and non-flared columns for three-span two-column bent bridges with oblong cross-sections. The numerical model of the columns with and without flare is calibrated with existing experimental results. The calibrated models are used to develop the fragility curves for California bridges. Fragility curves for each bridge class are generated by accounting for the material, geometric, and structural uncertainties, and the effects of column flare on the seismic demand and fragility of bridges are investigated in detail in this paper. Results reveal that the presence of column flare for the case study bridges increases the stiffness and strength of columns because of a low potential of column shear failure, resulting in the reduction of bridge vulnerability and have beneficial effects on the structural functionality. Thus, the flare does not necessarily reduce the seismic performance for all bridge cases and depends on the failure mode associated with the bridge configuration. The fragility curves suggested in this research can be used by stakeholders in deciding the retrofitting and maintenance strategies of bridges with architectural flares.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Intermediate isolation system (IIS) is currently spreading and gaining significant popularity, mainly in Japan. However, its potentials are not so well-known in European countries, and in USA only one application to building retrofit is registered. The dynamic behaviour of intermediate isolation systems, more complex than the two-degree-of-freedom behaviour of base isolation systems, gives rise to a twofold control mode, which combines isolation and mass damping strategies. However, the research contributions provided in the scientific literature usually concentrate on one single control mode, either isolation or mass damping, and the relevant design methods and criteria. This paper addresses the IIS design problem from a wider perspective and presents an explorative study on the vibration characteristics and dynamic behaviour of IIS, in order to identify the range of different behavioural modes and to propose relevant design guidelines. For these aims, a parametric analysis is carried out, varying the main design parameters, namely: isolation period and ratio, location of isolation layer and mass ratio, distributions of stiffness and mass in the upper and lower structures. A classical modal approach is initially assumed for assessing the contributions of each vibration mode on the global dynamic behaviour of IIS, with a particular focus on the effect of coupling of higher modes. However, since IIS is a non-proportionally damped system, a state space formulation is subsequently adopted for establishing the cases for which the simplified classical approach, only considering two damping values for the isolation and structural parts, can be adopted in a preliminary design stage. Finally, frequency response analysis is carried out for identifying the ranges of predominant isolation and mass damping behaviour and the effect of mode coupling both in terms of local and global response of the isolated models. Design implications are finally derived from the analysis results.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This study aims to increase the knowledge of the seismic behaviour of low-to-medium rise structures, in which the seismic force-resisting system is provided by cold-formed steel strap-braced walls designed as non-energy-dissipating systems. The dynamic response of this system under seismic actions is analysed by performing shake table tests on two reduced-scale (1:3) three-storey two-bay prototypes, that differed in floor typology: steel–concrete floors (Type 1) or floors made of wood-based panels (Type 2). Main outcomes show that the seismic response can be considered as satisfactory, because the system seems to have inherent ductility even without a designated energy dissipating mechanism. In particular, the seismic response was approximately linear for tests having intensity not greater than that assumed for the design, whereas for tests having higher intensities the behaviour deviated from the linearity, with maximum interstorey drift angles greater than 2% without very extensive damage, and in-plane floor rigid behaviour for both prototypes according to the ASCE 7 definition.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This study investigates the suitability of various intensity measures for conducting probabilistic seismic risk assessment of low- to mid-rise non-ductile reinforced concrete buildings with various plan configurations located in low-to-moderate seismic regions. Probabilistic seismic demand models are developed by conducting three-dimensional nonlinear time history analyses. The building response is defined to be dependent on component response and interstorey drift limits. In total the suitability of eleven intensity measures is evaluated by examining five criteria: efficiency, practicality, proficiency, sufficiency, and hazard computability. Based on the first four criteria it is identified that peak ground velocity, peak ground displacement, and maximum spectral displacement response are the most suitable intensity measures. Hazard computability is then utilised to select the optimum intensity measure for a hazard model in accordance with the Australian standards.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In this paper, a new yielding dissipater device is introduced for seismic protection of concentrically braced structures. The device is fabricated by a set of transverse plates inserted in the middle of a diagonal brace. The special configuration of the new device transforms the axial force of a concentric brace to pure bending in the dissipater plates. The dissipater plates are designed to bend inelastically over their whole surface to dissipate energy. Welding is avoided in the dissipater plates and consequently the ductile behavior of steel results in a good hysteric behavior of the new device. Experimental results of sixteen specimens of the proposed dissipater device show a stable hysteretic behavior of the brace and similar behavior in tension and compression. An analytical model is developed and verified to predict the behavior of the proposed dissipater.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Iran is located in one of the most seismically active regions of the world. This high seismicity combined with densely populated regions has led to several destructive earthquakes in the past, such as the M7.4 Tabas (1978), M7.4 Manjil–Rudbar (1990), or the M6.6 Bam (2003). Seismic hazard and risk assessment can provide critical information to decision makers for the development of efficient risk reduction measures. In this study, exposure models for the residential, commercial and industrial building stock were developed using recent housing census information, socio-economic data and the judgement of local experts. For each building class in the exposure model, a set of fragility and vulnerability models was derived using nonlinear time history analysis and ground motion records from the region. The exposure and vulnerability models were combined with the recently released Earthquake Model for the Middle East (EMME) to estimate probabilistic earthquake losses using the OpenQuake-engine. These results identify the regions within the country with the highest risk, the most vulnerable building classes, and the expected economic losses for a number of return periods.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Probabilistic seismic hazard analysis (PSHA) is generally recognized as the rational method to quantify the seismic threat. Classical formulation of PSHA goes back to the second half of the twentieth century, but its implementation can still be demanding for engineers dealing with practical applications. Moreover, in the last years, a number of developments of PSHA have been introduced; e.g., vector-valued and advanced ground motion intensity measure (IM) hazard, the inclusion of the effect of aftershocks in single-site hazard assessment, and multi-site analysis requiring the characterization of random fields of cross-correlated IMs. Although software to carry out PSHA has been available since quite some time, generally, it does not feature a user-friendly interface and does not embed most of the recent methodologies relevant from the earthquake engineering perspective. These are the main motivations behind the development of the practice-oriented software presented herein, namely REgionAl, Single-SitE and Scenario-based Seismic hazard analysis (REASSESS V2.0). In the paper, the seismic hazard assessments REASSESS enables are discussed, along with the implemented algorithms and the models/databases embedded in this version of the software. Illustrative applications exploit the potential of the tool, which is available at 〈a href="http://wpage.unina.it/iuniervo/doc_en/REASSESS.htm"〉http://wpage.unina.it/iuniervo/doc_en/REASSESS.htm〈/a〉.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Columns of masonry infilled reinforced concrete frames are prone to shear failure due to the detrimental effect of infill under lateral earthquake loads. This effect is catastrophic in ground storey columns, where the shear force demand is very high. The primary objective of the study is to understand the applicability of the codal recommendations to estimate the shear demand on the columns realistically, and propose an alternative solution for prediction of shear failure of columns by improving the existing macro-modelling techniques. Half-scaled specimens of masonry infilled RC frames tested in an experimental study were considered to evaluate the proposed improvements. Applicability of the improved macromodel was also verified with the results obtained in other past experimental studies. The proposed simplified analytical modelling technique can be used for practical engineering purposes to assess the shear failure of columns and can be utilized for designing or strengthening the shear deficient columns in such frames.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A multiple level-of-detail (LOD) simulation framework is proposed in this study, to take full consideration of the diversity of structural types, available data, and simulation scenarios in an actual application of seismic-damage simulation to urban buildings. Firstly, key features of the frequently used seismic simulation methods for buildings are discussed, and logical relationships of these simulation methods, as well as the available multi-source data, are established in different LODs. Secondly, implementation of the proposed multi-LOD simulation framework is presented, and a unified city data structure is proposed to enable effective management and storage of data with different LODs. Finally, the Beijing central business district, which has various types of buildings, is investigated in detail to demonstrate the proposed multi-LOD framework. The accuracy, efficiency, and corresponding requirements of different LOD simulations are compared and discussed. The outcomes of this work are expected to provide a useful reference for the application of seismic-damage simulations in complex urban areas.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The economic benefits of utilizing numerical simulations versus experimental approaches in geotechnical studies have made them viable tools for engineering assessments. Within this framework, the damages due to earthquake-induced forces and displacements in liquefied ground are amongst the phenomena investigated by many researchers. In the current study, numerical simulation of mildly-sloping liquefied ground under dynamic loading is conducted by the graphical user interface OpenSeesPL, which uses the open-source computational platform OpenSees. Pile-pinning lateral displacement mitigation method in saturated sand is modeled and the effects of artificial earthquake time histories covering a range of different durations and frequency contents on the system response are scrutinized. It is observed that duration and frequency content of the earthquakes changed the initiation time of large deformations. Higher pore pressures were generated in low frequency systems and larger lateral displacements of the improved ground with loose soil were countered with lower accelerations due to the liquefied ground isolating effects. The reliability of different intensity measures for enabling seismic performance assessments are discussed and finally, recommendations for practical hazard evaluations are made.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Seismic assessment of existing buildings is usually treated by international codes and guidelines through a semi-probabilistic approach based on the use of the so-called confidence factor (CF). Many authors revealed the inadequacy of such an approach, proposing alternative procedures based on: the updated calibration of the CF values together with its application to a parameter better representative of the structural response than the material strength, as usually adopted by codes; or the fully probabilistic approach by explicitly considering the propagation of uncertainties. Although the latter constitutes the most rigorous approach, it is still computationally demanding and difficult to be integrated as standard tool in the engineering practice. In this paper, the model parameter sensitivity analysis is proposed to support the seismic assessment in various aspects such as: pointing out, in an explicit way, the influence each uncertain parameter has on the structural response; supporting the set of an effective investigation plan; computing the essential parameters for a probabilistic-based verification on basis of a limited number of analyses. To the latter aim, the results from the model parameter sensitivity analysis executed according to the star design with central point approach are used to determine the median intensity measure (〈em〉IM〈/em〉〈sub〉〈em〉LS〈/em〉〈/sub〉) and, with the help of the surface response technique, its dispersion (〈em〉β〈/em〉〈sub〉〈em〉LS〈/em〉〈/sub〉), that are the two parameters of the fragility curve representing the capacity in the assessment. The proposed methodology is applied on two case studies, representative of existing URM buildings. Firstly, the〈em〉 IM〈/em〉〈sub〉〈em〉LS〈/em〉〈/sub〉 and〈em〉 β〈/em〉〈sub〉〈em〉LS〈/em〉〈/sub〉 values are calculated and thus compared, for the aim of validation, with the reference ones obtained from nonlinear static analyses performed on a large number of models generated using Monte Carlo simulations. Results obtained show a good estimate of the fragility curve parameters, compared to the rigorous probabilistic approach, highlighting the potential of the procedure proposed.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The vulnerability of bridges depends primarily on the seismic performance of its piers. This paper studies the seismic vulnerability of a bridge with conventional concrete and hybrid fibre reinforced concrete (HyFRC) pier. Combination of 1.0% steel fibres and 0.15% polypropylene fibres by volume fraction is adopted in the construction of HyFRC piers from the viewpoint of improved toughness. Hybrid testing of six bridge piers (three made of conventional concrete and three made of HyFRC) are carried out to obtain the limit-state capacities and numerical model of the bridge structure is calibrated using the experimentally obtained responses. Analytical fragility curves are developed using the calibrated numerical model for different damage states as a function of an engineering demand parameter that represents the ground motion. The damage states are decided based on the actual damages observed from the experimental investigation. The fragility curves show very clearly that at any damage state, the HyFRC piers are less vulnerable to earthquakes when compared to the bridge piers made of conventional concrete. The difference in probability of exceedance increases with an increase in the intensity of earthquake. Use of HyFRC in bridge piers can provide significant enhancement in seismic performance of bridges in earthquake-prone regions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In seismic assessment of bridges the research focus has recently shifted on the derivation of bridge-specific fragility curves that account for the effect of different geometry, structural system, component and soil properties, on the seismic behaviour. In this context, a new, component-based methodology for the derivation of bridge-specific fragility curves has been recently proposed by the authors, with a view to overcoming the inherent difficulties in assessing all bridges of a road network and the drawbacks of existing methodologies, which use the same group of fragility curves for bridges within the same typological class. The main objective of this paper is to critically assess the necessity of bridge-specific fragility analysis, starting from the effect of structure-specific parameters on component capacity (limit state thresholds), seismic demand, and fragility curves. The aforementioned methodology is used to derive fragility curves for all bridges within an actual road network, with a view to investigating the consistency of adopting generic fragility curves for bridges that fall within the same class and quantifying the degree of over- or under-estimation of the probability of damage when generic bridge classes are considered. Moreover, fragility curves for all representative bridges of the analysed concrete bridge classes are presented to illustrate the differentiation in bridge fragility for varying structural systems, bridge geometry, total bridge length and maximum pier height. Based on the above, the relevance of bridge-specific fragility analysis is assessed, and pertinent conclusions are drawn.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Fragility functions are an important tool in earthquake engineering, used to compute the probabilities of different damage states as a function of seismic response. They can be developed for large systems like buildings and bridges, as well as for individual structural and non-structural components, such as those used in the FEMA P-58 Seismic Performance Assessment Procedure. There are currently a number of problems associated with some P-58 non-structural mechanical component fragility functions and related loss predictions, including non-convergence when fitting the fragility functions in some cases and non-monotonic loss predictions. In this study, we recommend improvements to these fragility functions and loss predictions. Firstly, we recommend using the maximum likelihood method to fit the fragility functions to the underlying empirical data. This mitigates the non-convergence problems when fitting and makes predictions that better align with damage observed in past events. To compute predicted losses for anchored mechanical components, it is necessary to additionally consider anchorage damage, which can be predicted using fragility functions based on building code provisions. We recommend refining the current FEMA P-58 method for predicting anchored mechanical component losses, such that component and anchorage damage are calculated directly according to their corresponding fragility functions. The proposed method yields more intuitive loss predictions that vary monotonically with anchorage capacity. It also leads to better predictions of losses relative to damage observed in previous events. If implemented, the recommendations made in this paper would enhance the FEMA P-58 Seismic Performance Assessment Procedure.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Buildings with the singly symmetric plan are more vulnerable to earthquake actions than the buildings with a symmetric-plan arrangement since the torsional effect caused by the asymmetricity will induce higher seismic demand and may cause unexpected damage to the buildings. Thus, it is a crucial challenge for researchers and engineers to predict seismic demands of asymmetric-plan buildings for the possible strengthening and retrofitting. Although some pushover-based analysis methods have been proposed for the fast prediction of asymmetric-plan buildings, most of them do not reasonably consider the dynamic coupling of vibration modes. This paper expands the spectrum-based pushover analysis (SPA) procedure, which is proved to be effective in predicting seismic demands of buildings with symmetric building plans, to three-dimensional structure systems, to estimate the seismic demands of singly symmetric structures. A comprehensive case study, which includes six frame buildings with different structural heights and mass eccentricity ratios under various levels of the input motions, was conducted to investigate the feasibility of the SPA method in estimating the seismic demands of one-way asymmetric-plan buildings. It is found from the comparison of seismic demands computed from the SPA method, the nonlinear response time history analysis, the consecutive modal pushover analysis and the modal pushover analysis that the SPA method is capable of predicting the seismic demands very well, in particular, the demands on the heavy side of the structure, where the seismic demand and damage are more significant.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Reinforced concrete frame with masonry infill (RCFMI) buildings comprise a significant proportion of commercial buildings constructed prior to the adoption of New Zealand’s modern seismic design codes in 1976. The characteristics and seismic performance of RCFMI buildings have not been previously investigated at a national level. As part of the study reported herein, efforts were made to identify and document building characteristics, including building address, infill type (clay-brick or concrete-block masonry infill), wall morphology (cavity or solid wall), geometry (building footprint and height), building continuity, and age of construction. During sidewalk surveys the characteristics of 203 and 55 RCFMI buildings were observed and well documented in the Auckland and Dunedin regions, respectively. The surveyed RCFMI buildings were assigned to one of four typologies according to infill type and wall morphology. In addition to cataloguing the national stock of RCFMI buildings and investigating their characteristics, the study outlined herein was designed to provide a forecast of the earthquake vulnerability of existing commercial RCFMI buildings in New Zealand in an effort to quantify the cumulative earthquake risk.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In the Kribi region (south-western Cameroon), a new industrial harbour has been built. This area is marked as a low-seismicity zone, according to the global seismic hazard map. This estimate is based, however, on a poorly documented data set. Industrial harbours are critical facilities and, consequently, appropriate cautions have to be taken in the seismic design. This paper illustrates the methodology adopted to compute the expected ground motion for the seismic design of the new harbour, starting from the available information. The standard probabilistic seismic hazard assessment is based on a logic tree approach considering areal and fault sources with two earthquake rate models (characteristic earthquake and Gutenberg–Richter), and two ground motion prediction equations. As expected, the obtained ground motion at the bedrock for a return period of 475 years is not very large [0.07 g, in terms of horizontal peak ground acceleration (PGA)] with a well marked peak between 0.1 and 0.2 s. This result is in agreement with that of the Global Seismic Hazard Assessment Project, where a general PGA between 0.04 and 0.08 g is associated with south-western Cameroon. The effects of local site conditions are evaluated through geophysical methods (single station and array surveys) and 1D linear-equivalent numerical modelling. Considering the two geotechnical models identified in the study region, by a specific geophysical survey executed during this study, local amplifications of 1.9 and 2.2 have been calculated for the two sectors, respectively. Furthermore, the results obtained, in terms of uniform hazard response spectra, have been used as guidelines to determine the design ground motions for the maritime and land infrastructures planned in the Kribi harbour area. This study represents a summary of the present knowledge on the seismicity of this part of Africa as well as the first regional and local seismic hazard assessment for the Kribi area.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The paper deals with the seismic vulnerability of masonry vaults: a review of the results of an experimental campaign recently performed by the authors and a numerical study are presented. In particular, the effectiveness of a strengthening technique based on the application, at the vault extrados or intrados, of a 30 mm thick mortar coating with glass fiber-reinforced polymer meshes embedded is discussed, referring to vaults carrying their self-weight and subjected to a lateral transversal load. The role of the connection of the vault with its abutments is particularly emphasised in this review of the experimental results, evidencing how slides and/or uplifts at the spring sections can reduce the strengthening effectiveness. The numerical study, based on non-linear static analysis, allowed to investigate in depth into the effects of an inadequate skewback configuration: it was found that a ductile connection, which allows plastic rotation at the spring section while maintaining the bending resistance and avoiding shear slip and uplift, is the optimal solution. Moreover, the results of a sensitivity study are also presented, as this permits to evaluate the incidence of the different mechanical and geometrical parameters on the behavior of the vaults and provides useful indications towards a proper design and optimization of the strengthening intervention.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper presents ground motion models to predict vertical components of peak ground acceleration, peak ground velocity, and 5%-damped response spectral acceleration at periods ranging from 0.01 to 10 s. These models are derived from the comprehensive Iranian strong ground-motion database containing 1350 three-component time-histories recorded during 370 earthquakes with 4.5 ≤ 〈span〉 〈span〉\({\text{M}}_{\text{w}}\)〈/span〉 〈/span〉 ≤ 7.4. Possible regional dependency of vertical ground-motions to characteristics of three seismo-tectonic regions in Iran was investigated through analysis of variance (ANOVA) technique. Consistent models based on four distance measures; two for point-source (〈span〉 〈span〉\({\text{R}}_{\text{epi}}\)〈/span〉 〈/span〉 and 〈span〉 〈span〉\({\text{R}}_{\text{hyp}}\)〈/span〉 〈/span〉) and two for finite-fault (〈span〉 〈span〉\({\text{R}}_{\text{JB}}\)〈/span〉 〈/span〉 and 〈span〉 〈span〉\({\text{R}}_{\text{rup}}\)〈/span〉 〈/span〉), were developed. The distribution of inter and intra-event residuals presents satisfactory agreement between actual data and our proposed vertical ground motion prediction equation (GMPE). Furthermore, a detailed comparison between our predictions and four local and global GMPEs is presented, well as horizontal model of Darzi et al. (Bull Seismol Soc Am. 〈span〉https://doi.org/10.1785/0120180196〈/span〉, 〈span〉2018〈/span〉). In addition, this study provides period-dependent correlation coefficients between epsilons of different GMPEs corresponds to either horizontal, vertical, or vertical-to-horizontal spectral ratio intensity measures as a function of single or two-periods of interest.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Two different approaches are considered by seismic codes for estimating the seismic drifts of moment resisting steel frames (MRSFs). The first approach which is adopted by the European and the Canadian codes is driven by the equal displacement rule and defines the deflection amplification factor (DAF) to be equal to the response modification factor R. The second approach which is motivated by the opinion of professionals who believe that the equal displacement rule often over-estimates displacements is employed by the ASCE 7-10 and the Egyptian seismic code, where the DAF is considered equal to a fraction of R. This study evaluates the two approaches considered for estimating the seismic drifts of MRSFs. Four MRSF buildings having 2-, 4-, 8- and 12-stories have been designed under variable levels of seismic intensity. Five lateral-stiffness scenarios are considered for each building to account for the stiffness increase due to the nonstructural components as well as the modeling approximations. The seismic drifts of the MRSFs are calculated under the effect of twenty-two pairs of far-field ground motion records by time history analysis and with using the code simplified approaches. The results obtained indicate that the current code approaches of amplifying the elastic drifts significantly overestimate the seismic drifts of buildings designed under low level of seismicity. In contrast, the ASCE 7-10 and the Egyptian code approaches of estimating the seismic drifts underestimate the maximum story drift ratios under earthquake loading for long period buildings designed under high level of seismicity.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The paper presents a ground motion prediction equation (GMPE) for the vertical pseudo spectral acceleration for periods varying from 0.02 to 4 s. The model is derived from the same strong motion database as previously considered for the horizontal GMPE for Algeria (Laouami et al. 〈span〉2018〈/span〉). 583 vertical records homogeneously processed having magnitude and distance intervals of 3–7.4 and 1–150 km respectively are used. The functional forms are similar to those used for our horizontal GMPEs. To consider the soil factor, three soil classes are defined based on the horizontal over vertical spectral ratios: rock, firm and soft. Estimates of period-dependent site coefficients reveal negligible vertical site amplifications compared to the horizontal ones. This work also presents a model for vertical over horizontal (V/H) response spectral ratio derived from the vertical and the horizontal GMPEs. One found, particularly for small distances and large magnitudes, that the V/H ratio has a large peak, which may exceed unity, around the period range 0.04–0.1 s. This result may be very important for seismic behavior of stiff structures which vertical fundamental period’s lies within a period range 0.04–0.15 s. The derived horizontal and vertical GMPE’s are used to compute predicted H/V spectral ratios for given scenarios. Compared to the recorded mean H/V spectral ratios, this tool allows checking the confidence level of the site classification scheme. Comparison of the median V/H response spectral ratios with period predicted from the model of this study with those from the Algerian seismic code RPA99 (〈span〉2003〈/span〉) and the EC-8 (2004) (type 1 and type 2) reveals that the definition of the V/H spectral ratio from the RPA99 is closer to the scenario (M = 7 and R〈sub〉jb〈/sub〉 = 100 km). Unfortunately, this scenario is not the worst for the vertical component. The present study has shown that the worst case scenario is related to high magnitude and short distance. For this scenario, for which the RPA99s do not provide an adequate V/H ratio, the EC-8 type 1 appears to give higher values. The proposed vertical GMPE for Algeria is compared with recent published models. It results that the present model with those from Cagnan et al. (〈span〉2016〈/span〉) and Stewart et al. (〈span〉2016〈/span〉) are the most recommended for the seismic hazard analysis in Algeria.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper presents a methodology to perform seismic fragility analysis of deteriorating reinforced concrete (RC) bridge columns induced by corrosion based on time-variant capacity estimates. The typically simplified uniform reduction model of cross-section of a corroded reinforcing steel bar is assumed, and the strain penetration and slippage of reinforcements anchored to the foundation are considered in the performance assessment of corroded bridge columns. To be conveniently used in engineering practice, the drift ratio is taken as the capacity index to quantify various damage states, and the plastic hinge model is adopted and verified to calculate the tip displacement of corroded columns due to its simple form and wide use in elastic–plastic analysis. Seismic fragility curves are then developed with reference to both the pristine (or original) construction state and current deteriorated state to illustrate the differences of potential damage probabilities calculated by time-invariant and time-variant capacity indexes. Further, significance test is performed. The results highlight that some of the empirical plastic hinge length models can also be used to predict the ultimate displacements of corroded columns by introducing the corroded constitutive models of materials; the seismic performance of a deteriorating RC bridge column will be significantly underestimated by using pristine capacity index as the measurement criterion. As a matter of fact, in engineering practice, one of the main concerned issues should be the current structural failure probability when evaluating the performance of a deteriorated RC structure. Hence, it is suggested that the time-variant capacity index should be adopted to estimate the seismic performance of a deteriorating RC structure during its life cycle.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The efficiency of strengthening of unreinforced hollow clay block masonry buildings with fibre reinforced mortar coatings has been investigated. A full scale three-storey building model and a series of accompanying walls have been built and tested. Reference unstrengthened, and strengthened specimens of each type have been tested by subjecting them to cyclic shear at constant compressive load. First, the three-storey model was tested in its original state until the maximum resistance was attained and major, but still repairable damage, developed in the walls. Then, the damaged model was strengthened with fabric reinforced cementitious mortar coating and re-tested up to near collapse limit state. Typical storey mechanism was observed in original and strengthened state, with the majority of damage concentrated in the walls of the bottom storey. Diagonally oriented shear cracks prevailed in the elements in the direction of loading. The behaviour of single walls in cyclic shear tests was similar to that observed in the piers of the building models. The analysis of test results indicated that the resistance and displacement capacity of unreinforced masonry structures of the particular type tested can be significantly improved if delamination and separation of coating is prevented. Finally, a calculation model for the assessment of seismic resistance of reference and strengthened building model is presented and the comparison between calculated and experimental results discussed.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The friction pendulum bearings (FPB) begin to be used in railway bridges in China. In one earthquake region in China, the shear pins of FPB are required to be well to provide the enough shear force and stiffness under service loads (such as the vehicle forces being less than 170 kN in the longitudinal direction and 40 kN in the transverse direction) or small earthquake loads with a peak ground acceleration (PGA) being less than 0.1 g, however, are cut off to isolate seismic energy under large earthquake loads with a PGA being larger than 0.2 g. It is necessary to identify the appropriate strength of FPB shear pin to satisfy the above requirements. This paper selected the simply supported bridges on a single-line railway in the above earthquake region as the study object, which had a span length of 32 m and two height types of piers (8 m and 25 m). A prototype finite element model (FEM) and a scaled FEM were numerically analyzed, and a scaled experimental model was tested on shake table for each bridge. The results of them were compared with each other to validate the rationality of all models and to achieve the appropriate strength of FPB shear pin. The results show that the appropriate strengths of FPB shear pins are 540 kN in the longitudinal direction and 300 kN in the transverse direction for the bridge with the pier height of 8 m. Likewise, 350 kN and 270 kN are determined as the appropriate strengths of FPB shear pins for the bridge with the pier height of 25 m in the longitudinal and transverse directions, respectively. The numerical method of FEM is correct based on the experimental validation, and can be used to identify the appropriate strengths of FPB shear pins for other railway bridges.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The present research aims to study the influence of the soil–structure interaction (SSI) and existence or absence of masonry infill panels in steel frame structures on the earthquake-induced pounding-involved response of adjacent buildings. The study was further extended to compare the pounding-involved behavior versus the independent behavior of structures without collisions, focusing much on dynamic behavior of single frames. The effect of SSI was analyzed by assuming linear springs and dashpots at the foundation level. The infill panels were modeled using equivalent diagonal compression struts. The steel frames were assumed to have elastic–plastic behavior with 1% linear strain hardening. The dynamic contact approach was utilized to simulate pounding between the adjacent buildings. Nonlinear finite element analysis was performed for two adjacent multi-story structures with four different configurations representing cases that can exist in reality. The seismic response of the studied cases generally emphasized that ignoring the soil flexibility and/or the contribution of the infill panels may significantly alter the response of adjacent structures. This may result in a false expectation of the seismic behavior of buildings exposed to structural pounding under earthquake excitation.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Masonry walls are particularly vulnerable against out-of-plane seismic actions. Steel tie-bars and crowing beams in reinforced masonry can prevent their overturning, but collapse may take place also by bending, leaf separation or disaggregation. Textile Reinforced Mortar (TRM) composites, comprising high strength fabrics and inorganic matrices, can be applied to effectively improve the seismic capacity of masonry load-bearing walls and infill panels. Nevertheless, a deeper knowledge on the dynamic response and ultimate capacity of retrofitted walls still needs to be gained before TRM systems can be confidently used in engineering practice. This work describes a shake table test carried out on two full-scale wall specimens, one made of regular tuff blocks and one of two leaves of rubble stones, subjected to seismic out-of-plane vertical bending. The walls were tested unreinforced, repaired and strengthened with TRMs and tested again. A unidirectional textile of ultra high tensile strength steel was used on the tuff wall, whereas a bidirectional basalt mesh was applied over the entire surface of the stone wall, with the addition of transversal steel connectors. The responses of the specimens before and after retrofitting are compared to show the improvement of acceleration and displacement capacity entailed by TRM retrofitting and the modification of deflection profiles, failure modes, damage development and dynamic properties. Test outcomes prove the effectiveness of TRM composites for the protection of existing masonry structures, including architectural heritage, in earthquake prone areas and provide information on the reliability of analytical predictions for seismic assessment.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Liquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure and soil dilatancy, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Such a change of state can be analysed by considering the soil as an equivalent visco-plastic material, characterized by an apparent viscosity (η) that changes during the cyclic loading. Following this approach, the authors analysed the results of some cyclic undrained triaxial tests carried out on reconstituted and undisturbed (frozen) specimens of sandy and gravelly soils in terms of apparent viscosity decay law (η-N〈sub〉cyc〈/sub〉), highlighting the relevance of η as physically based parameter for the correct identification of the liquefaction triggering. The experimental results confirm that the apparent viscosity decreases with the increase of the shear strain rate and highlight that the flow characteristics of liquefied soils (consistency coefficient and liquidity index) are affected by both grain size distributions and soil state conditions (relative density and confining stress).〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This study focuses on the seismic vulnerability of masonry buildings damaged by the 2009 L’Aquila earthquake. A geo-referenced database of 32,520 masonry residential buildings was compiled in the aftermath of the earthquake under the coordination of the Italian Department of Civil Protection through the AeDES survey form. The availability of this enormous amount of data provides an exceptional opportunity to examine in depth damage data and their correlation with the main parameters available from the post-earthquake survey. The original database was grouped into 20 building classes, defined as a function of vertical and horizontal structural types. Damage levels defined according to the European Macroseismic Scale classification are used to derive damage probability matrices and relevant vulnerability curves for these classes. The influences of connection systems, the quality/regularity of the masonry wall layout and the horizontal structural type on the building response are analysed in detail. A vulnerability classification, also supported by the use of statistical post hoc tests, is used to detect a reduced number of independent classes. The parameters of the non-crossing fragility curves are determined via the maximum likelihood estimation method by adopting a lognormal cumulative function to determine the exceedance probabilities of the considered damage levels. The impact of “mixed” classes, characterized by multiple vertical and/or horizontal structural types, on the derivation of the fragility curves is also investigated. Finally, the adaptation of the general version of the fragility curves to large-scale applications based on poor (census) data is also demonstrated, leading to curves that are easily usable in regional/national seismic loss assessments.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Sand liquefaction-induced lateral flow has caused the destruction of a large number of buildings. In this work, an overall time-history numerical simulation is conducted to study the nonlinear dynamic interaction of soil with an underground structure buried in a slightly sloping liquefied foundation. Firstly, the consistency between the numerical simulation and model test results is verified. Then, the influence law of the ground inclination angle on the liquefaction distribution of the foundation around an underground structure reveals that the soil liquefaction at the lateral side of the underground structure is alleviated but is aggravated severely in the soils under the subway station. Additionally, the dynamic uplifting behavior and the seismic damage of the underground structure are different from those in a horizontally layered liquefied foundation. The rotation response and asymmetrical seismic damage of an underground structure in a slightly sloping liquefied foundation need attention.〈/p〉

Beschreibung: 〈p〉The original article has been thus corrected with the corrected references and thus updated.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A bi-normalized Newmark–Hall response spectrum is presented for seismic design and assessment of structures. The period axis is normalized with respect to a characteristic period relating only to peak ground-motion parameters. The amplification factors are determined through a statistical analysis by normalizing spectral pseudo-acceleration, spectral pseudo-velocity, and spectral displacement, relative to peak ground acceleration, peak ground velocity, and peak ground displacement, respectively, in the low-, intermediate-, and high-period ranges, which do not need to be prescribed prior to normalization. A total of 671 three-component accelerograms are selected from the New Zealand Strong Motion Database for the statistical analysis. The relationship between peak ground-motion parameters is studied, enabling the construction of a design spectrum from either a given design scenario earthquake, or a code-specified peak ground acceleration value.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Nonstructural components (NSCs) housed in building structures are subject to semi-narrow band excitations generated via filtering of the ground motion by the supporting building. NSC design forces are generally provided based on adopting a 5% NSC viscous damping ratio (〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉), whereas recent experiments illustrate that typical NSCs may exhibit 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉 values substantially different, mostly lower, than 5%. This study introduces damping modification factors (DMFs) to adjust NSCs elastic seismic design forces for other 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉 values. Elastic floor spectra with different 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉 values are developed for floor motions obtained from several code-based designed buildings subjected to ground motion sets with different intensities. Numerical analyses illustrate that due to the narrow-band characteristic of building floor motions, applying conventional DMFs proposed for adjusting ground spectral ordinates may lead to the underprediction of floor spectral ordinates up to 55% for the range of 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉 evaluated in this study. Assuming a value of 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉, the amplitude of the DMF for a building floor spectrum is primarily a function of the NSC tuning ratio. For example, for a given floor motion and a 〈span〉 〈span〉\( \xi_{\text{C}} \)〈/span〉 〈/span〉 value of 2%, the DMF can vary from 1.0 (for a non-tuning condition) to 1.6 (for a tuning condition). To a lesser extent, the DMF is also influenced by supporting building characteristics (e.g., the level of inelastic behavior, fundamental period, height, and lateral-force resisting system), the vertical location of the NSC in the building, and ground excitation characteristics. Practical expressions, which are developed through simple modifications of the prescribed ground spectra DMFs by ASCE/SEI 41-13, are proposed to estimate DMFs for elastic floor spectra.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The assessment of maximum displacement demand is a crucial point in the design of seismic isolating systems, in particular when the non linear behaviour of devices is modeled through visco-elastic equivalent schemes, as common in the design practice. Several phenomena influence the maximum demand assessment, among which the torsional and earthquake directionality effects can be of great impact. International codes use some formulations which allow to consider torsional effects, while the impact of the other phenomena is commonly assessed through time-history analyses. In this paper an innovative design method is developed based on an exact linear elastic formulation with response spectrum, which keeps in count both torsional and directivity effects considering natural and accidental eccentricity and by using the CQC3 (Menun and Der Kiureghian in Earthq Spectra 153–163, 〈span〉1998〈/span〉. 〈span〉https://doi.org/10.1193/1.1586025〈/span〉) as directional combination rule. The method models the seismic action through the response spectra of a set of natural recorded ground motions, properly oriented along their principal axes to assess the correct ratio between the horizontal components of spectral accelerations; thus accounting for the site-specific earthquake source, without the need to perform time-history analyses. A specific formalization of the dynamic problem is presented to emphasize the parameters which more affects the response (e.g. torsional factor, eccentricity, geometrical aspect ratio) and simplify its interpretation. Results obtained on two case studies are compared with time-history analyses to show the effectiveness of the procedure.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A review study is presented targeting the question how topographic amplification of strong earthquake ground motions is currently handled in literature and how this effect can be incorporated within earthquake loss estimation (ELE). An improved understanding of the phenomenon would also facilitate its inclusion in future building design code provisions in a more rigorous manner than present levels. Even though it is widely accepted that, in addition to soil conditions, surface topography can have considerable influence on the frequency and amplitude characteristics of earthquake ground motion, this effect has been neglected in all of the existing ELE software tools, and neither do ELE studies in general consider this effect. Therefore, after a detailed review of the existing literature, we have synthesized the results from some of the studies into a period-dependent topographic amplification relationship (including PGA) for sites at the top of a hill, which may be used in ELE studies. The relationship for an amplification factor, 〈em〉A〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉, was obtained by fitting a database containing 333 data points, in which 〈em〉A〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉 ranges from 0.31 to 3.04, and the shape relief (〈em〉H〈/em〉/〈em〉L〈/em〉) ranges from 0.25 to 0.8. Out of these, seven data points correspond to topographic amplification of PGA while the remaining data points correspond to amplification of the spectral acceleration at periods ranging between 0.065 and 3.91 s. All the data stems from analytical/numerical studies and we have only considered the possibility of topographic amplification due to SV/SH waves with an incidence angle perpendicular to the base of the hill. The results show a reasonable correlation between the theoretical and the fitted data. We also have compared the amplification factors provided by our period-dependent relationships with the most recent experimental and numerical data for the Narni ridge (Italy) and found close similarities with these results. The proposed relationship can be used not only in ELE studies but also in simplified seismic microzonation studies.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This paper proposes a set of new Bayesian regression models to perform first order reliability method (FORM) calculations of repair cost exceedance probability. The models are classified in two categories, story-specific demand model and consequence models. The demand model developed in the form of linear equation predicts maximum acceleration and drift at each story of low-to mid-rise regular steel moment resisting frames. The consequence models are formulated as polynomial functions based on output provided by the upstream demand model and estimate repair cost of 30 building fragility groups. Next, the application of the proposed models in a first order reliability analysis to compute seismic loss probabilities for some example buildings is evaluated. The results are compared with those of a FEMA P-58 full simulation-based analysis and the computation reduction provided by utilization of the proposed regression models in the context of the FORM is assessed. Based on this finding, the practically appealing potential of the developed models is shown.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉 The Groningen gas field is one of the largest in the world and has produced over 2000 billion m〈sup〉3〈/sup〉 of natural gas since the start of production in 1963. The first earthquakes linked to gas production in the Groningen field occurred in 1991, with the largest event to date being a local magnitude (M〈sub〉L〈/sub〉) 3.6. As a result, the field operator is leading an effort to quantify the seismic hazard and risk resulting from the gas production operations, including the assessment of liquefaction hazard. However, due to the unique characteristics of both the seismic hazard and the geological subsurface, particularly the unconsolidated sediments, direct application of existing liquefaction evaluation procedures is deemed inappropriate in Groningen. Specifically, the depth-stress reduction factor (r〈sub〉d〈/sub〉) and the magnitude scaling factor relationships inherent to existing variants of the simplified liquefaction evaluation procedure are considered unsuitable for use. Accordingly, efforts have first focused on developing a framework for evaluating the liquefaction potential of the region for moment magnitudes (〈strong〉M〈/strong〉) ranging from 3.5 to 7.0. The limitations of existing liquefaction procedures for use in Groningen and the path being followed to overcome these shortcomings are presented in detail herein.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉We present simulations performed for the development of a ground motion model for induced earthquakes in the Groningen gas field. The largest recorded event, with 〈strong〉M〈/strong〉3.5, occurred in 2012 and, more recently, a 〈strong〉M〈/strong〉3.4 event in 2018 led to recorded ground accelerations exceeding 0.1 g. As part of an extensive hazard and risk study, it has been necessary to predict ground motions for scenario earthquakes up to 〈strong〉M〈/strong〉7. In order to achieve this, while accounting for the unique local geology, a range of simulations have been performed using both stochastic and full-waveform finite-difference simulations. Due to frequency limitations and lack of empirical calibration of the latter approach, input simulations for the ground motion model used in the hazard and risk analyses have been performed with a finite-fault stochastic method. However, in parallel, extensive studies using the finite-difference simulations have guided inputs and modelling considerations for these simulations. Three approaches are used: (1) the finite-fault stochastic method, (2) elastic point- and (3) finite-source 3D finite-difference simulations. We present a summary of the methods and their synthesis, including both amplitudes and durations within the context of the hazard and risk model. A unique form of wave-propagation with strong lateral focusing and defocusing is evident in both peak amplitudes and durations. The results clearly demonstrate the need for a locally derived ground motion model and the potential for reduction in aleatory variability in moving toward a path-specific fully non-ergodic model.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A bespoke ground-motion model has been developed for the prediction of response spectral accelerations, peak ground velocity and significant duration due to induced earthquakes in the Groningen gas field in the Netherlands. For applications to the calculation of risk to the exposed building stock, extensions to the model are required. The use of the geometric mean horizontal component in the ground-motion predictions and the arbitrary horizontal component for the building fragility functions requires the addition of component-to-component variability. A model for this variability has been developed that both reflects the strong horizontal polarisation of motions observed in many Groningen records obtained at short distances and the fact that the strong polarisation is unlikely to persist at larger magnitudes. The other extension of the model is the spatial correlation of ground motions for the calculation of aggregated risk, which can be approximated through simple rules for sampling the variance within site response zones. Making use of ground-motion recordings from several networks in the field and the results of finite difference waveform simulations, a Groningen-specific spatial correlation model has been developed. The new model also combines results from traditional variogram fitting approaches with a new method to infer spatial correlation lengths from observed variance reduction. The development of the new spatial correlation model relaxes the need to approximate spatial correlation through the sampling of site response, although the results obtained herein suggest that similar results could be obtained using either approach. The preliminary consideration of the numerical waveform modelling results in this study paves the way for significant extensions to be made for the modelling of spatial correlations and the decomposition of apparent spatial variability into systematic and random components within a fully non-ergodic framework .〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Gas extraction in the Groningen Province in the Netherlands has caused seismicity. A method was needed for probabilistic assessments of the seismic performance of the levees that protect low-lying polders against flooding. By combining the First Order Reliability Method with response surfaces it proved possible to strongly reduce the required number of simulations with advanced numerical models to obtain reliable failure probability estimates. To illustrate the workings of the method, an application to a levee cross-section along the Eemscanal with a sheet pile wall is presented. The probabilistic method can be used for probabilistic assessments and the probability-based calibration of partial factors, and it could serve as a starting point for quantitative risk analyses for levee systems in earthquake prone regions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉We present a probabilistic framework to assess induced seismicity hazard and risk, while accounting for temporally-varying seismicity rates. The framework is based on the probabilistic seismic hazard assessment and risk assessment that are used extensively for tectonic earthquakes. Dynamic estimates of earthquake rates are produced using a Bayesian change-point approach. The risk framework combines hazard with vulnerability of the exposure and is implemented at a regional level. We implement a stochastic Monte Carlo based approach for our hazard and risk assessments using OpenQuake-engine. We present an application of the framework for Oklahoma, employ a ground-motion prediction equation applicable for the state and perform regional risk assessment for repair cost on the entire state. We also perform sensitivity studies on hazard and regional risk assessments for impacts of earthquake activity rate, magnitude distribution, ground-motion prediction equations and exposure vulnerabilities. Regional risk quantification can support regulators and operators in developing effective risk mitigation measures, and the sensitivity analyses help decision-makers perform cost-benefit analyses of their decisions and are beneficial for prioritization of further research.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In recent years, gas extraction in the northern part of the Netherlands has been causing low-magnitude, induced, shallow earthquakes. Besides safety, the prediction and evaluation of ‘light’ damage due to these induced ground motions is important, as it is related to economic and serviceability losses, and societal unrest. An experimental and numerical campaign is ongoing at Delft University of Technology, aiming to improve the knowledge of the underlying physics of crack initiation and propagation in unreinforced masonry (URM) structures typical in the Netherlands. A damage scale and damage parameter are defined herein in order to objectively quantify cracking damage as a function of the number, length, and width of cracks in masonry walls. The cracking mechanisms are studied for URM walls and spandrels subjected to in-plane loading. Displacements, strains, and loads under which cracking starts and propagates are evaluated and correlations are sought. The Digital Image Correlation measuring system is used to accurately detect crack formation and the evolution of the cracking pattern. This is also utilised to validate and calibrate non-linear finite element models. From the experiments, drift values are obtained for the light damage state of the masonry walls. A range between 0.3‰ and 1.1‰ is set as belonging to light damage. Moreover, a damage accumulation or material degradation was observed during cyclic testing. Additionally, fracture-mechanics based, micro and macro finite element models are capable of reproducing the repetitive behaviour of the tests.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The reliability of a risk assessment procedure is strictly dependent on the adopted hazard, exposure, fragility and consequence models. This paper presents the methodology adopted to support the assessment of the seismic vulnerability of buildings in the Groningen province of the Netherlands by means of a comprehensive in situ and laboratory testing programme. The area, historically not prone to tectonic ground motions, experienced seismic events induced by gas extraction and subsequent reservoir depletion in the last decades. The peculiarity of the input ground motions, the distinctive features and a general lack of knowledge on the seismic response characteristics of the Dutch building stock, and the goal to also assess the collapse risk drove the design and execution of a comprehensive test campaign comprising in situ tests and full-scale shaking table tests of buildings. An overview of the whole campaign is presented, focusing on the merits and roles of the different experimental techniques. The main outcomes of the experimental tests are summarized and additional and wider research findings together with potential research avenues for future studies are also identified.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The slab spatial composite effect plays a significant role in the seismic behaviour of composite frame structures. In this work, the influence of the slab spatial composite effect on the dynamic behaviour of composite frame structures was numerically studied. The self-developed fibre beam–column element program COMPONA-MARC was used to establish models considering and neglecting the slab spatial composite effect for nonlinear static analysis and elastic–plastic time history analysis under various seismic inputs. The maximum roof displacement, inter-storey drift ratio, normalised displacement indices, deformation mechanism, and failure mode were considered to investigate the structural performance. Comparisons indicated that, despite the contributions of the slab spatial composite effect to the structural lateral strength and stiffness, considering this effect may produce more unsafe results. On one hand, it reduces the fundamental natural vibration period and amplifies the effect of seismic excitation; on the other hand, it changes the structural deformation mechanism and failure mode. The influence of slab spatial composite effect on strong column–weak beam mechanism in different storey drift direction angles is also investigated in the paper.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The objective of this study is to determine the effects of near-fault ground motions with large, medium and small pulse periods on a core-wall tall building. Three near-fault and one far-field ground motion sets, each with 11 different records, are rotated to the maximum pseudo-velocity spectrum directions. The mean transition periods of each set are obtained by the smoothed tripartite spectrum, which illustrates that the acceleration–sensitive region extends with increasing pulse duration. A 40-story core-wall building is subjected to 44 different record pairs, and the analysis results show that the ratio of pulse duration to first mode period (T〈sub〉p〈/sub〉/T〈sub〉1〈/sub〉), governs the nonlinear response. It is demonstrated that higher mode effects increase while the first mode sensitive region moves away from the second mode sensitive region. The distribution profiles of the story drift, tension strain, and beam rotation demands along the height of the building are substantially different depending on the T〈sub〉p〈/sub〉/T〈sub〉1〈/sub〉 ratio. In the large and medium pulses records, the core-wall reaches the flexural yielding capacity above the podium level, and this phenomenon increases the story drift ratio and flexural beam rotation demands depending on the displacement demands at the end of the acceleration-sensitive region. On the contrary, near-fault with small pulses and far-field ground motions induce yielding of core-wall at upper stories due to higher mode effects. Thus, post-yield story shear force distributions significantly change compared to the large and medium pulses ground motions.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This work mainly aims to propose a new design procedure combining the benefits of the Performance-Based Plastic Design approach (PBPD) with a rigorous accounting of second-order effects. In fact, by exploiting the kinematic theorem of plastic collapse, second-order effects can be accounted for employing the concept of collapse mechanism equilibrium curve. The same tool constitutes the base of the Theory of Plastic Mechanism Control (TPMC) design approach. Besides, the paper reports a critical comparison between TPMC and PBPD, both having the scope to design structures exhibiting a collapse mechanism of global type. These two approaches are also compared with the refined PBPD where second-order effects are accounted for by the kinematic approach. Many steel moment resisting frames are designed according to PBPD, TPMC and refined PBPD and their performances have been compared on the bases of push-over analyses.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉In May 2012, a series of medium–high intensity earthquakes struck a highly industrialized area of central-northern Italy and in particular the Emilia-Romagna region. As a consequence, there were 28 casualties, numerous injuries, and vast damage to thousands of civil structures, infrastructures and industrial facilities. After that, the regional political authority, Regione Emilia-Romagna, spent billions of euro of state funding on reconstruction; as of 2018, almost EUR 1.9 billion was granted to business sector. In order to be able to fairly distribute financial aid to damaged productive facilities, a vast information system was created and data were stored in a database called SFINGE. Collected information regards losses, induced costs, reimbursements paid by the insurance companies, and money finally granted by the state. In this paper, we present the results of a study we conducted on the database; the requests for public funding were accessed and examined within a special scientific agreement between Regione Emilia-Romagna and RWTH Aachen University. Study results will be useful in predicting costs, economic losses and insurance refunds for business activities damaged by seismic events. Public authorities can learn too, as the paper presents a way of accounting consequences and granting public money that proved to work effectively. Finally, reported data can be included within the existing theoretical framework of Performance Based Earthquake Engineering, significantly contributing to the definition of seismic performance assessment tools.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Seismic events that struck Italy in the last years had a dramatic impact on historical and cultural heritage. Damage occurred on existing masonry buildings, in particular on churches, stressed out the need to better understand the seismic behaviour of this type of constructions as well as to define more appropriate mitigation strategies to be applied at large scale. This study deals with a predictive methodology for vulnerability assessment of churches in large territorial areas. Focusing the attention on three naves churches of Abruzzi, the paper proposes modifications and integrations of an existing methodology taken by literature. These modifications are defined through a calibration procedure based on damage observation of 64 three naves churches located at different distances from the epicentre of the 2009 earthquake. The proposed model is employed to predict damage level distribution for different earthquake intensities, allowing fragility curves to be plotted and therefore potential damage scenarios to be represented.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉As a result of changes in seismicity in the Groningen area, a need has arisen to be able to rapidly assess and prioritize entire inventories of unreinforced masonry churches. As a part of being able to provide resource optimization to determine which structures are in most need of intervention, a multilevel methodology to assess seismic performance is presented. The process involves both data collection and vulnerability assessments. This multilevel approach involves progressive refinements to the data collected and to the complexity of the analyses conducted. Five data collection phases are used in conjunction with three progressively more complex methods for the seismic assessment. The first level of assessment uses only statistical information of the structures with information that can be obtained through desktop reviews. The second level of analysis uses key characteristics of wall thickness and height to develop simple models for each wall in each church. This level of analysis requires at least a preliminary site visit. In the third level of analysis, a more refined model of the church is developed from detailed site surveys of the structure where each wall is modelled and assessed. The process involves the assessment of the in-plane behaviour of either whole churches or single walls (global response) and the out-of-plane behaviour of single elements (local response). The study applies the approaches outlined in the NEN NPR9998 2017 combined with the Italian Standards for the cultural heritage. This paper outlines this Seismic Multilevel Assessment of Churches methodology and how it applies to an inventory of 52 unreinforced masonry churches in the Groningen area, The Netherlands.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The post-earthquake damage assessment represents the first step after an emergency to support not only the safety of people, but also the preservation of buildings through the realization of prompt and effective provisional interventions. The issue is of particular relevance in case of monumental assets such as churches that are the focus of the paper. In Italy, since 1997 the post-earthquake damage assessment of churches has been carried out using a specific form, which was formally approved in 2001 by the Italian Civil Protection. Being the most advanced tool available in the literature within this specific field, the Italian form has been widely used also internationally. It follows the approach based on the decomposition of the church into macroelements. Although the latter has found wide confirmation through the interpretation of real damage, some critical issues were raised in relation to the versatility of the form and the reliability of the damage index that the approach provides. The post-earthquake damage assessment of 48 unreinforced masonry churches located in New Zealand, hit by the Canterbury earthquake sequence 2010–2011, represented an unprecedented opportunity, at international level, to investigate and to address the aforementioned issues. Starting from some weaknesses of the actual form, a new proposal (named 〈em〉CAF〈/em〉-〈em〉D〈/em〉) for the damage assessment of unreinforced masonry churches has been developed and presented in the paper. The new form is still based on the macroelement approach, but it considers, in a separate way, the macroelements and the seismic damage modes they might develop, thus overcoming the limitation of the fixed number of damage mechanisms identified 〈em〉a priori〈/em〉 by the current Italian form. The more reliable damage assessment approach that such form aims to achieve is the prelude to the development of a specific vulnerability model, derived by combining an empirical and an expert elicitation approach. A specific vulnerability model developed for New Zealand churches, derived by implementing the proposed 〈em〉CAF〈/em〉-〈em〉D〈/em〉 form and the related damage assessment procedure, is presented in the last part of the paper.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉It is generally known that reinforced concrete frame structures with unreinforced masonry infills frequently suffer severe damage when subjected to earthquake loading. Recent earthquakes show that the damage occurs to both older buildings and new seismically designed buildings. This is somehow surprising as this construction type has been the subject of intensive research projects for decades and simplified verification concepts are available in standards. However, these concepts are based on the separate verification of in-plane and out-of-plane loading although the importance of the design for combined loading conditions is already known. This situation was the reason to perform comprehensive investigations of the seismic behaviour of this traditional construction type for separate and combined in-plane and out-of-plane loading within the framework of the collaborative European research project INSYSME (Innovative systems for earthquake resistant masonry buildings in reinforced concrete buildings). These investigations are helpful to develop innovative approaches to improve the seismic behaviour of infilled frames. This article presents the fundamental project results of experimental investigations on reinforced concrete frames filled with high thermal insulating clay bricks under separate, sequential and combined in- and out-of-plane loading. The test results clearly illustrate that the load-bearing capacity severely depends on the boundary conditions in the connection area between the infill and the frame.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Iceland is seismically the most active region in northern Europe. Large single earthquakes (~ 〈span〉 〈span〉\( M_{\text{w}} \)〈/span〉 〈/span〉 7) and seismic sequences of moderate-to-strong earthquakes (~ 〈span〉 〈span〉\( M_{\text{w}} \)〈/span〉 〈/span〉 6–6.5) have repeatedly occurred during past centuries in the populated South Iceland Seismic Zone (SISZ). The seismic hazard in Iceland has mainly been evaluated using ground motion models (GMMs) developed from strong-motion observations in other countries and only to a very limited extent from Icelandic data, despite a particularly rapid attenuation of ground motions with distance in Iceland. In this study, we evaluate the performance of these GMMs against the Icelandic strong-motion dataset, consisting of peak ground accelerations of moderate-to-strong (〈span〉 〈span〉\( M_{\text{w}} \)〈/span〉 〈/span〉 5–6.5) and local (0–80 km) earthquakes in the SISZ. We find that these GMMs exhibit both a strong bias against the dataset and a relatively large variability, which calls their applicability and earlier hazard analyses into question. To address this issue, we recalibrate each of the GMMs to the dataset using Bayesian regression and Markov Chain Monte Carlo simulations. This approach allows useful prior information of the GMM parameters to be combined with the likelihood of the observed data and provides posterior probability density functions of model residuals and regression parameters. The recalibrated GMMs are unbiased with respect to the data and have a low total standard deviation of around 0.17 (base-10 logarithmic units). The model-to-model variability in the median predictions vary primarily with distance, reaching 0.05 the lowest for 〈span〉 〈span〉\( M_{\text{w}} \)〈/span〉 〈/span〉 6.3–6.5 at intermediate distances. While the lack of near-fault and far-field data, particularly at large magnitudes, and the different functional forms of the GMMs calibrated to the same dataset may affect the results, the recalibrated GMMs should represent well the ground motions of a typical sequence of moderate-to-strong SISZ earthquakes. We present the recalibrated GMMs of this study as promising candidates for future use in ground motion prediction in Iceland e.g., in the context of either a logic tree or the backbone approach in probabilistic seismic hazard assessment.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This article presents a comprehensive study of dynamic soil properties [namely, initial shear modulus-〈em〉G〈/em〉〈sub〉〈em〉max〈/em〉〈/sub〉; normalized shear modulus reduction (〈em〉G〈/em〉/〈em〉G〈/em〉〈sub〉〈em〉max〈/em〉〈/sub〉); and damping ratio (〈em〉D〈/em〉) variation curves] and pore water pressure parameters of a river bed sand (Brahmaputra sand), sampled from a highly active seismic region (northeast India). Two independent high quality apparatus (resonant column-RC and cyclic triaxial-CTX) are adopted in the study. Resonant column apparatus was used to obtain the small strain properties (up to 0.1%) while CTX equipment was adopted to obtain the high strain properties along with the pore water pressure parameters. The results obtained from both the equipment are combined to provide a comprehensive data of dynamic soil properties over wide range of strains. A modified hyperbolic formulation was suggested for efficient simulation of 〈em〉G〈/em〉/〈em〉G〈/em〉〈sub〉〈em〉max〈/em〉〈/sub〉 and 〈em〉D〈/em〉 variations with shear strain. Based on the CTX results, a pore water pressure generation model is presented. Furthermore, a nonlinear effective stress ground response study incorporating the pore water pressure generation, is performed using the recorded earthquake motions of varying peak bed rock acceleration (PBRA) in the region, to demonstrate the applicability of proposed dynamic soil properties and pore pressure parameters. High amplification for low PBRA ground motions (〈 0.10 g) was observed and attenuation of seismic waves was witnessed beyond a PBRA of 0.10 g near the surficial stratum due to the induced high strains and the resulting high hysteretic damping of the soil. Also, increased excess pore pressure generation with increased PBRA of the input motion was observed and the considered soil stratum is expected to liquefy beyond a PBRA of 0.1 g. The established properties can be handy to the design engineers during seismic design of structures in the northeast Indian region.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The simple lateral mechanism analysis (SLaMA) is an analytical method to assess the force–displacement capacity curve of Reinforced Concrete (RC) structures composed of frames, cantilever walls or dual wall/frame systems. The current version of the method was proposed in the 2017 New Zealand guidelines for the seismic assessment (NZSEE in New Zealand Society for Earthquake Engineering, the seismic assessment of existing buildings—technical guidelines for engineering assessments, Wellington, 〈span〉2017〈/span〉). Regarding frame structures, the possible influence of infill walls is currently considered locally with checks on the RC members. However, it is universally known that infills have a major effect on the global capacity curve of the frame. In this paper, a comprehensive SLaMA method for infilled frames is proposed, which allows considering the influence of the infills on the global force–displacement curve without any numerical algorithm. The extended SLaMA method is herein formalised and it is validated in a companion paper (part 2) through an extensive parametric analysis. The extended SLaMA is based on the possibility to separately calculate the base shear contributions of the frame and the infills, in turn based on global equilibrium considerations. Such considerations also allow defining a novel procedure to post-process the results of pushover or time-history analyses where infills are modelled as diagonal struts, or to interpret experimental tests. This allows, within a single numerical analysis, to decouple the frame and infills contributions to the base-shear capacity. The decoupling procedure is herein demonstrated for an ideal two-storey, one-bay masonry-infilled frame with different infills configurations.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The need for proper nonlinear modelling of the structural damage resulting from strength and stiffness degradation observed at different levels of seismic intensity is essential in a comprehensive response assessment of a structural system. A nonlinear model based on plastic and damage mechanisms is presented here for seismic analysis of inelastic structures. To begin with, piecewise linearization of the initial backbone curve is carried out, each segment being defined by an in-parallel combination of elastic-perfectly plastic and elastic-softening damage mechanisms. The deterioration of the plastic and damage mechanisms is controlled by a damage index, which involves an accumulation rule of a damage parameter. Then, simulation of structural components is used to exemplify the reproduction of some hysteretic models with different types of degradation. Comparison with experimental results is subsequently carried out to calibrate the proposed model. Cyclic histories, with variable amplitude, are also considered to illustrate the effects of the plastic-damage mechanisms on the hysteretic response. Finally, nonlinear seismic analysis of a single-degree-of-freedom system, equivalent to an r.c. framed structure, is used to highlight the capability of the proposed approach in order to generate the capacity boundary curve starting from the initial backbone curve.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Previous studies on the seismic behaviour of precast segmental concrete column revealed that concrete crushing and spalling damages may occur at the toes of the segments due to rocking between segments at the joints. In addition, the energy dissipation capacity of segmental column is smaller than the conventional monolithic column. Energy dissipation bars therefore have been proposed to increase its energy dissipation capability, which, unfortunately, at the cost of also increasing the residual displacement of the column, hence degrades the most advantageous characteristic of precast segmental column. To solve these problems, this paper proposes wrapping the segments with basalt fibre-reinforced polymer (BFRP) to reduce the concrete compressive damage and tension-only external energy dissipation (TEED) devices to dissipate energy without substantially increasing the residual displacement. Experimental cyclic tests and numerical simulations are carried out to examine the effectiveness of the proposed method. The results show that the damage of the segments could be effectively reduced by using BFRP, and the columns show good ductility and almost no strength degradation. The TEED devices are effective to increase the energy dissipation capacity of the column without significantly increasing the residual displacement.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Current seismic design of buildings is mostly based on applying earthquake excitation along principal (reference) axes of the building plan and response assessment on the same axes. However there is a challenge, whether or not the seismic excitation is applied on the principal axes, critical responses can take place on non-principal directions. The compound of this challenge with inherent response complexity in nonlinear behaviour of plan-irregular buildings leads to critical responses whose estimation is complicated. Current study proposes a new approach to address these challenges by presenting a 3-dimensional perspective for drift, ductility and damage indices. The concept of spatial response distributions is developed wherein vertical and planar response variations can be assessed. 4-, 8- and 12-storey reinforced concrete moment-frame structures with a typical L-shaped plan are employed in multi-direction pushover and nonlinear response history analyses, using 60 record component pairs of near-field and far-field earthquakes. Based on nonlinear regression analysis, several combination rules and amplification factors are derived for the critical responses polarized on non-principal directions at each storey level. A substantial increase (20%-to-60%) in the responses is observed; it depends on seismic orientation scheme, vertical distribution and planar direction of interest, and response definition.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The scope of this study is the quantification of vertical peak floor acceleration demands at column lines and along the length of beams of elastic moment-resisting steel frames subjected to recorded ground motions. These demands correlate with the maximum strength demands on rigid nonstructural components attached to a frame structure. Since it is commonly assumed that buildings behave flexibly in the horizontal direction and rigidly in the vertical direction, the assessment of vertical acceleration demands is typically not considered in most cases. The results of this study show that vertical peak floor accelerations can be up to five times larger than the vertical peak ground acceleration, in contrast to horizontal peak floor accelerations that are only up to two times larger than the horizontal peak ground acceleration for the numerical models used in this study. The most significant amplifications estimated in the vertical direction are found at the center of the girders. Further investigations of modified steel frames indicate that the story-wise mass distribution has an influence not only on the vertical acceleration demand, but also on the horizontal component of the response, though to a lesser degree. In contrast, the response in the vertical and horizontal direction is only slightly affected by an increase in the flexural stiffness of the beams. The results of this study strongly indicate that in steel frames it can be considered highly questionable to ignore the amplification of the vertical acceleration component along the height of the structure.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Present study introduces two concepts for direct estimation of P-delta effect in both, strength based, and displacement based design methods. Although various previously conducted studies focused on inclusion of P-delta effect into the aforementioned design methods, development of reliable procedures is still attractive. The major argument of present study is that: treatment of P-delta effect can be enhanced by using an alternative response/design spectrum. To this end, and based on period-dependence feature of stability coefficient (SC), the “stability coefficient response spectra” (SCRS) is introduced. The SCRS, plots spectral acceleration versus SC, instead of period, for a pendulum with known height. To facilitate implementation of SCRS on multi-degree-of-freedom systems, and by considering some special features of the first-storey, the concept of “first-storey-single-degree-of-freedom” (FSSDOF) system is introduced. The FSSDOF system permits setting the minimum necessary lateral stiffness, conforming to a pre-selected SC limit, and a given ductility level, at very early stages of design process. Moreover, it is shown that implementation of SCRS and FSSDOF system can be extended to account for drift limits. This is done by introducing a modified version of the “yield-point-spectra” method in which period-dependence feature of SC is recognized. Several numerical examples are included as part of the presentation.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉This study proposes a self-centering brace that can be easily assembled. It incorporates disc springs and friction pads to provide recentering force and energy dissipation, respectively. To analyze the hysteretic behavior of the assembled self-centering brace (ASCB), a hysteretic model based on the working mechanism of the ASCB is proposed. A modified Bouc–Wen model is developed to predict the behavior of the brace. A 1.336 m ASCB was designed and fabricated, and its hysteretic behavior was evaluated by cyclic testing. Results shows the full flag-shaped response of the ASCB and confirms the validity of the modified Bouc–Wen model. Fatigue and destructive tests verifies the stability of recentering and energy dissipation behaviors under cyclic loading with large axial deformation. After 50 cyclic loadings with an axial deformation ratio of 1.1%, the hysteretic behavior of the brace is stable, and the change in the maximum axial force is less than 4.2%. When the loading deformation ratio exceeds 2.0%, the brace fails because of overall buckling.〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Dynamic analyses of piles subjected to both vertical and horizontal loading under seismic conditions are of great significance to geotechnical and practicing engineers and the numerical methodology proposed in the present study fills the existing research gap. A finite difference based computer program FLAC3D is used to model a single pile and obtain the deflection and bending moment behaviour along the depth of the pile, under earthquake loading conditions in both non-liquefiable and liquefiable soil. The various earthquake motions considered in the current analysis includes 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj and 2011 Sikkim motions The bending moment is maximum at the interface of the liquefying and non-liquefying soil layers due to shear strain in the soil being discontinuous across the interface of the layers. The free field ground surface displacement is observed to initially increase with time, reaching the maximum at some instant during shaking and thereafter it remains constant with time, due to local failure of the liquefiable soil around the pile foundation. The combination of vertical load and lateral load on the pile top is varied to obtain the P-delta curves under dynamic loading conditions which are important factors for peak pile bending moment, when there is lateral spreading due to liquefaction causing displacement of the pile head, and inertial load from the superstructure is present. Hence a thorough evaluation of both horizontal and vertical inertial interactions and kinematic interactions due to free field motions, is necessary for considering the behaviour of piles in liquefiable soil and under combined loading situations.〈/p〉