Structural health monitoring of a 32‐storey steel‐frame building using 50 years of seismic monitoring data

Abstract

AbstractThe case study, Los Angeles 32‐storey residential building, has an exceptionally long seismic observation history, spanning 50 years (1971‐2020), during which it has experienced many earthquakes, some causing extensive damage in the metropolitan area. Records of 13 earthquakes are analyzed, including San Fernando of 1971, to find out if permanent loss of stiffness occurred in the structure since 1971 and to describe statistically its nonlinear elastic behavior, not related to damage. It is a rare example of an instrumented pre‐San Fernando earthquake steel‐frame building, constructed with some on‐site welded column‐beam connections, type of construction that exhibited weaknesses after the Northridge, 1994 earthquake. The identification method consists of fitting equivalent uniform and four‐layer Timoshenko beams models by waveform inversion of bandpass filtered impulse responses, which results in piecewise constant profiles of shear wave velocity (the damage sensitive parameter) and the elastic moduli ratio, reflecting the distribution of structural stiffness along the height. The nonlinear elastic behavior derived from the smaller amplitude data constitutes strain‐dependent baseline for future structural health monitoring of this building. This behavior reveals more prominent strain dependency in the longitudinal direction and stronger variation with strain toward the base of the structure.