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SUMMARYThis paper presents the e ect of isolator and substructure properties as well as the frequency characteristics and intensity of the ground motion on the performance of seismic-isolated bridges (SIBs) and examines some critical design clauses in the AASHTO Guide Speciÿcation for Seismic Isolation Design. For this purpose, a parametric study, involving more than 800 non-linear time history analyses of simpliÿed structural models representative of typical SIBs, is conducted. The results from the parametric study are then used to derive important design recommendations and conclusions that may be used by bridge engineers to arrive to a more sound and economical design of SIBs. It is found that the SIB response is a function of the peak ground acceleration to peak ground velocity ratio of the ground motion. Thus, the choice of the seismic ground motion according to the characteristics of the bridge site is crucial for a correct design of the SIB. It is also found that the characteristic strength of the isolator may be chosen based on the intensity and frequency characteristics of the ground motion. Furthermore, the isolator post-elastic sti ness is found to have a notable e ect on the response of SIBs.

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This paper presents a simple yet efficient physical theory model that can be used to simulate the inelastic cyclic axial force-axial deformation and axial force-transverse deformation relationships of steel braces. The model consists of a brace idealized as a pin ended member with a plastic hinge located at its midlength. Input parameters of the model are based only on the properties of the brace. The model combines analytical formulations based on the nonlinear behavior of the brace with some semiempirical normalized formulas developed on the basis of a study of available experimental data. The model realistically accounts for growth effect and degradation of buckling capacity due to Baushinger effects and residual kink present within the brace and it is broadly applicable to steel braces with various section types and slenderness ratios. It is observed that the analytically obtained axial force versus axial displacement as well as axial force versus transverse displacement hysteresis loops compare reasonably well with the experimental ones.

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Summary In this study, two new site specific statistical equations are proposed to estimate the inelastic displacement ratio, C1 of structures subjected to far fault (FF) and near fault (NF) ground motions. The proposed equations consider the effects of fundamental vibration period of the structure, T, lateral strength ratio, R and frequency content of the design earthquake record represented by the Ap/Vp ratio (or T0 = 2π/Ap/Vp), which is a function of the earthquake magnitude, distance to fault, faulting mechanism and site class. It was observed that the C1 values obtained from the proposed equations are in good agreement with the calculated results. The flare of the plotted C1 vs. T/T0 curves enables the proposed equations to cover nearly all the calculated C1 data range and give satisfactory results. However, the curves obtained using the C1 equations of several codes and those available in the literature do not cover the whole calculated C1 data range and generally give unconservative results (smaller C1 values) especially in the shorter period range. For the longer period range, the predictions of C1 obtained from the proposed equation and the ones available in the literature are in good agreement with the calculated C1 data. Copyright © 2014 John Wiley & Sons, Ltd.