ALBERT

Description: In the paper, five procedures for the assessment of the seismic performance of low-rise RC buildings at different levels of complexity are presented and discussed. They include simple procedures based on methods originally developed in Japan (levels 1 and 2), the N2 method with two variants of the mathematical model (levels 3 and 4), and non-linear dynamic analysis (level 5). The procedures have been applied to seismic assessments of three RC building structures. A small difference between the N2 and NDA results was observed, whereas the results of the procedures at the first two levels are much more conservative. On the other hand, the amount of input data and of computational work increases with the increasing complexity level. Research is still needed on the definitions of capacities, especially the shear capacity of the structural members, and on the capacity of the whole structure. The initial effective stiffness of the structure proved to be the most important quantity which determines the seismic demand.

Description: In many countries such as Spain earthquake databases still mainly comprise macroseismic data from felt effects. The full exploit of this information is of basic importance for seismic risk assessment and emergency planning, given the strict link between macroseismic intensity and damage. A probabilistic procedure specifically developed to handle macroseismic data, mostly relying on site information and seismogenic-source free, has been applied to evaluate seismic hazard in SE-Spain (Alicante-Murcia region). Present seismicity is moderate-low with largest magnitudes slightly over Mw5.0. The historical record includes very destructive earthquakes, maximum EMS98 intensities reaching IX–X and X in the nineteenth century (e.g., Torrevieja 1829 earthquake). Very recently, two events in the area on 11 May 2011 (Mw4.5, Mw5.2) killed nine people, injured 300, and produced important damage in the city of Lorca. Regional hazard maps for the area together with specific hazard curves at selected localities are obtained. Results are compared with the maximum observed intensities in the period 1300–2012, and with the values in the seismic hazard map from the Spanish Building Code in force. In general, the maximum felt intensity values are closer to the hazard values calculated for 2 % probability of exceedance in 50 years, using felt and expected intensity. The intensity-based probabilistic hazard maps obtained through the applied approach reduce the inherent smoothing of those based on standard probabilistic seismic hazard assessment approaches for the region, allowing identifying possible over- or sub-estimates of site hazard values, providing very valuable information for risk reduction strategies or for future updates of the building code hazard maps.

Description: Earthquake early warning systems (EEWSs) that rapidly trigger risk-reduction actions after a potentially-damaging earthquake is detected are an attractive tool to reduce seismic losses. One brake on their implementation in practice is the difficulty in setting the threshold required to trigger pre-defined actions: set the level too high and the action is not triggered before potentially-damaging shaking occurs and set the level too low and the action is triggered too readily. Balancing these conflicting requirements of an EEWS requires a consideration of the preferences of its potential end users. In this article a framework to define these preferences, as part of a participatory decision making procedure, is presented. An aspect of this framework is illustrated for a hypothetical toll bridge in a seismically-active region, where the bridge owners wish to balance the risk to people crossing the bridge with the loss of toll revenue and additional travel costs in case of bridge closure. Multi-attribute utility theory (MAUT) is used to constrain the trigger threshold for four owners with different preferences. We find that MAUT is an appealing and transparent way of aiding the potentially controversial decision of what level of risk to accept in EEW.

Description: Real-time hybrid simulation (RTHS) combines physical experimentation with numerical simulation to evaluate dynamic responses of structures. The inherent characteristics of integration algorithms change when simulating numerical substructures owing to the response delay of loading systems in physical substructures. This study comprehensively investigates the effects of integration algorithms on the delay-dependent stability and accuracy of multiple degrees-of-freedom RTHS systems. Seven explicit integration algorithms are considered; and the discrete-time root locus technique is adopted. It is found that the stability of RTHS system is mainly determined by the time delay rather than the integration algorithms, whereas its accuracy mainly depends on the accuracy characteristic of the applied integration algorithm itself. An unconditionally stable integration algorithm cannot always guarantee good stability performance; and the inherent accuracy or numerical energy dissipation of integration algorithms should be taken into account in RTHSs. These theoretical findings are well verified by RTHSs.

Description: Laboratory testing, although necessary to understand failure mechanisms of individual masonry walls, spandrels or small scale building models, cannot fully mimic the real system behavior of masonry structures. In order to observe the performance of an existing two story masonry structure, cyclic lateral load testing up to near collapse was conducted. The test building was sliced approximately in the middle through the reinforced concrete slabs of both stories and one side was strengthened with the objective of obtaining a strong reaction wall. The other side of the structure was taken as the test structure with a floor plan of approximately 10 m × 10 m. Hydraulic actuators attached at the slabs of both stories were employed to impose one way cyclic displacement excursions. Flexural and shear deformations on a number of walls were measured and crack propagations were monitored. The structure was tested up to a lateral strength drop of approximately 20 % from the ultimate load, which occurred at a drift ratio of about 0.60 %. The failure of the walls in the building, which were mostly failed in a diagonal tension mode, was concentrated on the first story. Results of this valuable test provide important data on the performance of an actual masonry building and were employed to assess the applicability of various stiffness and strength and simplified load-deformation models in the literature.

Description: Stability of isolation rubber bearings is a topic widely studied and concerns (1) the critical load capacity in the undeformed configuration, under long-term load (gravity) effects; and (2) the stability condition under short-term vertical pressure (due to gravity plus seismic loads) at large lateral deformations. In this paper the problem of elastomeric bearing stability under large lateral displacements is addressed through FEM parametric analysis; rubber bearings typical of current design practice, characterized by S 1  = 20 are considered, with the value of the secondary shape factor S 2 being varied between 1.5 and 6.2 in order to assess the effect of slenderness on the mechanical behavior, failure mode, and interaction vertical pressure–shear deformation. The analysis results show that the sensitivity of the shear response to the applied vertical pressure is directly related to the value of S 2 and that S 2 has an overwhelming effect on the stability behavior and shear response of the bearing, as compared to the effect of the primary shape factor and of the rubber shear modulus. Finally, S 2 is the parameter which governs the failure mode of the bearing in the seismic condition (vertical pressure–shear deformation). On the basis of these results, design implications are discussed.

Description: This paper presents a time-harmonic boundary element–finite element three–dimensional model for the dynamic analysis of building structures founded on viscoelastic or poroelastic soils. The building foundation and soil domains are modelled as homogeneous, isotropic, viscoelastic or poroelastic media using boundary elements. The foundation can also be modelled as a perfectly rigid body coupled to soil and structure. The buildings are modelled using Timoshenko beam finite elements that include the torsional eccentricity of non-symmetrical buildings. The excitation model includes far-field plane seismic waves of P, S or Rayleigh type for viscoelastic soils and P1 and S type for poroelastic soils. Modelling foundation and structure as rigid body and Timoshenko beam respectively conveys important benefits such as a significant reduction in the number of degrees of freedom in the problem, which allows to study problems involving several building structures and the interactions between them with acceptable computational effort. Results are presented for validation purposes first, and for studying the influence of modelling the soil as a viscoelastic or poroelastic region afterwards. Results involving structure–soil–structure interaction are also presented for illustration purposes.

Description: The evolution of the expected earthquake losses in different Portuguese regions was studied in order to determine whether the natural regeneration of buildings could contribute to the mitigation of seismic risk, although the building exposure has increased over time in most analysed regions. To achieve this goal, five inter-related risk indicators were estimated, based on the Portuguese censuses’ surveys of residential buildings and inhabitants obtained in two different moments in time: 2001 and 2011. The FEMA ( 2008 ) approach was used to estimate the risk indicators, i.e., the Annualized Economic and Human earthquake Losses, either in absolute terms or normalised by building and population exposure. This study offers a perspective of the seismic risk in the Portuguese mainland, provides a comparison of risk levels between different epochs, and analyses the obtained results in order to compare the risk among Portuguese regions. It is important to mention that the comparison of economic losses based on the building stocks surveyed in 2001 and in 2011 took into account the Portuguese inflation rate in that time interval. The main findings of the study show that the natural regeneration of the residential housing stock contributes to the reduction of the expected seismic economic losses in Portugal, at an average rate of 14 % per 10 years, and to the reduction of the expected annualized human losses to almost one half after 10 years. The results support the conclusion that the natural regeneration of the residential housing stock contributed to the mitigation of the seismic risk in mainland Portugal, in the 10 year period under analysis, even though there was an increase of the building exposure in the region.

Description: Nonstructural components (NSCs) should be subjected to a careful and rational seismic design, in order to reduce the economic loss and to avoid threats to the life safety, as well as what concerns structural elements. The design of NSCs is based on the evaluation of the maximum inertia force, which is related to the floor spectral accelerations. The question arises as to whether Eurocode 8 is able to predict actual floor response spectral accelerations occurring in structures designed according to Eurocode 8. A parametric study is conducted on five RC frame structures in order to evaluate the floor response spectra. The structures, designed according to Eurocode 8, are subjected to a set of earthquakes, compatible with the design response spectrum. Time-history analyses are performed both on elastic and inelastic models of the considered structures. Eurocode formulation for the evaluation of the seismic demand on NSCs does not well fit the numerical results. Some comments on the target spectrum provided by AC 156 for the seismic qualification of NSC are also included.

Description: Modelling seismic attenuation is one of the most critical points in the hazard assessment process. In this article we consider the spatial distribution of the effects caused by an earthquake as expressed by the values of the macroseismic intensity recorded at various locations surrounding the epicentre. Considering the ordinal nature of the intensity, a way to show its decay with distance is to draw curves—isoseismal lines—on maps, which bound points of intensity not smaller than a fixed value. These lines usually take the form of closed and nested curves around the epicentre, with highly different shapes because of the effects of ground conditions and of complexities in rupture propagation. Forecasting seismic attenuation of future earthquakes requires stochastic modelling of the decay on the basis of a common spatial pattern. The aim of this study is to consider a statistical methodology that identifies a general shape, if it exists, for isoseismal lines of a set of macroseismic fields. Data depth is a general nonparametric method for analysis of probability distributions and datasets. It has arisen as a statistical method to order points of a multivariate space, e.g., Euclidean space \({\mathbb {R}}^{p}\) , \(p \ge 1\) , according to the centrality with respect to a distribution or a given data cloud. Recently, this method has been extended to the ordering of functions and trajectories. In our case, for a fixed intensity decay \(\varDelta I\) , we build a set of convex hulls that enclose the sites of felt intensity \(I_s \ge I_0 -\varDelta I\) , one for each macroseismic field of a set of earthquakes that are considered as similar from the attenuation point of view. By applying data depth functions to this functional dataset, it is possible to identify the most central curve, i.e., the attenuation pattern, and to consider other properties like variability, outlyingness, and possible clustering of such curves. Results are shown for earthquakes that occurred on the Central Po Plain in May 2012, and on the eastern flank of Mt. Etna since 1865.

Description: Dissemination of knowledge should be a core objective for scientists who work with communities exposed to natural disasters. This task requires the spread of knowledge, to make the public aware in a simple, easy-to-understand, manner, yet without any loss of accuracy. ‘Urban Disaster Prevention Strategies using Macroseismic Fields and Fault Sources’ (UPStrat-MAFA) was a European project devoted to the implementation of strategies for urban disaster prevention of several aspects of seismic hazard, including the damage state and the earthquake impact. The project carried out numerous outreach activities for the public and stakeholders, to encourage the development of a bottom-up strategy towards disasters mitigation. Here we provide a description of actions that have been aimed at: (1) ensuring effective dissemination and communication of the project outcomes, also after its completion; and (2) raising public awareness and understanding in countries exposed to earthquake hazard.

Description: This study analyses the performance of residential buildings in the town of Hveragerði in South Iceland during the 29 May 2008 Mw 6.3 Ölfus Earthquake. The earthquake occurred very close to the town, approximately 3–4 km from it. Ground shaking caused by the earthquake was recorded by a dense strong-motion array in the town. The array provided high-quality three-component ground acceleration data which is used to quantify a hazard scenario. In addition, surveys conducted in the town in the aftermath of the earthquake have provided information on macroseismic intensity at various locations in the town. Detailed information regarding the building stock in the town is collected, and their seismic vulnerability models are created by using building damage data obtained from the June 2000 South Iceland earthquakes. Damage to buildings are then simulated by using the scenario hazard and vulnerability models. Damage estimates were also obtained by conducting a survey. Simulated damage based on the scenario macroseismic intensity is found to be similar to damage estimated from survey data. The buildings performed very well during the earthquake—damage suffered was only 5 % of the insured value on the average. Correlation between actual damage and recorded ground-motion parameters is found to be statistically insignificant. No significant correlation of damage was observed, even with macroseismic intensity. Whereas significant correlation was observed between peak ground velocity and macroseismic intensity, neither of them appear to be good indicators of damage to buildings in the study area. This lack of correlation is partly due to good seismic capacity of buildings and partly due to the ordinal nature of macroseismic intensity scale. Consistent with experience from many past earthquakes, the survey results indicate that seismic risk in South Iceland is not so much due to collapse of buildings but rather due to damage to non-structural components and building contents.

Description: This paper presents a case study on the influence of absence of floor slab constraints and large mass turbine as a non-conventional tuned mass damper (TMD) on the seismic behavior of the structure and members. The investigated structural system is a reinforced concrete (RC) shear wall-frame power plant structure with large slab openings and a large mass turbine. In RC structures, the existence of floor slabs can usually provide strong constraints on beams so as to greatly increase their bearing capacity. However, due to some special functional demands, large area of slabs may have to be removed so that some floor beams will lose the constraints provided by slabs. In such cases, beams could be subjected to complex internal forces and develop unexpected failure modes under earthquake actions. Nonlinear time history analyses are conducted by using the self-developed program COMPONA - MARC Version 1.0 . The numerical model employs fiber beam-column elements with distributed plasticity approach which can elaborately simulate the complex seismic behavior of structural members without slab constraints including the significant transverse vibration damage mechanism. For the seismic effectiveness of the turbine as a TMD with large mass ratio, the optimized parameters are discussed and verified by extensive numerical examples under a wide selection of ground acceleration time histories. The acceleration responses of the turbine are analyzed and found to satisfy the corresponding requirements. The dynamic interaction between the structure and turbine is evaluated and the effects of mass ratio and multiple supporting springs on the dynamic response of the turbine are investigated. It is found that the acceleration response of the turbine modeled with multiple supporting springs is evidently larger than that modeled with a single degree-of-freedom system, and the floor response spectrum decreases significantly with the increase of the mass ratio.

Description: This paper provides an investigation on the correlations between ground motion intensity measures (IMs) and engineering demand parameters (EDPs) through nonlinear dynamic analyses of MDOF systems under real earthquake recordings and then structural fragility curves are derived for the best correlated IM–EDP pairs. For this purpose, a parametric study on reinforced concrete (RC) buildings is carried out. Study buildings comprise 5-, 10-, 15- and 20-story, RC, code-complying, regular, moment-resisting frames designed for different strength reduction factors, e.g. R = 2, 4 and 6. The input ground motion dataset consists of 734 horizontal components of earthquake accelerograms. The best correlations between IMs and EDPs are computed by regression analysis. Sets of fragility curves in terms of maximum inter-story drift ratio, maximum plastic end rotation and maximum floor acceleration are derived based on log-normal distribution assumption. Fragility curves are presented not for a specific damage state such as slight, moderate etc. but for a range of damage thresholds on EDP.

Description: To comply with the need to spread the culture of earthquake disaster reduction, we rely on strategies that involve education. Risk education is a long-term process that passes from knowledge, through understanding, to choices and actions thrusting preparedness and prevention, over recovery. We set up strategies for prevention that encompass child and adult education, as a bottom-up approach, from raising awareness to reducing potential effects of disruption of society. Analysis of compulsory school education in three European countries at high seismic risk, namely Portugal, Iceland and Italy, reveals that generally there are a few State-backed plans. The crucial aspects of risk education concerning natural hazards are starting age, incompleteness of textbooks, and lack of in-depth studies of the pupils upon completion of their compulsory education cycle. Hands-on tools, immersive environments, and learn-by-playing approaches are the most effective ways to raise interest in children, to provide memory imprint as a message towards a culture of safety. A video game, Treme – treme , was prepared to motivate, educate, train and communicate earthquake risk to players/pupils. The game focuses on do’s and don’ts for earthquake shaking, and allows children to think about what might be useful in the case of evacuation. Education of the general public was addressed using audio-visual products strongly linked to the social, historical and cultural background of each country. Five videos tackled rising of awareness of seismic hazards in Lisbon, the area surrounding Reykjavik, Naples, and Catania, four urban areas prone to earthquake disasters.

Description: Earthquake-induced liquefaction of saturated soils continues to cause severe damage to structures with shallow foundations. In recent years, artificially reducing the degree of saturation and forming partially saturated zones within saturated soils has been proposed as a liquefaction mitigation technique. This study experimentally investigates the liquefaction response of air-injected partially saturated soils beneath shallow foundations. A series of centrifuge tests were conducted on the shallow foundations with different bearing pressures. The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation. Forming spatially distributed partially saturated zones in the liquefiable soils limited the development of high excess pore pressures and liquefaction susceptibility of soils, particularly at the higher confining stresses. The reduction in the degree of saturation of soils decreased the depth of liquefied soil layer, and increased the resistance of soil to the bearing capacity failure. On the other hand, the decrease in the degree of saturation of liquefiable soils led the larger accelerations to be transmitted to the foundations through unliquefied soil zones. It is therefore concluded that use of air-injection as a liquefaction mitigation measure does reduce structural settlements, but will have the consequence of larger structural accelerations.

Description: The paper deals with the behavior of restrained rocking blocks under seismic actions. Structural or non-structural masonry or r.c. elements, such as building façades or pre-cast panels subjected to out-of-plane modes, may be assimilated to rocking blocks restrained by horizontal springs. Horizontal restraints can represent flexible floors or steel anchorages or any anti-seismic device designed to impede overturning probability. Their effect could improve, in most cases, the dynamic response of blocks in terms of reduction of rotation amplitude. Nevertheless, this effectiveness could vanish or, surprisingly, affect the response in negative way, resulting in overturning when low values of stiffness or one-sided motion in particular conditions are assumed. Two cases of horizontal restraints are analyzed: (1) concentrated restraint as single spring and (2) smeared restraint as spring bed with constant or linearly variable stiffness. The single stabilizing or destabilizing terms of the formulation are here analyzed and commented, providing practical evaluations to obtain enhancement of response in static and dynamic perspective. A numerical example of a masonry façade with non-linear boundary conditions has been provided highlighting how the choice of stiffness values affects the oscillatory motion and rebound effects. Finally, unit stiffness for masonry/concrete walls and retrofitting techniques, such as steel tie-rods, has been calculated.

Description: The performance of a family of nonlinear generalized single step-single solve (GSSSS) time integration schemes is assessed by comparison of their results in terms of total energy and the agreement with respective results published in the literature. The nonlinear algorithms have been developed by their linear counterparts using a Newton–Raphson iterative procedure to ensure dynamic equilibrium inside each time step. A literature review of the available time integration schemes used for nonlinear problems and the family of linear GSSSS algorithms are presented along with several commonly used time integration algorithms as special cases. Afterwards, the nonlinear schemes are formulated, and outlined in an explicit flowchart, which describes the nonlinear integration procedure in detail. The nonlinear family of algorithms is applied to six benchmark problems involving the dynamic response of SDOF systems with various stiffness and damping properties, as well as to a 3dof structure representing finite element systems containing rigid connections, penalty factors and other such types of constraints. It is shown that the schemes with Continuous Acceleration formulation (such as the HHT-a method) perform in general better than the others, even with a large time step, which leads to reduced computational effort for the estimation of the nonlinear dynamic response with relatively little loss of accuracy.

Description: Seismic design of structures is commonly performed by using design spectra by national technical codes or, in some “advanced” designs, by using design acceleration time-histories given by 1D free-field soil response analyses. These procedures can lead to erroneous evaluations of the “real” inputs, which hit aboveground and underground structures due to complex interactions involving the soil and the structures. Great attention has recently been devoted to separated tunnel–soil interaction analyses and soil-aboveground structure interaction analyses. Analyses involving tunnel–soil–aboveground structures (full-coupled systems) are still very rare. The present paper deals with the dynamic interaction that occurs between a tunnel, the soil and an aboveground building, it also investigates the effects of the tunnel on the response of the soil and/or of the building and vice versa. The study has been performed using full-coupled FEM modelling. A case-history of the Catania (Italy) underground network has been analysed. A cross-section of the underground network in Catania including an aboveground building has been modelled, by studying its behaviour during the expected scenario earthquake ( M S  = 7.0–7.4). The authors have investigated the seismic behaviour of the system in terms of acceleration time-histories, amplification ratios, Fourier amplitude spectra, as well as seismic bending moments and axial forces of the tunnel lining.

Description: This paper is a reappraisal of the study on the single-station sigma for Italian strong-motion stations carried out by Luzi et al. (Bull Seismol Soc Am 104:467–483, 2014 ). A residual analysis considering the time interval 1972–2015 is carried out on two datasets, using 4.0 and 3.5 as magnitude thresholds, and the ground motion prediction equations by Bindi et al. (Bull Earthq Eng 9:1899–1920, 2011 ) as reference model for the calculations of the expected median intensity measures. The magnitude threshold of 3.5 is selected with the aim of obtain the largest number of records for each station and evaluate the influence of low magnitude events on the standard deviation of the residual components. The dataset contains about 8400 waveforms, relative to 522 events, recorded by 600 strong-motion stations, about five times the stations considered in Luzi et al. ( 2014 ). We also discuss elements that can influence the variability at individual station, as the number of records, the presence of analog waveforms and records from multiple source-to-site paths. For each station, the event-corrected single-station standard deviation for an individual site, ϕ ss , s , and the site-term, δS2S s , have been provided. The results of this study can be used as input for the site-specific probabilistic seismic hazard assessment in Italy, removing the ergodic assumption.

Description: The article presents a comparison of different probabilistic methods for ground motion hazard assessments that include site effects. The approaches examined here were selected and refined during the different phases of the S2-Project, which this journal volume is addressed to. Different procedures characterized by different levels of sophistication, from the simpler one based on the use of standard ground motion predictive equations for specific ground types to the more complex one based on the convolution of a site-specific amplification function (and its variability) with the hazard curve for reference rock, are compared and contrasted with the aim of pointing out strengths and weaknesses of each of them. In addition, a fully non-ergodic approach that separates the epistemic contribution (i.e., the epistemic uncertainty affecting the soil properties) from the total variability in site amplification is presented. To fulfill the scope of the work, the study focuses on three test sites in Italy characterized by different geological conditions and seismicity levels: Mirandola and Soncino in the Po Plain (northern Italy) and Peglio in central Italy.

Description: During an earthquake, the presence of tunnels may affect the seismic wave propagation in the involving soil and in turns the response of aboveground structures. At the same time, the vibrations of aboveground structures may create a complex interaction with the tunnel and, consequently, they may modify the dynamic response of the tunnel. Most of the published papers considered only tunnel–soil systems or only soil−aboveground structures; analyses involving tunnel plus soil plus aboveground structures (full-coupled analyses) are still very rare. The present paper deals with a parametric analysis: starting from a real case-history regarding the Catania (Italy) underground network, and in particular a cross-section including an aboveground building, the depth of the tunnel, the position of the aboveground building and the seismic inputs were modified in order to study their effects on the dynamic tunnel–soil–aboveground building interaction. Thirty different recorded accelerograms were adopted. Results are reported in terms of accelerations in the time and frequency domains, as well as in terms of seismic bending moments and axial forces of the tunnel lining.

Description: An important advancement in structural engineering in recent years has been the development of performance-based design (PBD). However, its application to cold-formed steel framed buildings remains largely unexplored. This paper presents the assessment of the bracing capacity of cold-formed steel stud bracing wall panels using a direct-displacement based design (DDBD) approach. The fundamentals of DDBD using equivalent damping, and inelastic displacement response spectra approaches are presented. These wall parameters needed for each approach are evaluated from experimental load–deflection response behaviour under quasi-static cyclic loading. Results obtained from the DDBD approach are compared with results from conventional non-linear time history analyses (NLTHA) to confirm the validity of the adopted approach. It is found that results estimated from DDBD method using inelastic displacement response spectra approach correlated much better with NLTHA results than the equivalent damping method.

Description: The seismic responses of steel buildings with perimeter moment resisting frames (MRF) with welded connections (WC) are estimated and compared to those of similar buildings with semi-rigid post-tensioned connections (PC). The responses are estimated in terms of ductility reduction factors (R µ , ) , ductility demands ( µ G ) and force reduction factors ( R ). Two steel model buildings, which were modeled as complex-3D-MDOF systems, were used in the study. Results indicate that the reduction magnitude of global response parameters is larger than that of local response parameters, contradicting the same reduction implicitly assumed in the static equivalent lateral force procedure, implying that non-conservative design may result. The value of 8 for R , suggested in many codes for ductile steel MRF, and the value of 1 suggested in the well known Newmark and Hall procedure for the ratio of R to µ G , cannot be justified. The reason for this is that SDOF systems were used to model actual structures, where higher mode effects, energy dissipation and structural overstrength weren’t explicitly considered. The codes should be more transparent regarding the magnitude and the components involved in the force reduction factors. The seismic performance of steel buildings with PC may be superior to that of the buildings with WC, since their force reduction factors are larger and their ductility demands smaller, implying that PC buildings could be designed for smaller lateral seismic forces. The conclusions of this paper are for the particular structural systems and models considered. Much more research is needed to reach more general conclusions.

Description: This paper attempts to develop a mathematical model for estimating the seismic response of a cylindrical shaped nuclear reactor building resting in an elastic halfspace considering foundation compliance. Most of the research carried out on this topic has either been carried out by resorting to finite element method (FEM) which makes the computational cost expensive or based on the simplifying assumption of assuming the cylindrical structure as a multi degree lumped mass stick model with soil coupled as boundary springs. In the present paper an analytical model has been developed in which the deformation of the cylindrical body (including its shear deformation characteristics) has been taken into cognizance and then coupling with foundation stiffness a comprehensive solution has been sought based on Galerkin’s weighted residual technique. The results are finally compared with FEM to check the reliability of the same. The results are found to be in good agreement with the detailed finite element analysis.

Description: In this paper maximum response of a single degree of freedom system resting on a flexible base is determined under consistent earthquakes and the results are presented as acceleration spectra including soil–structure interaction (SSI). Flexibility of base is modeled using frequency-dependent springs and dampers. The spring–damper coefficients are calculated for the desired natural mode of vibration of a multi-degree-of-freedom system. Consistency of earthquakes is maintained considering their magnitude, distance, local soil type, and return period. The latter parameter is accounted for by the use of earthquake categories identified by their similar spectral values. Ratio of spectral acceleration modification factors with SSI from this study to those calculated using the ASCE 7-10 procedure are determined for each case. Examination of the resulting curves shows that the mentioned code is conservative/non-conservative in estimation of spectral responses with SSI in certain cases for the lower/higher modes of vibration. The code’s procedure is modified using the developed curves for a conversion factor.

Description: This article presents an overview of the different processes of data recollection and the analysis that took place during and after the emergency caused by the M w 8.8 2010 Maule earthquake in central-south Chile. The article is not an exhaustive recollection of all of the processes and methodologies used; it rather points out some of the critical processes that took place with special emphasis in the earthquake characterization and building data. Although there are strong similarities in all of the different data recollection processes after the earthquake, the evidence shows that a rather disaggregate approach was used by the different stakeholders. Moreover, no common standards were implemented or used, and the resulting granularity and accuracy of the data was not comparable even for similar structures, which sometimes led to inadequate decisions. More centralized efforts were observed in resolving the emergency situations and getting the country back to normal operation, but the reconstruction process took different independent routes depending on several external factors and attitudes of individuals and communities. Several conclusions are presented that are lessons derived from this experience in dealing with a large amount of earthquake data. The most important being the true and immediate necessity of making all critical earthquake information available to anyone who seeks to study such data for a better understanding of the earthquake and its consequences. By looking at the information provided by all these data, we aim to finally improve seismic codes and engineering practice, which are important social goods.

Description: Is Europe-wide operational earthquake forecasting (OEF) possible? We discuss the myriad problems that prevent it today, many of which relate to heterogeneities in earthquake recording, processing, and reporting. We contemplate the difficulty of building models that cross political boundaries, and we consider the prospect of European OEF in light of recent efforts to harmonize long-term seismic hazard assessment among several nations. Emphasizing the Strategies and Tools for Real-time Earthquake Risk Reduction (REAKT) project, we report achievements related to short-term seismicity forecasting in Iceland and Italy that could apply elsewhere in Europe. In Iceland, collaboration fostered by REAKT resulted in a revised earthquake catalog and a prototype OEF system. We report results from an experiment conducted with this prototype; these results suggest ensemble models provide an information gain, updating models more frequently improves their forecast skill, and that OEF is computationally feasible. In Italy, REAKT supported the creation of an ensemble model that now issues weekly hazard forecasts. We present examples of these forecasts, highlighting the problem that OEF often yields low probabilities, which are difficult to interpret and convert into actionable decisions. Motivated by such low hazard probabilities, we highlight Europe’s pioneering efforts in operational earthquake loss forecasting and mention solutions to problems that currently prevent OEF at the European scale.

Description: Based on a pseudo-static approach, finite difference (FDM) numerical analyses have been performed aimed at evaluating the seismic effects on the ultimate bearing capacity of shallow strip foundations. In the specialised literature, such seismic effects are usually divided in two components, namely, a structure inertia and a soil inertia , which can be either considered together, or separately addressed and then superposed. Both of these inertia effects are investigated in this work. The results of a comprehensive numerical study are presented in—and critically compared to—the wide framework of available analytical solutions proposed in the literature in the last 30 years. The good agreement found between the numerical and the analytical approaches is pointed out, thus providing further evidence of the reliability of some available and widespread solutions. The possibility of superposition of the two inertia effects is investigated. It is found that in some cases the soil inertia may play a significant role in the seismic capacity of the system, and that simple one-constant equations can be readily used in foundation design to estimate the reduction in bearing capacity (namely, factors e i , e k ) deriving from the two inertia effects.

Description: The last release of the strong-motion database ITACA (ITalian ACelerometric Archive v 2.1, http://itaca.mi.ingv.it ) includes, to date, about 25,222 three-component accelerometric waveforms generated by 1365 earthquakes with magnitude between 3.0 and 6.9 and recorded by 1210 stations in the time frame 1972–2015. One of the main goals of ITACA is to improve the characterization of the recording sites from the geological and geophysical point of view and to provide seismic classification according to Italian seismic code. To this aim, metadata of recording stations are stored in three main thematic levels (topographic features, geological features and geophysical measurements) useful for a large variety of applications in engineering seismology or earthquake engineering. In particular, 206 recording stations have been characterized by quantitative measurements of velocity profiles, conducted through different techniques (active and/or passive), and the V S,30 values are available in ITACA 2.1. Moreover, 357 horizontal to vertical spectral ratios of Fourier spectra of ambient noise and the value of the fundamental frequency are also accessible. All details about the stations contained in the ITACA database are described in specific reports.

Description: This paper investigated the effects of basin geometry and material property on the response of 2D trapezoidal sediment-filled basin to incident plane SH waves. Ten basin configurations with different geometries were developed, and then their seismic responses to both Ricker wavelets and seismic records were simulated by using an explicit finite difference scheme. The definition of deep/shallow basin, the precondition for the observation of prominent surface waves and the influential area of edge effects of the shallow basin were discussed quantitatively in this study. The followings were concluded: in the common velocity contrast range ( v s 1 / v s 2  〈 10), the fundamental frequency a basin with W / H  〉 3.0 can be estimated approximately by 1D theory. The complexity of peak ground acceleration distribution pattern, the width of the most affected section as well as the amplitude of ground motion in the Edge Region increase with incident frequency. Prominent surface waves can only be observed when the incident wavelength is shorter than the critical wavelength λ c . The interaction between incident wave and basin dynamic property plays a dominant role on the peak ground acceleration amplitude while the interaction between incident wave and geometry plays a more significant role on the peak ground acceleration distribution. For very shallow basin, different areas along the basin width are affected to different extents. Only a limited area close to the basin edge is influenced significantly. It is more feasible to propose spectral aggravation factor for different surface zones respectively than a uniform constant as a tool to calibrate the 1D-based design spectrum so as to take the basin effects into account.

Description: Resonance period is a key parameter in the seismic design of a structure, thus dynamic parameters of buildings in Beirut (Lebanon) were investigated based on ambient vibration method for risk and vulnerability assessment. Lebanon is facing high seismic hazard due to its major faults, combined to a high seismic risk caused by dense urbanization in addition to the lack of a seismic design code implementation. For this study, ambient vibration recordings have been performed on 330 RC buildings, period parameters extracted and statistically analyzed to identify correlations with physical building parameters (height, horizontal dimensions, age) and site characteristics (rock sites or soft sites). The study shows that (1) the building height or number of floors (N) is the primary statistically robust parameter for the estimation of the fundamental period T; (2) the correlation between T and N is linear and site dependent: T ≈ N/23 for rock sites and N/18 for soft sites; (3) the measured damping is inversely proportional to the period: the taller the building the lower is the damping; (4) a significant overestimation of the period exists in current building codes. However part of the large discrepancy with building code recommendations may be due to the very low level of loading.

Description: Following the 1995 Kobe earthquake, many RC bridge columns were demolished due to a residual drift ratio of more than 1.75 % even though they did not collapse. The residual drift ratio is a quantitative index for the performance objective of reparability in the bridge seismic design. Numerical models of the columns are built to study the factors that influence the residual displacement of RC bridge columns. In these models, both column bending and bar pulling out deformation are considered using the fiber column-beam element and zero-length section element, respectively. Then, nonlinear time history analyses are performed. The factors that influence column residual displacement, such as the characteristics of ground motion, the structural responses (the maximum lateral drift ratio and the displacement ductility factor), and the structural characteristics (the aspect ratio and the longitudinal reinforcement ratio) are investigated. It is found that the near-fault ground motion induces a larger residual drift ratio than the far-fault ground motion. The residual drift ratio becomes larger due to the increase of the maximum lateral drift ratio, the displacement ductility factor, and the aspect ratio. Further, a larger longitudinal reinforcement ratio can induce a larger residual drift ratio due to the contribution of the bar pulling out deformation.

Description: The Harmonization of Seismic Hazard Maps in the Western Balkan Countries Project (BSHAP) was funded for 7 years by NATO Science for Peace and Security Program to support the preparation of new seismic hazard maps of the Western Balkan Region. In the framework of BSHAP, the regional free field strong motion network capacity was significantly increased by deployed recorders (Gülerce et al. in Final report of improvements in the Harmonized Seismic Hazard Maps for the Western Balkan Countries (BSHAP-2) Project, NATO SfP-984374. http://wbalkanseismicmaps.org/ , 2015 ) and the BSHAP strong motion database that includes both pre-BSHAP (mostly analogue) and post-BSHAP (all digital) recordings was compiled. The BSHAP strong motion database includes uniformly processed strong motions along with the related earthquake metadata and station information; therefore, it provides a solid base for the ground motion characterization studies in the region. The established database is used for selection of the ground motion prediction equations (GMPEs) to be employed in the probabilistic seismic hazard assessment by comparing the compiled strong ground motions with the predictions of candidate global and Euro-Mediterranean GMPEs in a systematic manner. Details of the selection strategy including the analysis of model predictions for ground motion scaling, data testing to evaluate the model performance, and ranking is provided here along with the GMPE logic tree used in the proposed seismic hazard maps by Kuka et al. (Bull Earthq Eng, under review).

Description: After the seismic events of the 20th and 29th of May 2012 in Emilia (Italy), most of the monumental and historic buildings of the area were severely damaged. In a few structures, partial collapse mechanisms were observed (e.g. façade tilting, out-of-plane overturning of panels…). This paper presents the case-study of the bell tower of the Santa Maria Maggiore cathedral, located in Mirandola (Italy). The dynamic response of the structure was evaluated through operational modal analysis using ambient vibrations, a consolidated non-destructive procedure that estimates the dynamic parameters of the bell-tower. The dynamic tests were carried out in pre-intervention and post-intervention conditions in order to understand the sensitivity of dynamic measurements to safety interventions. Furthermore, a comparative study is made with similar cases of undamaged masonry towers up to the 6th mode. Finally, an investigation on the state of connections and of the building itself is carried out via FE model updating.

Description: This paper presents the calibration procedures of a numerical model based on the results of uniaxial and shear-compression tests on three-leaf stone masonry panels in scale 1:1 and 2:3, both in original and injected conditions. The stone masonry panels were simulated considering a macro-scale approach, where a nonlinear continuum damage model with distinct scalar damage parameters for tension and compression, implemented in the finite element software Cast3 M, was used to simulate the walls behaviour. The main goal of this paper is, first to calibrate, based on the obtained experimental results and using a phenomenological calibration strategy, a single set of parameters that represent a macroscopic constitutive law, by type of masonry, which is able to describe the different experimental tests. Afterwards, a parametric study was performed using the calibrated material laws, with the scope of assessing the influence of vertical pre-compression, slenderness and material strength on failure mechanisms and on different performance parameters such as the maximum load and displacement capacity (drift at ultimate state and drift at maximum load), for each type of masonry condition.

Description: An analysis of the damage observed in 24 reinforced concrete (RC) columns tested under uniaxial and biaxial horizontal loading is presented. The test results show that for biaxial loading conditions specific damage occurs for lower drift demands when compared with the corresponding uniaxial demand (a reduction of 50–75 % was found). The damage distribution observed in each column is also analysed. No significant differences are found in the plastic hinge length for uniaxial and biaxial loading. The drift demands associated with each damage state are compared with reference values proposed in international guidelines. Finally, and based on the philosophy of the Park and Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. The results of the application of these expressions to the experimental results are discussed.

Description: A buried pipe extends over long distances and passes through soils with different properties. In the event of an earthquake, the same pipe experiences a variable ground motion along its length. At bends, geometrically a more complicated problem exists where seismic waves propagating in a certain direction affect pipe before and after bend differently. Studying these different effects is the subject of this paper. Two variants for modeling of pipe, a beam model and a beam-shell hybrid model are examined. The surrounding soil is modeled with the conventional springs in both models. A suitable boundary condition is introduced at the ends of the system to simulate the far field. Effects of angle of incidence in the horizontal and vertical planes, angle of pipe bend, soil type, diameter to thickness ratio, and burial depth ratio on pipe strains at bend are examined thoroughly. It is concluded that extensional strains are highest at bends and these strains increase with the angle of incidence with the vertical axis. The pipe strains attain their peaks when pipe bend is around $135^{\circ }$ and exceed the elastic limit in certain cases especially in stiffer soils, but remain below the rupture limit. Then equations for predicting the seismic response of the buried pipe at bend are developed using the analytical data calculated above and regression analysis. It is shown that these semi-analytical equations predict the response with very good accuracy saving much time and effort.

Description: This paper describes a new method for the evaluation of the static eccentricity $e_{s}$ and the ratio $\Omega _{\uptheta } $ of uncoupled torsional to lateral frequencies in real multi-storey buildings. The above-mentioned parameters greatly affect the lateral-to-torsional coupling of the response of asymmetric systems and thus are of paramount importance in the assessment of the in-plan irregularity of buildings. The proposed method, which is a generalization of that suggested by Calderoni et al. (Earthq Spectra 18(2):219–231, 2002 ), allows the calculation of the static eccentricity $e_{s}$ and the ratio $\Omega _{\uptheta } $ from the structural response to arbitrary distributions of forces and torsional couples. The effectiveness of the method is validated on some regularly and non-regularly asymmetric buildings characterised by different in-plan irregularity. The analyses demonstrate that the results of the method are rigorous in the case of regularly asymmetric systems and only slightly depend upon the heightwise distribution of the forces in the case of non-regularly asymmetric systems. Finally, the values of the static eccentricity $e_{s}$ and the ratio $\Omega _{\uptheta } $ resulting from the proposed method are compared to those obtained by means of the procedure suggested by Makarios and Anastassiadis in (Struct Des Tall Spec Build 7(1):33–55, 1998a ; Struct Des Tall Spec Build 7(1):57–71, 1998b ) .

Description: Adding concrete walls by infilling certain frame bays with reinforced concrete is popular for seismic retrofitting, but is covered by codes only if the connection of the old concrete to the new ensures monolithic behavior. To avoid penalizing the foundation of the new wall with a very high moment resistance, the new concrete should not be thicker than, or surround, the old frame members. A cost-effective connection of these members to a thin new web is proposed, alongside a design procedure and detailing that conform to current codes. Owing to practical difficulties, footings of added walls are often small and weakly connected to the other footings, hence they uplift and rock during the earthquake. The model for uplift of 3D footings consists of two pairs of nonlinear-elastic springs in a cross layout and approximates also moderate nonlinearities in the soil continuum. It is used in nonlinear, static or dynamic, analyses of three buildings with added walls. The analyses of a clean, regular 4-story building show the benefit from uplift to the added walls and a certain adverse effect on some columns but not on beams, as well as the lack of a clear positive effect of tie-beams. The application to a 7-story and a 2-story real building with extreme, yet typical, irregularities in plan and elevation exemplifies the real-life restrictions in the use of added walls and shows their limits for the improvement of seismic performance; certain deficiencies in flexure or shear remain in both and are corrected at very low cost with local fiber reinforced polymer (FRP) jackets without new analysis of the building, as FRPs do not change the member effective stiffness or moment resistance.

Description: Frequency-wavenumber (f-k) spectra of seismic strong-motion array data are useful in estimating back-azimuth and apparent propagation velocity of seismic waves arriving at the array. Such estimates are required to model wave passage effects while studying spatial variability of strong ground motion. Although periodogram-based spectral estimates are commonly used, practical applications based on them encounter limitations, such as, lack of objective criteria for selecting a proper smoothing window and its associated bandwidth, and relatively large variance of the estimated spectral quantities. We present an alternative spectral estimate based on parametric time series modelling approach. The well-known autoregressive (AR) time series model is used in a system-based approach to estimate the spectral matrix of auto- and cross-spectral densities. Such spectral estimates are found to be smoother than the windowed periodogram estimates, and can directly be used in f-k spectral analysis. We present an example application of the proposed technique using strong-motion data recorded by the SMART-1 array in Taiwan during the January 29 1981 $M_{L}$ 6.3 earthquake. Our results, in terms of back azimuth and apparent propagation velocity, are found to be in excellent agreement with those reported in the literature.

Description: In this paper we provide an overview of recent research work that contributes to clarify the effects of non-linear dynamic interaction on the seismic response of soil-foundation-superstructure systems. Such work includes experimental results of seismically loaded structures on shallow foundations, theoretical advancements based on improved macro-element modeling of the soil-foundation system, examples of seismic design of bridge piers considering non-linear soil-foundation interaction effects, and numerical results of incremental non-linear dynamic analyses. The objective of this paper is to support the concept of a controlled share of ductility demand between the superstructure and the foundation as a key ingredient for a rational and integrated approach to seismic design of foundations and structures.

Description: The main goals of this article are to analyze the use of simplified deterministic nonlinear static procedures for assessing the seismic response of buildings and to evaluate the influence that the uncertainties in the mechanical properties of the materials and in the features of the seismic actions have in the uncertainties of the structural response. A reinforced concrete building is used as a guiding case study. In the calculation of the expected spectral displacement, deterministic nonlinear static methods are simple and straightforward. For not severe earthquakes these approaches lead to somewhat conservative but adequate results when compared to more sophisticated procedures involving nonlinear dynamic analyses. Concerning the probabilistic assessment, the strength properties of the materials, concrete and steel, and the seismic action are considered as random variables. The Monte Carlo method is then used to analyze the structural response of the building. The obtained results show that significant uncertainties are expected; uncertainties in the structural response increase with the severity of the seismic actions. The major influence in the randomness of the structural response comes from the randomness of the seismic action. A useful example for selected earthquake scenarios is used to illustrate the applicability of the probabilistic approach for assessing expected damage and risk. An important conclusion of this work is the need of broaching the fragility of the buildings and expected damage assessment issues from a probabilistic perspective.

Description: The application of smooth (plain) bars in reinforced concrete (RC) construction has been abandoned since the 1970s; however, there are many old reinforced concrete buildings in the world whose construction is based on this old style that are now in need of structural seismic rehabilitation according to the requirements of present day seismic rehabilitation codes. The focus of this study concerns the investigation of the hysteretic cyclic response of RC columns with smooth bars. The results of six column specimens having a variety of details for overlapping splices of longitudinal bars while experiencing two different levels of axial loads under cyclic loading reversals are presented. Through analysis of test observations and the obtained experimental results, it is attempted to clarify major aspects of hysteretic response for RC columns with smooth bars, from a seismic assessment point of view. The hysteretic force–drift responses of columns are deeply investigated and a new concept explaining the flag shape form of the hysteretic response is presented. Furthermore, the rocking response of columns is predicted with a new formulation that assumes an internal compression strut inside the column body as a consequence of rocking that originated from high base rotations. Finally, a simple hysteresis rule is proposed which is the result of considering the combination of two springs in parallel to provide the total hysteretic response as the summation of rocking hysteretic and bottom anchor (smooth bar) hysteretic responses.

Description: A series of earthquakes, the highest of magnitude $\text{ M }_\mathrm{w}$ M w 5.9, hit a portion of the Po Valley in Northern Italy, which was only recently classified as seismic. The paper reports the findings and the lessons learnt from a preliminary field survey which was conducted immediately after the second event. As a result of the economic attitude of the affected area, and possibly of the characteristics of the event, an unprecedented number of industrial precast buildings were affected, resulting into most of the casualties as well as in large economic losses. Whereas most of the damaged and collapsed buildings were designed for gravity loads only, evidence of poor behavior of some precast buildings designed according to seismic provisions were discovered. The paper provides a description of the performance of precast buildings, highlighting the deficiencies that led to their poor behavior as well as some preliminary recommendations.

Description: Probabilistic performance assessment requires the development of probability distributions that can predict different performance levels of structures with reasonable accuracy. This study evaluates the performance of a non-seismically designed multi-column bridge bent retrofitted with four different alternatives, and based on their performance under an ensemble of earthquake records it proposes accurate prediction models and distribution fits for different performance criteria as a case study. Here, finite element methods have been implemented where each retrofitting technique has been modeled and numerically validated with the experimental results. Different statistical distributions are employed to represent the variation in the considered performance criteria for the retrofitted bridge bents. The Kolmogorov-Smirnov goodness-of-fit test was carried out to compare different distributions and find the suitable distribution for each performance criteria. An important conclusion drawn here is that the yield displacement of CFRP, steel, and ECC jacketed bridge bents are best described by a gamma distribution. The crushing displacement and crushing base shear of all four retrofitted bent follow a normal and Weibull distribution, respectively. A probabilistic model is developed to approximate the seismic performance of retrofitted bridge bents. These probabilistic models and response functions developed in this study allow for the performance prediction of retrofitted bridge bents.

Description: Base isolation has become a widely applied technique for protecting buildings located in highly seismic areas. Due to the strongly non-linear constitutive behaviour typical of many isolation devices, the seismic response of base-isolated buildings is usually evaluated through non-linear dynamic analysis. In this type of analysis a suitable set of ground motions is needed for representing the earthquake loads and for exciting the structural model. Many methods can be found in the literature for defining the ground motions. When natural accelerograms are used, the methods mainly differ from each other based on the intensity measures used for scaling the records to the defined earthquake intensity level. Investigations have been carried out for evaluating the predictive capability of the intensity measures used in these methods: while many studies focused on ordinary buildings, only a few focused on base-isolated ones. The objective of this paper is to evaluate the most commonly used intensity measures, which are currently available in the literature, with respect to their capability to predict the seismic response of base-isolated buildings. Selected for the investigation are two frame structures characterized by a different number of storeys and base-isolated with systems having different properties. Two sets of accelerograms, consisting of ordinary and pulse-like near-fault records, are used in the analyses and in the evaluation of the intensity measures. Modified versions of existing intensity measures are also proposed, with the intent of improving the correlations between the considered intensity measures and response quantities.

Description: Mechanics-based models are developed for the moment, the curvature and the chord rotation at yielding of circular concrete columns or piers, their secant stiffness to the yield point and the ultimate curvature and flexure-controlled ultimate chord rotation in cyclic loading. The strain criteria for yielding or ultimate are calibrated on the basis of over four hundred test results. Besides the model for the secant-to-yield-point stiffness which is in terms of the yield moment and chord rotation, an empirical one, independent of the vertical reinforcement, is fitted to the data. The ultimate chord rotation is obtained from a plastic hinge model employing a plastic hinge length, the yield and the ultimate curvatures of the end section and the fixed-end rotation due to slippage of bars from their anchorage zone beyond the column length. All models are extended to columns the vertical bars of which are lap-spliced within the plastic hinge and to columns with FRP wrapping and continuous or lap-spliced vertical bars. The comprehensive portfolio of expressions proposed for the deformation properties of circular columns is fully consistent across the various situations of continuous or lap-spliced bars, with or without FRP wrapping, and with models developed by the authors from much larger databases of rectangular columns in similar situations; the aspects specific to circular sections are limited to the mechanics-based section analysis for moment and curvature, a purely empirical coefficient for the secant-to-yield-point stiffness and the empirical plastic hinge length.

Description: This paper addresses the seismic analysis of a deeply embedded non-slender structure hosting the pumping unit of a reservoir. The dynamic response in this type of problems is usually studied under the assumption of a perfectly rigid structure using a sub-structuring procedure (three-step solution) proposed specifically for this hypothesis. Such an approach enables a relatively simple assessment of the importance of some key factors influencing the structural response. In this work, the problem is also solved in a single step using a direct approach in which the structure and surrounding soil are modelled as a coupled system with its actual geometry and flexibility. Results indicate that, quite surprisingly, there are significant differences among prediction using both methods. Furthermore, neglecting the flexibility of the structure leads to a significant underestimation of the spectral accelerations at certain points of the structure.

Description: The relative density can be used as the main indicator to assess the liquefaction resistance of clean sands. As relative density of the sand deposit increases significantly following the initial liquefaction, one should expect that the soil can improve its liquefaction resistance. However, earthquake records indicate that densified sand can be liquefied again (re-liquefied) at smaller cycles by the similar seismic loadings. This work aims to clarify the counterintuitive finding that, after the first liquefaction, the resulting significant increase in relative density (induced by settlements and variation of the water level) do not necessarily imply an increase in the number of loading cycles for re-liquefaction. In this paper, we present a series of experimental results concerning the cyclic liquefaction and the following re-liquefaction of clean sand deposits. The experimental setup is performed by a shaking table, transmitting one-degree of freedom transversal motion to the soil within the 1.5 m high laminar shear box. At four different seismic demands, the input excitation was imposed three times to examine the influence of the initial distributions of the relative density and the consolidation characteristics on the liquefaction potential of the sand. The re-liquefaction cycles of the sand, which previously experienced liquefaction under the same seismic loadings, show that post-liquefaction reconsolidation of the sand deposits affects the re-liquefaction resistance.

Description: In seismic design of extended multi-span bridges the question always arises whether using either natural or artificially generated earthquake records that are identical at all bridge supports is valid or not. It is likely that earthquake ground motion remarkably differs at the various support/pier locations in terms of amplitude, frequency content and arrival time, inducing under certain circumstances significant forces and deformations that would not develop if the assumption of synchronous excitation was adopted. This paper hence illustrates the impact of ground motion spatial variability on the seismic performance and vulnerability of extended continuous box girder bridges in both bridge orthogonal directions (longitudinal and transverse). For illustration purposes, a nine-span bridge with a total length of 430 m is adopted. Non-linear time history analyses are carried out using opensees software. The effects of the spatial variability in the ground motions at the different bridge supports are investigated using a set of 20 artificially simulated seismic ground motions generated using sim software developed in the mid-nineties, considering different degrees of loss in coherency and various soil types (i.e., frequency contents). Results of the non-linear time history analyses performed in an incremental dynamic analysis context are hence manipulated through a probabilistic analysis framework to generate fragility curves associated with various performance levels for the case study bridge. Fragility curves giving the conditional probability of exceeding various performance levels are then integrated with generated hazard curves defining the expected seismic hazard in Egypt. The outcome of this integration process results in values of mean annual frequency of exceeding pre-defined performance levels.

Description: A series of large-scale shaking table tests were performed to investigate the damage mechanisms of a three-arch type subway station structure in a liquefiable soil experiencing strong motions. Methods to measure the displacement included the vision-based displacement test and the fiber Bragg grating test to measure the strain of the galvanized steel wire. Sand boils, waterspouts, ground surface cracks and settlements, and buoyancy movement of the model structure were observed. When the peak excess pore pressure ratios dramatically increased, the Arias intensity also dramatically increased. The peak acceleration of the model soil also almost coincided with liquefaction of the model soil. The seismic responses of the model structure and the soil were shown to be more sensitive to input motions with larger low-frequency components, the phenomenon of high frequency filtering and low frequency amplification effect of the liquefied soil were observed. The peak tensile strain located at the top and bottom of the center pillars was larger than that obtained at the subarch, while the peak tensile strain at the atrium arch was the smallest. The peak strain at the primary and secondary observation sections were remarkably affected by the spatial effect. The results can provide valuable insight into the seismic investigation of these subway structures.

Description: The global ductility parameter \((\mu _{G})\) , commonly used to represent the capacity of a structure to dissipate energy, and its effects, considered through the ductility reduction factor \((R_{\upmu })\) , are studied for buildings with moment resisting steel frames (MRSF) which are modeled as complex multi degree of freedom systems. Results indicate that the \(\mu _{G}\) value of 4, commonly assumed, cannot be justified, a value between 2.5 and 3 is suggested. The ductility reduction factors associated to global response parameters may be quite different than those of local response parameters, showing the limitation of the commonly used equivalent lateral force procedure (ELFP). The ratio \((Q)\) of \(R_{\upmu }\) to \(\mu _{G}\) is larger for the models with spatial MRSF than for the models with perimeter MRSF since their ductility demands are smaller and/or their ductility reduction factors larger. According to the simplified Newmark and Hall procedure, the \(Q\) ratio should be equal to unity for the structural models under consideration. Based on the results of this study, this ratio cannot be justified. The reason for this is that single degree of freedom systems were used to derive the mentioned simplified procedure, where higher mode and energy dissipation effects cannot be explicitly considered. A value of 0.5 is suggested for \(Q\) for steel buildings with perimeter MRSF in the intermediate and long period regions. The findings of this paper are for the particular structural systems and models used in the study. Much more research is needed to reach more general conclusions.

Description: Both the April 6, 2009 L’Aquila (Italy) earthquake, and the 2010–2011 Canterbury (New Zealand) earthquake sequence provided unprecedented opportunity to enhance the understanding on earthquake performance of infrastructure systems, and to analyse still-opened issues affecting the post-earthquake assessment and management of infrastructure. This paper provides a succinct and holistic overview on the physical and functional performances of the gas, water, waste water, road and electric networks (this one to a limited extent for the L’Aquila case-study), following the moment magnitude (M w ) 6.3 L’Aquila earthquake, and two main events of the Canterbury earthquake sequence, namely: the M w 7.1 September 4, 2010 Darfield and the M w 6.2 February 22, 2011 Christchurch earthquakes. A structured format, based on internationally recognised taxonomies and damage descriptors, is introduced to present the assets and to report on the earthquake-induced physical impacts for both above-ground and underground components. Functional impacts, interdependency issues and resilience attributes observed during the emergency management and recovery phases for the same infrastructure systems are furthermore discussed in the paper. It is envisaged that the data and overview on the seismic performance and management of infrastructure systems presented in the paper can be used to test the effectiveness of existing models and to inform the development of new models for seismic risk assessment and resilience analysis. Also, the structured framework presented within this paper can form the basis for defining specific and standardised survey tools for post-earthquake assessment of infrastructure systems.

Description: Model-based feedforward–feedback tracking control has been shown as one of the most effective methods for real-time hybrid simulation (RTHS). This approach assumes that the servo-hydraulic system is a linear time-invariant model. However, the servo-control closed-loop is intrinsically nonlinear and time-variant, particularly when one considers the nonlinear nature of typical experimental components (e.g., magnetorheological dampers). In this paper, an adaptive control scheme applying on a model-based feedforward–feedback controller is proposed to accommodate specimen nonlinearity and improve the tracking performance of the actuator, and thus, the accuracy of RTHS. This adaptive strategy is used to estimate the system parameters for the feedforward controller online during a test. The robust stability of this adaptive controller is provided by introducing Routh’s stability criteria and applying a parameter projection algorithm. The tracking performance of the proposed control scheme is analytically evaluated and experimentally investigated using a broadband displacement command, and the results indicates better tracking performance for the servo-hydraulic system can be attained. Subsequently, RTHS of a nine-story shear building controlled by a full-scale magnetorheological damper is conducted to verify the efficacy of the proposed control method. Experimental results are presented for the semi-actively controlled building subjected to two historical earthquakes. RTHS using the adaptive feedforward–feedback control scheme is demonstrated to be effective for structural performance assessment.

Description: Ground motion produced by low magnitude earthquakes can be used to predict peak values in high seismic risk areas where large earthquakes data are not available. In the present work 20 local earthquakes (M D ∈[−0.3, 2.2]) occurred in the Campi Flegrei caldera during the last decade were analyzed. We followed this strategy: empirical relations were used to calibrate synthetic modeling, accounting for the source features and wave propagation effects. Once the source and path parameters of ground motion simulation were obtained from the reference data set, we extrapolated scenarios for stronger earthquakes for which real data are not available. The procedure is structured in two steps: (1) evaluation of ground motion prediction equation for Campi Flegrei area and assessment of input parameters for the source, path and site effects in order to use the finite fault stochastic approach (EXSIM code); (2) simulation of two moderate-to-large earthquake scenarios for which only historical data or partial information are available (M w 4.2 and M w 5.4). The results show that the investigated area is characterized by high attenuation of peak amplitude and not negligible site effects. The stochastic approach has revealed a good tool to calibrate source, path and site parameters on small earthquakes and to generate large earthquake scenario. The investigated magnitude range represents a lower limit to apply the stochastic method as a calibration tool, due to the small size of involved faults (fault length around 200/300 m).

Description: The 2010–2011 Canterbury earthquakes, which involved widespread damage during the February 2011 event and ongoing aftershocks near the Christchurch Central Business District, left this community with more than $NZD 40 billion in losses (~20 % GDP), demolition of approximately 60 % of multi-storey concrete buildings (3 storeys and up), and closure of the core business district for over 2 years. The aftermath of the earthquake sequence has revealed unique issues and complexities for the owners of commercial and multi-storey residential buildings in relation to unexpected technical, legal, and financial challenges when making decisions regarding the future of their buildings impacted by the earthquakes. The paper presents a framework to understand the factors influencing post-earthquake decisions (repair or demolish) on multi-storey concrete buildings in Christchurch. The study, conducted in 2014, includes in-depth investigations on 15 case-study buildings using 27 semi-structured interviews with various property owners, property managers, insurers, engineers, and government authorities in New Zealand. The interviews revealed insights regarding the multitude of factors influencing post-earthquake decisions and losses. As expected, the level of damage and repairability (cost to repair) generally dictated the course of action. There is strong evidence, however, that other variables have significantly influenced the decision on a number of buildings, such as insurance, business strategies, perception of risks, building regulations (and compliance costs), and government decisions. The decision-making process for each building is complex and unique, not solely driven by structural damage. Furthermore, the findings have put the spotlight on insurance policy wordings and the paradoxical effect of insurance on the recovery of Christchurch, leading to other challenges and issues going forward.

Description: A simple approach is introduced to identify and calibrate analytical models of multi-story buildings from their vibration records. The method is based on the Transfer Matrix formulation of the response, and requires that vibration time histories are known at every floor of the building. Since this is typically not the case, first a methodology is developed to estimate vibration time histories at non-instrumented floors of the building from those recorded at the instrumented floors, based on the assumption that the mode shapes of a multi-story building can be approximated as a linear combination of the mode shapes of a shear beam and a bending beam. Once the vibration time histories are known at every floor, it is shown by using the Transfer Matrix formulation that the top-to-bottom spectral ratio of the records at a particular story is dependent only on the properties of this story and the stories above. In other words, any change in the characteristics of the stories below does not affect the spectral ratio for this story. Therefore, starting from the top story, we can identify frequency of each story (i.e., story stiffness/story mass), or directly story stiffness if the story mass is known. In addition to system identification, the approach also provides a simple tool to calibrate analytical models of multi-story buildings from their vibration records.

Description: The inertial interaction analysis of a structure founded on piles is usually performed assuming the free-field motion as seismic action at the foundation level, thus neglecting the filtering action often exerted by piles. By contrast, the existence of frequency filtering is confirmed through works referring to theoretical and experimental studies, even if this effect is generally neglected in design practice. In this paper the seismic performance of frame buildings, excited by filtered and free-field input motions is evaluated. The results of these analyses, expressed in terms of top displacement and base shear, allow for assessing the importance of the beneficial effect coming from the piles on the inertial response of the superstructure.

Description: A study concerning the evaluation of seismic response of statues exhibited in art museums, and a base-isolated floor strategy for their enhanced protection, are presented in this paper. Attention is particularly focused on statues made of small tensile strength materials, whose behaviour is simulated by a smeared-crack finite element approach. Seismic performance is assessed by referring to four levels specially postulated herein, and namely: (1) Rest conditions; (2) No rocking; (3) Damage control; and (4) Collapse prevention. The response is investigated via incremental dynamic analysis, by progressively increasing the amplitude of the ground motion histories adopted as inputs, and by relating output data to the limit conditions fixed for the above-mentioned performance levels. The assessment procedure is applied to a demonstrative case study, represented by a marble statue to be exhibited in the museum wing situated at the ground level of a medieval castle in Italy, according to an architectural hypothesis of partial rebuilding and reuse of the stronghold. The design solution for the base-isolated floor consists in a system of double-friction pendulum isolators. The finite element model constitutive laws and parameters, the dynamic analyses carried out in fixed-base and base-isolated floor conditions, and the practical implementation of the assumed performance assessment criteria are reported for the statue examined, along with a selection of technical details of the floor design.

Description: The efficiency of strengthening traditionally built three-leaf stone masonry walls with different types of composite reinforced coating has been investigated. Glass fibre grid in single component fibre reinforced mortar and glass fibre fabric in epoxy resin matrix were used as coating materials. Four different coating types have been applied, with coating placed on one or both sides of the walls, anchored or not anchored to the masonry at the corners of the walls. Ten walls have been tested by subjecting them to cyclic shear loading at constant precompression, among them two walls in the original state as the control specimens. Four walls have been first tested up to the occurrence of the first significant damage, strengthened and then re-tested up to collapse, whereas four walls have been strengthened undamaged and tested up to collapse. All walls failed in shear. Significant increase in lateral resistance with regard to control walls was observed in all cases, up to 2.5–4.0-times the resistance of the control walls. The degree of improvement did not depend on the type of coating but on the technology of application. Although the coating increased the rigidity of the walls, displacement and energy dissipation capacities have been also improved.

Description: Results of an extensive ambient vibration surveys carried out by different research teams in the area damaged by May–June 2012 seismic sequence in Emilia Romagna (Northern Italy) are summarized and analysed. In particular, ambient vibrations were acquired by both single station and seismic array configurations. Average horizontal to vertical spectral ratios (HVSR) at single station measurements were considered to evaluate local resonance phenomena. Despite the fact that general trends that can be detected are the effect of the subsoil configuration, H/V spectral ratios show a significant dependence on meteo-climatic conditions: in particular, HVSR amplitudes in the low frequency range (〈0.5 Hz) correlate significantly with the sea wave activity in the Central Mediterranean. Anyway, resonance frequencies estimated from HVSR peaks appear persistent and have been used to estimate the local depth of impedance contrasts responsible for seismic resonance phenomena. To this purpose, average V S values up to any depth \( h(\bar{V}_{S} (h)) \) were assessed in the form of a standard power law constrained by Rayleigh dispersion curves deduced from the seismic arrays, and borehole data. In the whole area (except in the Mirandola area) two significant interfaces have been identified corresponding to two main resonance frequencies around 0.8–0.9 and 0.25–0.3 Hz respectively. The first one is attributed to a seismic impedance contrast located in the depth range 60–110 m. The second one corresponds to a deeper interface, possibly located at several hundreds of meters of depth. As concerns the Mirandola area, a single interface has been identified with depths varying in the range 50–115 m corresponding to resonant frequencies in the range 0.8–1.4 Hz. Finally a tentative geological interpretation of the above resonant interfaces is presented.

Description: In this study, the seismic performance of integral and conventional bridges is compared particularly considering the differences at their abutments. For this purpose, three existing integral bridges with one, two and three spans are selected and then designed as conventional jointed bridges. The structural models of the integral and conventional bridges are then built including nonlinear structural and dynamic soil–bridge interaction effects. Next, nonlinear time history analyses of the bridge models are conducted using a set of ground motions. In the analyses, the ground motions are scaled to peak ground accelerations ranging between 0.2 and 0.8 g to assess the seismic performance of integral bridges in relation to that of conventional bridges at various ground motion intensities and associated performance levels. The analyses results revealed that integral bridges have superior seismic performance compared to conventional bridges in terms of smaller inelastic rotations at piers and piles, deck displacements, pile axial forces, abutment rotations, pier column drifts and bearing displacements for the bridges under consideration.

Description: This paper presents the results of a series of shake-table tests on a half-scale, four-storey building with reinforced concrete and unreinforced masonry walls. Due to the lack of reference tests, the seismic behaviour of such mixed structures is poorly understood. The test unit was subjected to several runs of increasing intensity yielding performance states between minor damage and near collapse. Before the test, the expected peak table accelerations leading to different limit states were estimated using the capacity spectrum method, and the predicted values corresponded rather well to actual sustained accelerations. Next to these analyses, the paper describes the test unit, instrumentation and input motion, and comments on the response of the mixed structure in terms of damage evolution and global response quantities, such as force–displacement response and drift and acceleration profiles. The raw and post-processed data sets are made publically available, and all relevant information with regard to data organisation and post-processing procedure is described in an appendix to this paper. The test serves therefore as a benchmark for the validation of numerical models of such mixed structures. The project aims at providing a foundation for the development of seismic design and assessment methods of mixed structures, which are currently not covered by structural codes, including Eurocode 8.

Description: The choice of modelling strategy and analysis options has a significant influence on the results of the seismic assessment of existing buildings and therefore it is very important to have an idea of the dispersion in the results due to different hypotheses regarding the structural model. This paper concentrates on pushover analysis, considered as the reference method currently adopted by engineers for the seismic assessment of existing masonry buildings, and on the equivalent-frame macro-element approach, assumed to be a satisfactory compromise between computational effort and accuracy in the results. A logic tree approach is used to treat the different considered options, including the definition of the geometry of the equivalent frame, the distribution of loads among the masonry piers and on the horizontal diaphragms, the degree of coupling between orthogonal walls, the definition of the cracked stiffness of structural elements and the modelling of masonry spandrels. By assigning a value of probability to each end branch of the tree, the distribution of the peak ground acceleration corresponding to the selected limit states can be obtained and, from this distribution, a quantitative estimate (in probabilistic terms) of the effect of modelling uncertainties on the seismic response of masonry structures is derived.

Description: The Indian subcontinent has suffered some of the greatest earthquakes in the world. The earthquakes of the late nineteenth and early twentieth centuries triggered a number of early advances in science and engineering related to earthquakes that are discussed here. These include the development of early codes and earthquake-resistant housing after the 1935 Quetta earthquake in Baluchistan, and strengthening techniques implemented after the 1941 Andaman Islands earthquake, discovered by the author in remote islands of India. Activities in the late 1950s to institutionalize earthquake engineering in the country are also discussed. Despite these early developments towards seismic safety, moderate earthquakes in India continue to cause thousands of deaths, indicating the poor seismic resilience of the built environment. The Bhuj earthquake of 2001 highlighted a striking disregard for structural design principles and quality of construction. This earthquake was the first instance of an earthquake causing collapses of modern multi-storey buildings in India, and it triggered unprecedented awareness amongst professionals, academics and the general public. The earthquake led to the further development of the National Information Centre of Earthquake Engineering and the establishment of a comprehensive 4-year National Programme on Earthquake Engineering Education that was carried out by the seven Indian Institutes of Technology and the Indian Institute of Science. Earthquake engineering is a highly context-specific discipline and there are many engineering problems where appropriate solutions need to be found locally. Confined masonry construction is one such building typology that the author has been championing for the subcontinent. Development of the student hostels and staff and faculty housing on the new 400-acre campus of the Indian Institute of Technology Gandhinagar has provided an opportunity to adopt this construction typology on a large scale, and is addressed in the monograph. The vulnerability of the building stock in India is also evident from the occasional news reports of collapses of buildings under construction or during rains (without any earthquake shaking). Given India’s aspirations to be counted as one of the world’s prosperous countries, there is a great urgency to address the safety of our built environment. There is a need: to create a more professional environment for safe construction, including a system for code enforcement and building inspection; for competence-based licensing of civil and structural engineers; for training and education of all stakeholders in the construction chain; to build a research and development culture for seismic safety; to encourage champions of seismic safety; to effectively use windows of opportunity provided by damaging earthquakes; to focus on new construction as opposed to retrofitting existing buildings; and to frame the problem in the broader context of overall building safety rather than the specific context of earthquakes. Sustained long-term efforts are required to address this multi-faceted complex problem of great importance to the future development of India. While the context of this paper is India, many of the observations may be valid and useful for other earthquake-prone countries.

Description: To estimate the demand of structures, investigating the correlation between engineering demand parameters and intensity measures (IMs) is of prime importance in performance-based earthquake engineering. In the present paper, the efficiency and sufficiency of some IMs for evaluating the seismic response of buried steel pipelines are investigated. Six buried pipe models with different diameter to thickness and burial depth to diameter ratios, and different soil properties are subjected to an ensemble of 30 far-field earthquake ground motion records. The records are scaled to several intensity levels and a number of incremental dynamic analyses are performed. The approach used in the analyses is finite element modeling. Pipes are modeled using shell elements while equivalent springs and dashpots are used for modeling the soil. Several ground motion intensity measures are used to investigate their efficiency and sufficiency in assessing the seismic demand and capacity of the buried steel pipelines in terms of engineering demand parameter measured by the peak axial compressive strain at the critical section of the pipe. Using the regression analysis, efficient and sufficient IMs are proposed for two groups of buried pipelines separately. The first one is a group of pipes buried in soils with low stiffness and the second one is those buried in soils with higher stiffness. It is concluded that for the first group of pipes, \(\sqrt {{\text{VSI}}[\upomega_{1} ({\text{PGD}} + {\text{RMS}}_{\text{d}} )]}\) followed by root mean square of displacement (RMS d ) are the optimal IMs based on both efficiency and sufficiency; and for the second group, the only optimal IM is PGD 2 /RMS d .

Description: Some Mediterranean seismic codes consider wide-beam reinforced concrete moment resisting frames (WBF) as horizontal load carrying systems that cannot guarantee high ductility performances. Conversely, Eurocode 8 allows High Ductility Class (DCH) design for such structural systems. Code prescriptions related to WBF are systematically investigated. In particular, lesson learnt for previous earthquakes, historical reasons, and experimental and numerical studies underpinning specific prescriptions on wide beams in worldwide seismic codes are discussed. Local and global ductility of WBF are then analytically investigated through (1) a parametric study on chord rotations of wide beams with respect to that of deep beams, and (2) a spectral-based comparison of WBF with conventional reinforced concrete moment resisting frames (i.e. with deep beams). Results show that the set of prescriptions given by modern seismic codes provides sufficient ductility to WBF designed in DCH. In fact, global capacity of WBF relies more on the lateral stiffness of the frames and on the overstrength of columns rather than on the local ductility of wide beams, which is systematically lower with respect to that of deep beams.

Description: The determination of displacement demands for masonry buildings subjected to seismic action is a key issue in the performance-based assessment and design of such structures. A technique for the definition of single-degree-of-freedom (SDOF) nonlinear systems that approximates the global behaviour of multi-degree-of-freedom (MDOF) 3D structural models has been developed in order to provide useful information on the dependency of displacement demand on different seismic intensity measures. The definition of SDOF system properties is based on the dynamic equivalence of the elastic properties (vibration period and viscous damping) and on the comparability with nonlinear hysteretic behaviour obtained by cyclic pushover analysis on MDOF models. The MDOF systems are based on a nonlinear macroelement model that is able to reproduce the in-plane shear and flexural cyclic behaviour of pier and spandrel elements. For the complete MDOF models an equivalent frame modelling technique was used. The equivalent SDOF system was modelled using a suitable nonlinear spring comprised of two macroelements in parallel. This allows for a simple calibration of the hysteretic response of the SDOF by suitably proportioning the contributions of flexure-dominated and shear-dominated responses. The comparison of results in terms of maximum displacements obtained for the SDOF and MDOF systems demonstrates the feasibility and reliability of the proposed approach. The comparisons between MDOF and equivalent SDOF systems, carried out for several building prototypes, were based on the results of time-history analyses performed with a large database of natural records covering a wide range of magnitude, distance and local soil conditions. The use of unscaled natural accelerograms allowed the displacement demand to be expressed as a function of different ground motion parameters allowing for the study of their relative influence on the displacement demand for masonry structures.

Description: Single-core and to a certain extent multi-core lead-rubber bearings have been extensively used in seismic isolation. Yet their behavior is not well understood and experimentation is required to obtain their mechanical properties. A recently developed and validated theory contributed to the understanding of the effects of heating of the lead core on the characteristic strength and ability to dissipate energy of these bearings. Additional results on the theory of heating of lead-rubber bearings are presented in this paper, including readily useable data on the rise of temperature in the steel shim and end plates of these bearings. The results may be used in the assessment of the validity of the theory of lead core heating in single and multi-core lead-rubber bearings and in recently developed multi-core lead-rubber dampers. Examples are presented (including some experimental data) to illustrate the application of the theory. The utility of the presented theory is to reduce the requirements for physical testing of lead-rubber bearings and dampers.

Description: The assessment of the effectiveness of mass dampers for the Chilean region within a multi-objective decision framework utilizing life-cycle performance criteria is considered in this paper. The implementation of this framework focuses here on the evaluation of the potential as a cost-effective protection device of a recently proposed liquid damper, called tuned liquid damper with floating roof (TLD-FR). The TLD-FR maintains the advantages of traditional tuned liquid dampers (TLDs), i.e. low cost, easy tuning, alternative use of water, while establishing a linear and generally more robust/predictable damper behavior (than TLDs) through the introduction of a floating roof. At the same time it suffers (like all other liquid dampers) from the fact that only a portion of the total mass contributes directly to the vibration suppression, reducing its potential effectiveness when compared to traditional tuned mass dampers. A life-cycle design approach is investigated here for assessing the compromise between these two features, i.e. reduced initial cost but also reduced effectiveness (and therefore higher cost from seismic losses), when evaluating the potential for TLD-FRs for the Chilean region. Leveraging the linear behavior of the TLD-FR a simple parameterization of the equations of motion is established, enabling the formulation of a design framework that beyond TLDs-FR is common for other type of linear mass dampers, something that supports a seamless comparison to them. This framework relies on a probabilistic characterization of the uncertainties impacting the seismic performance. Quantification of this performance through time-history analysis is considered and the seismic hazard is described by a stochastic ground motion model that is calibrated to offer hazard-compatibility with ground motion prediction equations available for Chile. Two different criteria related to life-cycle performance are utilized in the design optimization, in an effort to support a comprehensive comparison between the examined devices. The first one, representing overall direct benefits, is the total life-cycle cost of the system, composed of the upfront device cost and the anticipated seismic losses over the lifetime of the structure. The second criterion, incorporating risk-averse concepts into the decision making, is related to consequences (repair cost) with a specific probability of exceedance over the lifetime of the structure. A multi-objective optimization is established and stochastic simulation is used to estimate all required risk measures. As an illustrative example, the performance of different mass dampers placed on a 21-story building in the Santiago area is examined.

Description: Based on our experience in the project REAKT, we present a methodological framework to evaluate the potential benefits and costs of using earthquake early warning (EEW) and operational earthquake forecasting (OEF) for real-time mitigation of seismic risk at nuclear facilities. We focus on evaluating the reliability, significance and usefulness of the aforementioned real-time risk-mitigation tools and on the communication of real-time earthquake information to end-users. We find that EEW and OEF have significant potential for the reduction of seismic risk at nuclear plants, although much scientific research and testing is still necessary to optimise their operation for these sensitive and highly-regulated facilities. While our test bed was Switzerland, the methodology presented here is of general interest to the community of EEW researchers and end-users and its scope is significantly beyond its specific application within REAKT.

Description: Site effects are one of the most predictable factors of destructive earthquake ground motion but results depend on the type of model chosen. We compare simulations of ground motion for a 3D model of the Mygdonian basin in northern Greece (Euroseistest) using different approximation for this basin. Site effects predicted using simple 1D models at many points inside the basin are compared to site effects predicted using four different 2D cross sections across the basin and with results for a full 3D simulation. Surface topography was neglected but anelastic attenuation was included in the simulations. We show that lateral heterogeneity may increase ground motion amplification by 100 %. Larger amplification is distributed in a wide frequency range, and amplification may occur at frequencies different from the expected resonant frequencies for the soil column. In contrast, on a different cross section, smaller conversion of incident energy into surface waves and larger dispersion leads to similar amplitudes of ground motion for 2D and 1D models. In general, results from 2D simulations are similar to those from a complete 3D model. 2D models may overestimate local surface wave amplitudes, especially when the boundaries of the basin are oblique to the selected cross section. However, the differences between 2D and 3D site effects are small, especially in regard of the difficulties and uncertainties associated to building a reliable 3D model for a large basin.

Description: The nonlinear behaviour of masonry piers loaded in their plane is investigated by parametric numerical simulations. Each pier has a cantilever scheme, is loaded by a constant axial load and is subjected to an increasing horizontal displacement at the top. The macro-modelling approach is used to perform numerical analyses, adopting two different constitutive laws: a total strain crack model and a plastic model. The numerical model is calibrated on a block-masonry type for which experimental tests are available in literature. Parametric numerical simulations are performed by varying the aspect-ratio and the compression level, in order to assess the influence of such parameters on both shear strength and displacement capacity. By comparing numerical results with formulas of international codes, a good agreement for the shear strength is obtained, while significant differences are observed for the displacement capacity, which is influenced by both parameters. The authors propose a simple empirical formula for the displacement capacity, obtained by fitting the numerical results. The expression can be useful in the practical design for considering the influence of aspect-ratio and compression level, currently neglected by building codes.

Description: To date, nonlinear dynamic analysis for seismic engineering predominantly employs the classical Rayleigh damping model and its variations. Though earlier studies have identified issues with the use of this model in nonlinear seismic analysis, it still remains the popular choice for engineers as well as for software providers. In this paper a new approach to modelling damping is initiated by formulating the damping matrix at an elemental level. To this regard, two new elemental level discrete damping models adapted from their global counterparts are proposed for its application in nonlinear dynamic analysis. Implementation schemes for these newly proposed models using Newmark incremental method and revised Newmark total equilibrium method is outlined. The performance of these proposed models, compared to existing models, is illustrated by conducting nonlinear dynamic analyses on a four story RC frame designed to Eurocodes. The incremental dynamic analysis study presented in the paper illustrates the fact that both the proposed models seem to produce more reliable results from an engineering perspective in comparison to the global models. It is also shown that the proposed elemental damping models lead to smaller and more realistic damping moments in the plastic hinges. Furthermore, these models could be easily included in existing software frameworks without adding noticeably to the computational effort. The computation time required for these models is approximately equivalent to the one required when using the tangent Rayleigh damping matrix with constant coefficients.

Description: Several building codes propose methodologies to account for epistemic uncertainties in the seismic assessment of masonry buildings by selecting a knowledge level and reducing material strengths by means of the associated value of the confidence factor. Previous works showed that, in the case of masonry structures, this approach has various limitations, such as the lack of proper consideration of experimental tests performed. This article focuses on the issue of imperfect knowledge on material properties of existing masonry buildings and proposes a probabilistic methodology for the assessment, based on Bayesian updating of mechanical properties. The use of a Bayesian approach allows to update the values of the material properties assumed a priori as knowledge on the building increases, by taking into account all the experimental information gathered during the assessment process. A large number of simulated assessments is carried out and the values of the confidence factors on material properties are defined through the comparison between the obtained results and those of the reference structure, assumed to be perfectly known. These factors are useful in a more general framework for the assessment of masonry buildings accounting for different sources of uncertainty.

Description: Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature.

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

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

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉

Description: 〈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〉