Seismic assessment of existing tall buildings: A case study of a 35-story steel building with pre-Northridge connection

Abstract

The Tall Buildings Initiative (TBI) program of Pacific Earthquake Engineering Research Center has been expanded to consider the seismic performance of existing tall buildings. This paper selects a 35-story steel moment resisting frame (SMRF), designed in 1968 with construction details representative of that period, for detailed seismic evaluation in the framework of Performance Based Earthquake Engineering (PBEE). A three-dimensional numerical model capturing the mechanical properties of the most critical structural elements was generated using the program: Open System for Earthquake Engineering Simulation (OpenSees). Systematic nonlinear response history analysis (NRHA) under two basic safety earthquake (BSE) hazard levels for existing buildings were performed following ASCE 41-13 guideline. Probabilistic checks on the confidence levels of the building to achieve collapse prevention (CP) and immediate occupancy (IO) at different hazard levels were conducted based on FEMA 351. In addition, damage and loss analysis was carried out using FEMA P-58 PBEE methodology. Analysis results following different procedures all predicted that the case-study building failed to meet the recommended performance objectives and had a variety of seismic vulnerabilities, and possible retrofits were needed.