Nonlinear Static and Dynamic Analyses of a Low-Rise Steel Building

Abstract

Nonlinear static and nonlinear dynamic procedures in the Guidelines for the Seismic Rehabilitation of Buildings (FEMA-273 1997) are used to analyze an existing fourstory steel moment frame building previously damaged in the Northridge earthquake. Results from both types of analyses are compared with the objective of exercising and evaluating the FEMA-273 (1997) procedures for low-rise steel moment frames. Introduction The Guidelines for the Seismic Rehabilitation of Buildings (FEMA-273 1997) is the first publication in the U.S. to provide a uniform and comprehensive methodology that allows engineers to rehabilitate buildings with the objective of attaining specific performance characteristics when subjected to earthquakes of varying severity. Building performance objectives are defined in terms of damage states that have been selected to represent conditions that influence post-earthquake decisions to occupy the building. Examples of performance levels as defined in FEMA-273 (1997) include immediate occupancy, life safety, and collapse prevention. Earthquake severity is characterized using earthquake shaking hazard levels that have specified probabilities of exceedance. A structural model of the building to be rehabilitated together with the specified hazard level is used to estimate seismic demands based on one of 4 alternative analysis procedures: linear static, linear dynamic, nonlinear static (pushover analysis), and nonlinear dynamic analyses. The demands obtained from these analyses are compared to acceptance limits that are based upon the chosen performance level. Decisions can then be made regarding the rehabilitation scheme. The purpose of this paper is to exercise and evaluate the nonlinear static procedure (NSP) and nonlinear dynamic procedure (NDP) in FEMA-273 (1997) as applied to low-rise steel frames. Seismic demands computed from the NDP are compared to corresponding values calculated from the NSP. Both sets of demands are then compared to the acceptance criteria in FEMA-273 and conclusions regarding the provisions are drawn. Building Description The building chosen for analysis is a 4-story special moment-resisting steel frame designed using the 1988 UBC and built in 1993. The structure has two E-W 3-bay