ALBERT

Description: Stochastic ground motion models can facilitate a versatile description of earthquake acceleration time-histories by modulating a white-noise sequence through functions that address spectral and temporal properties of the excitation. This is established by relating the parameters of these functions to earthquake and site characteristics through appropriate predictive relationships. This study focuses on the selection of these predictive relationships to establish direct compatibility to the mean predictions of ground motion prediction equations (GMPEs). A record-based ground motion model is selected as a stochastic ground motion model, and its match to both elastic and inelastic GMPEs is examined. The novel contribution of the present work is that it develops a computationally efficient approach for providing ground motions that can match any chosen GMPE for any desired set of seismicity characteristics or structural periods. Foundation of the methodology is the development of a metamodel to approximate the median predictions of the ground motion model. This is established by selecting a wide range for the parameters of the model, generating ground motions for each of them, and then calculating the median (over different white-noise sequences) spectral acceleration for different structural periods. Based on this database, a Kriging metamodel is developed to provide an efficient approximation of the predictions of the ground motion model. This metamodel is subsequently used to efficiently select the predictive relationships that optimize the match to the chosen GMPE. The numerical accuracy of the metamodel predictions is also explicitly incorporated in this optimization. © 2016 John Wiley & Sons, Ltd.

Description: Summary: An effective way to study the complex seismic soil-structure interaction phenomena is to investigate the response of physical scaled models in 1-g or n-g laboratory devices. The outcomes of an extensive experimental campaign carried out on scaled models by means of the shaking table of the Bristol Laboratory for Advanced Dynamics Engineering, University of Bristol, UK, are discussed in the present paper. The experimental model comprises an oscillator connected to a single or a group of piles embedded in a bi-layer deposit. Different pile head conditions, that is free head and fixed head, several dynamic properties of the structure, including different masses at the top of the single degree of freedom system, excited by various input motions, e.g. white noise, sinedwells and natural earthquake strong motions recorded in Italy, have been tested. In the present work, the modal dynamic response of the soil-pile-structure system is assessed in terms of period elongation and system damping ratio. Furthermore, the effects of oscillator mass and pile head conditions on soil-pile response have been highlighted, when the harmonic input motions are considered. © 2016 John Wiley & Sons, Ltd.

Description: Second-generation performance-based earthquake engineering (PBEE-2) requires a library of component fragility functions to estimate probabilistic damage to a wide variety of building components. The present work draws on a large body of (mostly) post-earthquake reconnaissance and (some) post-earthquake survey observations of traction elevators to create fragility functions useful in PBEE-2. Two surveys provide detailed observations of 115 representative elevators at 12 hospitals shaken in the 1989 Loma Prieta and 1994 Northridge earthquakes and selected without regard to or foreknowledge of damage. Of these, 55 failed and 60 did not. Approximately half were installed after an important code change of 1972, so one can distinguish the performance of pre-1973 and post-1973 elevator construction. They experienced a range of strong motion: 22 with peak ground acceleration (PGA)〈0.25g, 93 with 0.25g〈PGA〈0.85g. The hospitals had elevator failure rates as low as 0% and as high as 100%. A third survey describes damage qualitatively for six sites with PGA≤0.25 and per-site failure rates of 0% to perhaps 30%. Fragility functions are offered where the damage state is the loss of functionality of the elevator. The elevators in these surveys exhibit a median capacity of PGA≈0.35g with a logarithmic standard deviation of 0.40. Capacity is modestly sensitive to whether the elevator was installed before or after 1973. Using building-specific intensity measures such as Sa(T1) does not improve the fragility functions. © 2016 John Wiley & Sons, Ltd.

Description: A comprehensive framework for potential failure modes (PFM) identification and quantification of concrete dams subjected to seismic excitation is presented. A quantifiable indicator of PFM is presented in the context of both linear and nonlinear analyses. As an illustrative example, a thin arch dam subjected to a set of ground motions at different seismic intensity levels is investigated and corresponding PFM quantified. An outcome of this analysis is the probabilistic-based correlation between linear and nonlinear analyses and identification of the optimal intensity measure parameter. This study, is an adaptation and extension of well-accepted procedures defined by the performance-based earthquake engineering paradigm in buildings. © 2016 John Wiley & Sons, Ltd.

Description: The assessment of earthquake loss often requires the definition of a relation between a measure of damage and a quantity of loss, usually achieved through the employment of a damage-to-loss model. These models are frequently characterized by a large variability, which inevitably increases the uncertainty in the vulnerability assessment and earthquake loss estimation. This study provides an insight on the development of damage-to-loss functions for moment-frame reinforced concrete buildings through an analytical methodology. Tri-dimensional finite element models of existing reinforced concrete buildings were subjected to a number of ground motion records compatible with the seismicity in the region of interest, through nonlinear dynamic analysis. These results were used to assess, for a number of damage states, the probability distribution of loss ratio, taking into consideration member damage and different repair techniques, as well as to derive sets of fragility functions. Then, a vulnerability model (in terms of the ratio of cost of repair to cost of replacement, conditional on the level of ground shaking intensity) was derived and compared with the vulnerability functions obtained through the combination of various damage-to-loss models with the set of fragility functions developed herein. In order to provide realistic estimates of economic losses due to seismic action, a comprehensive study on repair costs using current Portuguese market values was also carried out. The results of this study highlight important issues in the derivation of vulnerability functions, which are a fundamental component for an adequate seismic risk assessment. © 2016 John Wiley & Sons, Ltd.

Description: In this study, the coupled horizontal-vertical behavior of elastomeric bearings subjected to dynamic loading is studied in detail. Under extreme dynamic loading, elastomeric bearings exhibit unstable behavior and an instantaneous loss of horizontal stiffness that is recoverable. Building on an earlier study where the authors developed an analytical model for the horizontal behavior of bearings under dynamic loads, in this study, a new analytical model for the coupled horizontal-vertical behavior of the bearings is developed. The coupled behavior of the bearing is first studied for quasi-static loading, and later, the behavior of the bearings under dynamic loading is studied. A clear distinction is made between different types of deformation the bearing undergoes in the vertical direction. Based on experimental results, it is observed that the behavior of the bearings under dynamic loading differs markedly from that observed under static loading. A new analytical model is proposed that can account for the coupled horizontal-vertical behavior of the bearings under dynamic loading. The proposed analytical model for predicting the post-stability vertical behavior of the bearings is verified using experimental results. The model proposed is found to successfully predict the coupled horizontal-vertical behavior of elastomeric bearings. © 2016 John Wiley & Sons, Ltd.

Description: Sustainability and resilience are issues that are recognized worldwide, and increased attention should be placed on strategies to design and maintain infrastructure systems that are hazard resilient, damage tolerant, and sustainable. In this paper, a methodology to evaluate the seismic sustainability and resilience of both conventional and base-isolated steel buildings is presented. Furthermore, the proposed approach is used to explore the difference between the performance associated with these buildings by considering the three pillars of sustainability: economic, social, and environmental. Sustainability and resilience are both considered to cover a comprehensive performance-based assessment content. The uncertainties associated with performance and consequence evaluation of structural and non-structural components are incorporated within the assessment process. The proposed performance-based assessment approach is illustrated on conventional and base-isolated steel buildings under given seismic scenarios. © 2016 John Wiley & Sons, Ltd.