Date of Award
2006
Degree Type
Thesis
Degree Name
Master of Engineering Science
Program
Civil and Environmental Engineering
Abstract
Rainwater on a large flat roof ponds, intensifying the load at the most critical location to risk instability and collapse of the roof. The current specifications in the National Building Code of Canada are based on 35-year old research and the current state of knowledge is unsatisfactory. In particular, residual stresses that may cause premature yielding of steel members are not considered in the current design criteria. This research presents a ponding map of Canada based on the relative magnitudes of snow and rain load alone that identifies Vancouver Island, Calgary, southwestern Ontario and southern Nova Scotia as regions where flat roofs are particularly susceptible to ponding failures. It summarizes a study on the impact of residual stresses on the secant stiffness of W-shapes. An analytical tool was developed to investigate current ponding criteria considering the effects of residual stresses, beam camber, joist camber, rainfall intensity, and member stiffnesses (serviceability limit states) on the performance of a typical simple-span roof system in Calgary. Finally, Gerber roof systems, which have different deflection characteristics than simply supported systems, were investigated. An example iterative calculation is provided to illustrate ponding calculations for a typical Gerber system, whereby water from one span can flow towards the adjoining span potentially overloading the span and initiating a structural collapse.
Recommended Citation
Praught, Derek C., "DESIGN FOR PONDING OF RAINWATER ON LARGE FLAT STEEL ROOFS" (2006). Digitized Theses. 5022.
https://ir.lib.uwo.ca/digitizedtheses/5022