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The February 6, 2023, Kahramanmaraş earthquakes (Mw7.8 and Mw7.6) in Southeast Turkey ruptured a 300 km section of the East Anatolian Fault, resulting in severe ground motions. These two strong earthquakes occurred 9 hours apart and were followed by large-magnitude aftershocks. Strong ground motions from the Kahramanmaraş earthquakes were recorded by more than 280 strong motion stations.

Nine base-isolated hospital buildings located at distances less than 50 km from the ruptured fault were subjected to strong ground shaking. This paper examines five of the nine hospitals for which seismic isolation designs were available to the authors. The ground motions acting on these hospital buildings were recorded by strong motion stations situated in close proximity. Consequently, the February 6 earthquakes have presented a unique opportunity to assess the seismic performance of base isolation systems during severe earthquakes. All five hospitals were equipped with double spherical sliding (friction pendulum) seismic isolation devices.

Subsequently, the authors conducted site visits to the hospitals following the February 6 earthquakes and collected data on maximum and residual response displacements at their isolation levels, as well as on the seismic response of structural and nonstructural components. The maximum response displacements measured at the isolation levels are compared with the maximum displacements calculated by nonlinear response history analysis under the ground motions recorded at the strong motion stations in close proximity to the hospitals.

Electric power is essential in post-earthquake periods for the continuous functionality of disaster management and emergency services. In addition, interruption of electric power can cause significant economic losses due to downtime of critical facilities. Therefore, it is very important to maintain seismic safety of electric power systems and components. There are existing seismic regulations and standards regarding electric power systems, especially in the United States of America (USA) and Europe. A similar regulation has been prepared recently in Türkiye, which is a country in a seismically active region. This study focuses on the current state of practice regarding the seismic assessment of electrical equipment in power stations and implementation of the regulations on seismic qualification of these systems. Among many electrical equipment, circuit breakers have been selected for case study. The seismic assessment of the selected high voltage equipment has been performed according to the new regulation under the seismic hazard specifically defined for Türkiye. The case study experiment presents the new methodology in evaluating and classifying the seismic response of high voltage electrical equipment and provides insight to the expected behaviour of circuit breakers under earthquake induced action.

Torsional status indicators of asymmetrical plan systems are evaluated. The ratio of two modal participation factors in a translational direction (lower to higher mode) is proved as a more accurate indicator than the ratio of translation and rotation dominant modal periods. Seismic responses of low-rise asymmetric-plan frames are then assessed through linear elastic and nonlinear response analysis of representative systems under bi-axial ground motion pairs. The results revealed that those systems that are initially identified as torsionally stiff exhibit a torsionally stiff nonlinear response, whereas those initially categorized as torsionally balanced or flexible evolve to a stiffer torsional performance.

The equivalent linear static procedure suggested in seismic codes for determining the maximum displacements of seismic isolation systems is evaluated comprehensively for friction pendulum isolators with respect to the benchmark nonlinear response history analysis procedure for a set of radii of curvature and coefficients of friction. A large set of selected and scaled near field ground motions recorded on stiff and soft soils are employed in comparative evaluations. It has been observed that equivalent linear static procedure significantly overestimates the maximum isolator displacements for all practical combinations of radius of curvature and friction coefficient. Overestimation is larger for ground motions on soft soils. Alternatively, a practical description of inelastic displacement spectra is introduced where the hazard is defined in terms of the 1-second spectral acceleration accounting for the seismicity and soil class of the site, and friction pendulum isolation systems are characterized by their radius of curvature and nominal friction coefficient. Employing the proposed design spectra in design and production may lead to significant reductions of the isolator sizes. Moreover, realistic estimation of maximum isolator displacements also leads to realistic estimation of isolator stiffness, as well as the internal design forces of both the isolation system and the superstructure through response spectrum analysis under design spectrum.

The focus of this study is estimating inelastic deformations of building frames by conducting response spectrum analysis. Damping spectra (R-mu-xi-Tspectra) are derived first for SDOF systems defined with their initial period or initial stiffness, in order to attain equal maximum displacements of the companion inelastic systems. Mean spectral relations and their standard deviations are calculated for 566 horizontal pairs of near-fault ground motions. They are further classified with respect to ductility reduction factorR(mu)as well as the earthquake magnitude and soil type, which are found to have notable influence on the effect of damping in reducing maximum displacement. Optimal damping scaling factors are then calculated for converting the standard 5% damped linear elastic spectra to inelastic spectra. Finally, maximum deformations of MDOF building frames are estimated by using the optimal spectral factors through mode superposition analysis. The results are compared with the results obtained from nonlinear response history analysis under different sets of strong ground motions. Mean inelastic deformations are predicted with reasonable accuracy with the proposed procedure. Hence, damping spectra furnishing optimal damping ratios are suggested as a practical tool for assessing the seismic performance of newly designed, code conforming structures.

An analytical procedure is developed for predicting the ductility demands in simple asymmetric-plan structures under earthquake ground motions. The procedure governs regular structures dominated by the lower vibration modes where inelastic response occurs only at the bases of first story columns and at the beam ends, in conformance with the capacity design principles. Torsional ductility spectra are generated for expressing the maximum ductility response of torsionally coupled, generic, single-story, 2-degree-of-freedom inelastic parametric systems. Five parameters characterize the parametric systems: first mode period, uncoupled frequency ratio, stiffness eccentricity, stiff-to-flexible edge strength ratio, and ductility reduction factor. A surrogate modeling approach is developed for converting the properties of the actual systems to those of the parametric system. Mean maximum ductilities of torsionally stiff, equally stiff, and torsionally flexible systems are calculated under a set of design spectrum compatible strong motions for the possible combinations of characteristic parameters. The results obtained from case studies revealed reasonable accuracy of the estimations. The results have indicated that the flexible side frames of torsionally stiff and equally stiff code conforming designs are mainly responsible for providing the intended ductility and energy dissipation capacity whereas the stiff side frames play a secondary role, particularly when the stiff edge is significantly stronger than the flexible edge. However, ductility demands in torsionally flexible systems are significantly larger at both sides compared with torsionally stiff systems.

Uneven distribution of seismic demand in asymmetric-plan structures is a critical concern in earthquake-resistant design. Contemporary seismic design strategies that are based on linear elastic response, single load reduction factor, and uniform ductility demand throughout an asymmetric system generally lead to unsatisfactory performance in terms of realized ductilities and nonuniform damage distribution due to strong torsional coupling associated with asymmetric-plan systems. In many cases, actual nonlinear behavior of the structure displays significant deviation from what is estimated by a linear elastic, force-based seismic design approach. This study investigates the prediction of seismic demand distribution among structural members of a single-story, torsionally stiff asymmetric-plan system. The focus is on the effect of inherent unbalanced overstrength, resulting from current force-based design practices, on the seismic response of code-designed single-story asymmetric structures. The results obtained are utilized to compile unsymmetrical response spectra and uniform ductility spectra, which are proposed as assessment and preliminary design tools for estimating the seismic performance of multistory asymmetric structures. A simple design strategy is further suggested for improving the inelastic torsional performance of asymmetric systems. Providing additional strength to stiff edge members over their nominal design strength demands leads to a more balanced ductility distribution. Finally, seismic responses of several asymmetric case study structures designed with the aid of the proposed strategy are assessed for validating their improved performance.

The main purpose of this study is to develop a reliable model for predicting the input energy spectra of near-fault ground motions for linear elastic and inelastic systems, and to evaluate the effect of damping and lateral strength on energy dissipation demands. An attenuation model has been developed through one-stage nonlinear regression analysis. Comparative results revealed that near-fault ground motions have significantly larger energy dissipation demands, which are very sensitive to earthquake magnitude and soil type. The effect of damping on elastic and inelastic near-fault input energy spectra is insignificant. Near-fault input energy spectra for inelastic systems is dependent on lateral strength ratio R for short period systems, however, there is almost no dependency on lateral strength for intermediate and long period systems, recalling an equal energy rule. This is a significant advantage for an energy-based design approach.

Recent improvements in performance-based earthquake engineering require realistic description of seismic demands and accurate estimation of supplied capacities in terms of both forces and deformations. Energy based approaches have a significant advantage in performance assessment because excitation and response durations, accordingly energy absorption and dissipation characteristics, are directly considered whereas force and displacement-based procedures are based only on the maximum response parameters. Energy-based procedures mainly consist of the prediction of earthquake input energy imposed on a structural system during an earthquake and energy dissipation performance of the structure.

The presented study focuses on the prediction of earthquake input energy. A large number of strong-ground motions have been collected from the Next Generation Attenuation (NGA) project database, and parametric studies have been conducted for considering the effects of soil type, epicentral distance, moment magnitude, and the fault type on input energy. Then prediction equations for input energy spectra, which are expressed in terms of the equivalent velocity (V-eq) spectra, are derived in terms of these parameters. Moreover, a scaling operation has been developed based on consistent relations between pseudo velocity (PSV) and input energy spectra. When acceleration and accordingly velocity spectrum is available for a site from probabilistic seismic hazard analysis, it is possible to estimate the input energy spectrum by applying velocity scaling. Both of these approaches are found successful in predicting the Veq spectrum at a site, either from attenuation relations for the considered earthquake source or from the results of probabilistic seismic hazard analysis conducted for the site.

A practical implementation of generalized multimodal pushover analysis is presented in this study, where the number of pushovers is reduced significantly in view of the number of modes contributing to seismic response. It has been demonstrated in two case studies that the reduced procedure for generalized pushover analysis is equally successful in estimating the maximum member deformations and forces under a ground excitation with reference to nonlinear response history analysis. It is further shown that the results obtained by using the mean spectrum of a set of ground motions are almost identical to the mean of the results obtained from separate generalized pushover analyses. These results are also very close to the mean results of the nonlinear response history analyses, hence motivating the implementation of generalized pushover analysis with design spectrum.

A generalized multi-mode pushover analysis procedure was developed for estimating the maximum inelastic seismic response of symmetrical plan structures under earthquake ground excitations. Pushover analyses are conducted with story-specific generalized force vectors in this procedure, with contributions from all effective modes. Generalized pushover analysis procedure is extended to three-dimensional torsionally coupled systems in the presented study. Generalized force distributions are expressed as the combination of modal forces to simulate the instantaneous force distribution acting on the system when the interstory drift at a story reaches its maximum value during seismic response. Modal contributions to the generalized force vectors are calculated by a modal scaling rule, which is based on the complete quadratic combination. Generalized forces are applied to the mass centers of each story incrementally for producing nonlinear static response. Maximum response quantities are obtained when the individual frames attain their own target interstory drift values in each story. The developed procedure is tested on an eight-story frame under 15 ground motions and assessed by comparing the results obtained from nonlinear time history analysis. The method is successful in predicting the torsionally coupled inelastic response of frames responding to large interstory drift demands. Copyright (c) 2014 John Wiley & Sons, Ltd.