Methods for Inelastic Analysis of Bridges

Abstract

The chapter presents in a uniform way the available inelastic analysis methods for the seismic assessment and design of bridges. Since inelastic response-history analysis has long been used for bridges without substantial changes or developments during the last decade, it is presented in a rather brief and concise manner, leaving aside details of the numerical integration of the equations of motion that can be easily found in structural dynamics textbooks. On the contrary, inelastic static (pushover) methods, which have been the focus of extensive research in the recent years, particularly in the direction of extending them to structures with significant higher mode effects (a typical example being the transverse direction of many bridge types), occupy the largest part of the chapter. The methods described do not encompass all variations of pushover analysis techniques that deal with approximate ways for treating higher mode effects; instead, only those methods that have been specifically applied (after proper tailoring) to bridges have been selected. The different methods are presented not in a strict chronological order, but by classifying them into ‘single-mode’ and ‘multi-mode’ pushover analysis procedures. In the first category the now well-known N2 method is described in sufficient length as a typical representative. Within the ‘multi-mode’ pushover category a distinction is made between procedures involving a series of individual-independent modal pushover analyses (among which the modal pushover analysis technique adapted to the needs of bridges is presented in detail) multi-mode procedures based on adaptive incremental implementation of response spectrum analysis for simultaneous modal pushover analyses (the IRSA method is described in detail), and multi-mode procedures based on single-run pushover analysis with modal-combined adaptive seismic load or displacement patterns (the ‘Adaptive Capacity Spectrum Method’ is presented as the most recent version of this approach) For all major approaches to pushover analysis, an effort is made to describe them in such detail that would permit their implementation by the reader, provided, of course, that he/she has the appropriate analytical tools (cf. Ch. 2) and the expertise to use them. Practical application is also facilitated considerably by the information provided in the next chapter.