Seismic Performance of Braced Steel Frames Under Long Duration Ground Motions

Abstract eng:
Over the past decade, several long duration subduction earthquakes took place in different locations in Chile and Japan. These events highlighted the importance of comprehensive investigation of the effect of the ground motion duration on structural performance. This paper presents a preliminary computational modeling developed in the OpenSees framework to assess the seismic performance of concentrically braced frames (CBF) under long duration earthquakes. The objective of the study is to explore the effect of low-cycle fatigue on structural members and the accumulated damage as related to the ground motion duration. Nonlinear time history analysis was conducted using subduction and crustal ground motion records. A calibrated model was used to compare between the behavior of a single-story X-braced CBF and a typical six-story frame under both types of ground motions. It was found that the effect of duration on the nonlinear seismic response is particularly significant in terms of the strain accumulated in the braces causing induced low-cycle fatigue fracture. Therefore, particular attention should be given to the effect of earthquake duration when designing CBF buildings located in the proximity of subduction zones and do not rely only on response spectral values in predicting the structural response.

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