Master of Engineering Science
Civil and Environmental Engineering
Dr. Greg Kopp
Dr. Ayman El Ansary
Wood-frame residential roof failures are among the most common and expensive types of tornado damage. Hip roofs are commonly understood to be more resilient during extreme wind in relation to gable roofs. However, inspection of damage survey data from recent tornadoes has revealed a previously unstudied failure mode in which hip roofs suffer partial failure of the framing structure. This research focuses on proving the concept of framing failures in hip roofs. Evidence of partial framing failures and statistics of their occurrence are explored and discussed, and common roof design and construction practice is reviewed. Two-dimensional finite element models are developed to estimate the element-level load effects on hip roof trusses and stick-frame components. Following model development to estimate the maximum demand on the framing elements, the elements’ capacities are estimated. The likelihood of failure in each member is defined based on relative demandto-capacity ratios. Trussed and stick-frame structures are compared to assess the relative performance of the two types of construction. The present analyses verify the common understanding that toe-nailed roof-to-wall connections are likely to be the most vulnerable elements in a wood-frame roof. However, the results also indicate that certain framing members and connections display significant vulnerability under the same wind uplift, and the possibility of framing failure is not to be discounted. Furthermore, in the case where the roof-to-wall connection uses hurricane straps, certain framing members and joints become the likely points of failure initiation. The analysis results and damage survey observations are used to expand the understanding of wood-frame residential roof failures, as they relate to the Enhanced Fujita Scale, and provide assessment of potential gaps in residential design codes.
Stevenson, Sarah A., "Analysis of Framing Failures in Wood-Frame Residential Roofs Under Wind Load" (2017). Electronic Thesis and Dissertation Repository. 4851.
Available for download on Saturday, September 01, 2018