Numerical Simulation of a Reduced-Scale 4-Story Steel Moment-Resisting Frame Tested to Collapse

Numerical simulation was conducted to examine how closely recorded response of a shake-table test could be reproduced. The shake-table specimen was a 40%-scale, 4-story steel moment-resisting frame subjected to unidirectional excitation of JMA Kobe-NS record scaled from 10 to 100%. After repeated shaking, the specimen developed substantial yielding and fracture at multiple beam ends, and the first two stories developed story drift ratio exceeding 0.1 rad. A two-dimensional model of the specimen was constructed using OpenSees with the primary beams represented by force-based beam-column elements at ends and an elastic beam-column element in the middle. The fiber sections at the beam ends adopted a piecewise linear model with fatigue limits based on a linear cumulative damage rule. The material models were calibrated to reproduce the occurrence of local buckling and crack propagation observed in a beam-and-column subassemblage test. The numerical 4-story model was subjected continuously to the small to large ground motions recorded during the shake-table tests. In the first-round attempt, the simulated response agreed with the tests up to the first 100% motion. Although fatigue properties were introduced to the model, the simulated beams did not fracture but showed strength degradation due to local buckling.