Seismic response of mega buckling-restrained braces subjected to fling-step and forward-directivity near-fault ground motions

Special characteristics of earthquakes in the near-fault regions caused failures for many modern-engineered structures. Fling-step and forward-directivity are the main consequences of these earthquakes. High-amplitude pulses at the beginning of the seismograph have been obviously presented in forward-directivity sites. These pulses have high amount of seismic energy released in a very short time and caused higher demands for engineering structures. Fling-step is generally characterized by a unidirectional large-amplitude velocity pulse and a monotonic step in the displacement time history. These monotonic steps cause residual ground displacements that are associated with rupture mechanism. In this paper, the seismic performance of steel buckling-restrained braced frames with mega configuration under near-source excitation was investigated. Fourteen near-fault records with forward-directivity and fling-step characteristics and seven far-faults have been selected. Nonlinear time-history analyses of 4-story, 8-story, 12-story and 15-story frames have been performed using OpenSees software. After comparing the results, it is shown that, for all frames subjected to the selected records, the maximum demand occurred in lower floors, and higher modes were not triggered. Near-fault records imposed higher demands on the structures. The results for near-fault records with fling-step were very dispersed, and in some cases, these records were more damaging than others. Copyright © 2014 John Wiley & Sons, Ltd.