SUMMARYSpecial 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. Highamplitude pulses at the beginning of the seismograph have been obviously presented in forwarddirectivity 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 largeamplitude 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.

This paper has two main objectives. The first objective is to compare the dynamic behavior of mega shapememory alloy (SMA) braced frames subjected to far-fault and near-fault ground motions. Therefore, four mega SMA braced frames with various stories located in the vicinity of an active fault were considered. Fourteen near-fault records with two well-known characteristics of these records, i.e. forward directivity and fling step, were selected to test near-fault earthquake characteristics. Furthermore, other seven farfield records were selected for comparison. Through the nonlinear dynamic analyses, the results showed that for high-rise frames, the near-fault earthquakes resulted in more demands than the far-field, but for low-rise frames, far-fault records imposed more demands. It was also found that mega configuration and SMA stiffening at large strains played key roles in seismic vibration control of frames. The second objective of this paper is to study the superior performance of SMA braces over the buckling restrained braces by exploiting the super-elastic characteristic of the SMA. Identical buildings equipped with buckling restrained braces were also studied for comparison purposes. The results revealed the excellent performance of SMA braces under near-fault records by reducing both interstory drift and residual displacement of the top floor.

No abstract

No abstract

No abstract