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The design practice of Box-Girder Seat-Type (BGST) bridges in the Western U.S. is continuously evolving based on the results of advanced modeling and analysis techniques. This is mainly to help engineers and researchers to better understand the behavior of BGST bridges during seismic excitations. Within this backdrop, this study fills the gaps in the current knowledge of assessing the combined effect of strong motion duration and spectral shape on the response of bridges using a comprehensive set of numerical simulations and statistical analyses. Three-dimensional finite element models of two real BGST bridges are analyzed using a large set of ground motions obtained from crustal sources and subduction sources. By means of Step-wise regression – and other statistical procedures – the sensitivity of bridge response parameters to various ground motion parameters including Arias Intensity (Ia), RotD50 spectral acceleration at the bridge's first natural period (Sa(T1)), Significant Duration (D5-95), mid-frequency (f), the derivative of the mid-frequency (f’) and time at 30% of cumulated Arias Intensity (tmid) are evaluated. Results indicate that in the case of ground motions arising from shallow crustal sources, Ia and Sa(T1) are the best predictors of the bridge response, and strong motion duration (D5-95) has no statistically meaningful impact on the response of bridges. However, it is observed that the D5-95 of the ground motions ascending from the subduction sources highly affects the bridge response; utilizing D5-95 alongside Sa(T1), or Ia, can significantly increase the accuracy of bridge response estimates. Hence, it is concluded that D5-95 is not an important ground motion intensity measure for ground motion selection for bridges located in areas with crustal earthquakes. In contrast, D5-95 is important in subduction zone ground motions and must be given proper consideration in the design and analysis of BGST bridges.

This paper summarizes the author’s efforts in validation of ground motion simulations during the past few years. In fact, the Southern California Earthquake Center (SCEC) has established a Technical Activity Group (TAG) focused on Ground Motion Simulation Validation (GMSV) in order to develop and implement testing/rating methodologies via collaboration between ground motion modelers and engineering users. Within the GSMV TAG, a significant bulk of research has been produced in the Performance-Based Earthquake Engineering Laboratory (PBEE-Lab) at the University of California, Irvine (UCI) to validate simulated ground motions for past earthquakes using intensity measures and several engineering demand metrics, i.e., elastic and inelastic response spectra, generalized interstory drift and floor accelerations spectra, buildings and bridge peak responses. Here, we summarize the main results and findings of this ongoing study. In particular, the aim is to address, on a statistical basis, whether simulated GMs for four historical earthquakes (i.e., Imperial Valley, Loma Prieta, Landers and Northridge) are biased in terms of Engineering Demand Parameter (EDP) of various structural systems in comparison with real records. We also investigate the dispersion (i.e., intra-event variability) and the sources of possible differences in the seismic response to recorded and simulated GMs. The results of this study are directly relevant to the engineering community establishing validated reference sets of synthetically generated broadband GM, although they are also providing feedback for seismologists who generate simulated GMs for engineering applications.

This paper summarizes the research findings on identifying an appropriate time step (i.e., sampling frequency) for ground motion acceleration time-history in order to maximize computational efficiency and ensure accurate estimation of structural system¡¯s displacement response. With increases in number of degrees of freedom of structural systems, an issue commonly encountered in tall structures, the nonlinear analysis using ground motions with small sampling time becomes quite time consuming. This study proposes a viable method to reduce the analysis time by downsampling ground motion data. Downsampling is achieved by increasing the ground motion¡¯s time step which in turn reduces the overall number of data points. In this method a structure¡¯s Frequency Response Function is used to judge the appropriate time step according to the characteristics of a given ground motion and structural system. Filtering and downsampling techniques are applied to the original ground motion to generate a downsampled ground motion with the goal of obtaining a highly efficient time history analysis without significant error. This paper shows a practical method and delivers the associated tools for proper downsampling of ground motion¡¯s acceleration time-history to be used in response history analysis. The method is not only practical, but also capable of controlling errors in estimates of response. Results of the proposed method are judged in terms of a goodness of fit test, comparing observed responses to the downsampled ground motions with similar estimates using original ground motions for typical SDOF and MDOF structural systems.

This paper is aimed at quantifying the difference between estimates of seismic response of bridges obtained from nonlinear response history analysis and practice-oriented methods (e.g., elastic modal analysis). In particular, this study investigates the effect of the ground motion incidence angle on the structural response of bridges. A 2D SDOF system was preliminarily used to obtain a simplified model of a bridge column. The structure was modeled with two orthogonal elastic perfectly plastic springs, tuned to obtain a target fundamental period in each direction. Nine combinations of fundamental periods were considered, and three sets of 40 bi-directional ground motions each were applied to the structure. Elastic and inelastic analyses were performed using three levels of inelastic behavior, and statistical analyses were conducted to understand the influence of the incidence angle on the ductility demand. The results show a clear dependence of the ductility demand on the incidence angle, with different behaviors between structures with equal fundamental periods in the principal directions and structures with different periods. The 2D SDOF results were later compared with the response of a real bridge column, and ultimately with a bridge model. Corrective adjustment factors were obtained to transform the results of the current approach to their correct value, analyzing also their dependence on the hazard level of reference, on the structural properties, and on the bridge type.