Analysis of Mid-Rise Steel Frame Damaged in Northridge Earthquake

Abstract

This paper presents the findings from a computational investigation performed on the Borax corporate headquarters building, a four-story steel frame structure in which 75% of the steel moment-resisting connections suffered brittle fractures during the 1994 Northridge earthquake. A companion paper provides detailed documentation of the forensic investigation and repair design performed immediately following the earthquake on this structure, which was less than one year old when the earthquake struck. This paper describes a series of preliminary analyses conducted shortly after the forensic investigation and repair were completed. The main objectives were to investigate the behavior of the structure during the earthquake, and to determine whether different levels of established, advanced analysis techniques could estimate the distribution and extent of the damage. The results showed that a three-dimensional nonlinear dynamic analysis using a site-specific accelerogram provides strong correlation with the observed damage, while elastic static and dynamic analyses, two-dimensional nonlinear static and dynamic analyses, and three-dimensional nonlinear static analyses show less correlation. In addition, the results indicate that substantial redistribution of forces may have occurred, and that force distribution most likely had a noticeable effect on the pattern of failures observed in the structure.