A Study of Nonlinear Time History Analysis vs. Current Codes Analysis Procedure of Comparing Linear Dynamic Demand with Nonlinear Static Capacity for Ordinary Standard Bridge

Abstract

Nonlinear time history analysis is known for simulating a structure behavior under severe earthquake more proper than other methods. However for simplicity, most of the bridges in the category of Ordinary Standard Bridge (OSB) are being analyzed by a combined procedure which consists of a linear ARS analysis for earthquake response (demand) and a static nonlinear pushover for ultimate displacement (capacity) per the guidelines of many transportation agencies worldwide. The demand and capacity are then compared to determine the safety of the bridge. For the single degree of freedom (SDF) system, this procedure has been proven to be an effective method with satisfactory accuracy. For bridges in the category of OSB but with noticeable characteristics of multi-degree of freedom (MDF) system, large discrepancies between deformation patterns from linear analysis and nonlinear pushover are often observed by engineers. So, the accuracy of conclusion from this procedure is questioned. To explore nonlinear dynamic behavior of these bridges and investigate the adequacy of the popular combined linear with nonlinear analysis procedure, a series of bridges within the category of OSB ranging from slight to severe mass and stiffness unbalance was analyzed. The analysis methods used for each bridge include linear and nonlinear time history analysis, linear ARS analysis and nonlinear static pushover. To ensure valid results comparison, a ground acceleration time history is used for both linear and nonlinear time history analysis. Its frequency domain ARS curve is used for ARS analysis. Selected bridges model, ground acceleration and analysis methods, procedures, results, comparison, discussion, conclusions and suggestions are all presented in the paper.