Seismic risk assessment of a steel building supported on helical pile groups

Designing structures to be the least vulnerable within earthquake-prone areas is a serious challenge for structural engineers. One common and useful tool that structural engineers use to predict the vulnerability of a structure during an earthquake is a fragility curve. However, most structural fragility curves do not take into consideration the contribution of pile foundation systems in the structural vulnerability. Therefore, this study aims to modify existing fragility curves of a six-story fixed-base steel frame hospital building with buckling-restrained braces, to incorporate the effect of helical pile group behavior on the fragility of the structure. To that end, a finite element model of the investigated structure was modified with results from a full-scale shake table test performed on two groups of helical piles embedded in dense sand supporting a superstructure. The primary results show that fixed-base design may not be conservative for all conditions and soil–foundation interaction should be considered when creating fragility curves, especially for a stiff structure on soft soils where a high-intensity earthquake is anticipated.