Comparing responses of special and intermediate moment frames under repeated earthquakes

Steel moment-resisting frames (MRFs) are designed to resist a design-level single seismic event. However, every earthquake may be accompanied by several foreshocks or aftershocks. The cyclic deterioration of structural elements during early earthquakes may cause the lateral-load-resisting system to collapse under the mainshock or aftershocks. The differences in the seismic performance of special and intermediate MRFs (here called SMFs and IMFs, respectively) subjected to single and multiple earthquake events were investigated. For this purpose, four perimeter steel MRFs with four and eight storeys were designed and subjected to 22 synthesised multi-record earthquake events. The non-linear modelling technique adopted accounts for the cyclic deterioration of structural elements, which is a key parameter in the evaluation of seismic performance under sequential earthquakes. The results showed that structural collapse capacity may be reduced considerably if the structure is subjected to foreshock and aftershock events in addition to the mainshock. In addition, it was found that, for the IMF models, the switch from the life safety (LS) limit state to the collapse prevention limit state was immediate. Therefore, the design of IMFs for the LS performance level may result in a substantial risk of collapse when the structure is exposed to repeated earthquakes.

Automated summary

Steel moment-resisting frames (MRFs) are designed to resist seismic events, but may collapse under the cyclic deterioration of structural elements during early earthquakes; exposure to foreshocks and aftershocks can significantly reduce structural collapse capacity.