Functional recovery time of low-rise concentrically braced frame buildings: Probabilistic assessment of footing size effects

A city’s capacity to withstand and recover from seismic events plays a crucial role in safeguarding the well-being of its residents. While numerous studies have investigated the recovery cost and time of buildings following earthquakes, the effects of soil and foundation have often been overlooked despite their known influence on seismic performance. This study addresses this gap by examining the possibility of optimizing the foundation size for low-rise concentrically braced frame (CBF) buildings, considering repair cost and recovery time as key performance indicators. For this purpose, one-, two-, and three-story steel buildings located in Vancouver, Canada, with X-bracing systems, are designed for two typical site classes, one representing stiff soil conditions near the site class C/D boundary, and the other soft soil conditions near the site class D/E boundary. Monte Carlo simulation is employed to incorporate uncertainties in the material properties, gravity loads, seismic demand, and the inherent damping of the structure. Nonlinear response history analyses are conducted at the design-level intensity using OpenSees. The foundation size, including footings that satisfy US design requirements as well as Canadian capacity-protected (CP) and not capacity-protected (NCP) options, is treated as the decision variable. The results indicate that the footing size significantly influences the seismic response mode of low-rise buildings, with peak floor acceleration emerging as the most influential engineering demand parameter affecting both repair cost and recovery time. The findings suggest that while the footing size has a negligible impact on the functional recovery time of buildings on soft soil, larger footings on stiff soil may result in extended recovery times. Although the performance difference between footing sizes is often small, the increase in cost for larger footings can be significant. Therefore, this study indicates that NCP footings (i.e. rocking foundations) may be the more advantageous choice for short-period CBF buildings. Keywords