Seismic performance assessment of steel frames with slack cable bracing systems

Abstract

Slack cable collapse prevention system is a cost-effective and simple method for seismic upgrading of existing structures. In this study, the effectiveness of adding slack cables to 2, 4, 8, and 12-story steel frames are assessed. The pushover analyses were performed to evaluate the general behavior of the original and braced frames. Considering 22 pairs of far-field ground motion records per FEMA P695, the nonlinear time-history analyses, as well as Incremental Dynamic Analyses (IDAs), were conducted. The maximum compression force of the first story columns, base shear demand, and the Collapse Margin Ratio (CMR) were determined and compared for original and braced frames. The fragility curves were developed and compared for the structures. Obtained results show that the slack cables postpone the collapse of the frames without increasing the initial stiffness of the structure. The average of maximum values of column axial force for the frames with slack cables are close to original frames, while it has a considerable increase in typical cable brace system cases. All original frames exceed the 10% probability when subjected to Maximum Considered Earthquake (MCE). However, the probability of collapse for the braced structures in MCE decreased significantly to less than 10%. A significant improvement in the collapse safety could be observed in the braced frames. The slack cable technique has demonstrated almost similar performance to the typical cable braces and even superior protection in terms of structural column axial forces and base shear.