Structural Performance and Fragility Assessment of Elevated Residential Buildings During 2017-2018 Hurricanes in Texas and Florida

Elevating coastal houses on columns or piles is recognized as an effective technique for reducing the risks of flooding and storm surges. However, recent hurricanes have exposed a potential vulnerability in this approach, as many elevated residential structures sustained significant wind damage even at wind speeds below the current design level. Elevating a structure increases its exposure to stronger winds and leads to potential changes in the wind effects due to the air gap beneath the floor. However, there has been limited research comparing the performance of actual constructed elevated and slab-on-grade residential structures during realistic wind events. To fill this gap, authors utilized publicly available building performance datasets, collected by the Structural Extreme Events Reconnaissance (StEER) Network and others, to extract data on the performance of 851 elevated and 1536 slab-on-grade residential houses impacted by Hurricanes Irma, Harvey, and Michael. Effects of several key parameters were analyzed in terms of the intensity and distribution of the damage experienced by the different components. Furthermore, empirical fragility functions were developed for different roof shapes and cladding materials by combining the estimated wind speed that affected each structure and the assigned damage ratios for the roof and wall claddings. Analysis using the Wilcoxon rank-sum test demonstrated a statistically significant difference in the median wind speeds of various damage states of the components in both elevated and slab-on-grade houses. Additionally, a significant difference was observed in Texas slab-on-grade houses which experienced either no, minor, moderate, or severe damage, compared to their Florida counterparts. Results showed that elevated houses experience more damage than their slab-on-grade counterparts regardless of the roof shape, cladding materials, and construction age. Additionally, results showed that the elevated houses built in Texas exhibit the highest level of vulnerability among the various housing groups studied. Specifically, the percentage of elevated houses in Texas that experienced destroyed damage state surpassed those of slab-on-grade houses in Texas and elevated houses in Florida by 343% and 166%, respectively. The paper identified several knowledge gaps, and it emphasized the need for further experimental tests of building components and different building geometries to improve existing risk models.