Seismic Response of High Rise Steel Buildings Including Second-Order Effects

Rafaa M. Abbas; Anas N. Hassoni

Rafaa M. Abbas Lecturere, Civil Engineering Department College of engineering-University of Baghdad
Anas N. Hassoni M. Sc., Civil Engineering Department College of engineering-University of Baghdad

Keywords: High rise buildings, P-delta analysis, Finite element method, Seismic analysis, Story drift

Abstract

The objective of this research was to study the static and dynamic response of high rise steel buildings due to earthquake excitation considering second-order effects. Different analysis procedures were considered for response analysis including linear and nonlinear procedures. The “amplified first-order” analysis was investigated with the “second-order” analysis, which includes geometric nonlinearity and P-Delta effects. Second-order analysis with linear and nonlinear time history analysis including P-Delta effects was accounted for in this study. Different composite steel building models with different heights up to 50 story and different bracing configurations were analyzed. Finite element approach by using ETABS software was used to conduct this study.

The study revealed that the amplified first-order analysis results compare well with second-order analysis without P-Delta effect for buildings up to 30 stories, for taller buildings, generally, the amplified first-order analysis results for building displacements and story drifts were about 20% greater. Nonlinear second-order analysis with P-Delta effect showed that building displacements and story drifts were increased as the number of the building stories increased and that P-Delta effects were obvious and more significant for 20 story buildings or taller. For time-domain seismic analysis, nonlinear time-history analysis with P-Delta effects yield higher values for building lateral displacements and story drifts when compared with linear and nonlinear time-history analysis without P-Delta effect especially for buildings taller than 20 stories. Generally, including P-Delta effects in the nonlinear time-history analysis found to increase maximum building displacements by 10% and 8% as an average values for forty and fifty story buildings, respectively.