Numerical analysis of special concentric braced frames using experimentally-validated fatigue and fracture model under short and long duration earthquakes

Abstract

Over the past decade, several long duration subduction earthquakes took place in different locations around the world such as Indonesia in 2004, China in 2008, Chile in 2010, and Japan in 2011. Long-duration and large-magnitude earthquakes are also possible to occur in the Cascadia subduction zone along the Pacific Northwest Coast of the United States. In this paper, numerical investigation was conducted to investigate the influence of earthquake duration on the structural response of steel special concentric braced frames (SCBFs). Calibration and validation of numerical models were achieved using results from recently completed shake table tests at the University of Nevada, Reno of three identical 1/2-scale one-story one-bay SCBFs under unidirectional short and long duration earthquakes. The objective of this paper is two-fold: (1) to use the experimental results to assess the suitability of current low-cycle fatigue models when incorporated into numerical models; (2) to utilize the calibrated numerical model in large number of simulations to extend and generalize the experimental results to quantify the effect of earthquake duration on SCBFs. For the latter, two suites of short and long duration ground motions were utilized to conduct incremental dynamic analysis (IDA) for the calibrated numerical models of the tested frames. The IDA, and resulting fragility curves, concluded that longer duration earthquakes result in 45% lower median displacement capacity, which could be regarded as premature low-cycle fatigue induced-failure of braces.