NONLINEAR STATIC AND INCREMENTAL DYNAMIC ANALYSES FOR SEISMIC DOWN-AISLE BEHAVIOR OF RACK STRUCTURES

A numerical campaign comparing the seismic behavior of cold-formed steel rack structures using both Nonlinear Static Analysis (NSA) and Incremental Dynamic Analyses (IDA) is presented. A total of 140 progressively scaled natural ground-motion records, along with 2 different forces distribution for NSA, were applied to a case study model build considering geometrical nonlinearity (P-Delta effects) and using proper elements to reproduce the pinching of beam-to-column joints in case of hogging and sagging bending moment. Data obtained from IDA were statistically processed and compared with the ones from NSA in terms of seismic vulnerability, specifically in terms of displacement demand and capacity, collapse spectral acceleration and proposing an appropriate damage index capable of tracking the state of the system as the spectral acceleration increase. Results show that NSA underestimates the displacement demand of the system and overestimates the collapse intensity measure (capacity spectral acceleration), thus not always being on the safe side.