Performance evaluation of mechanically attached roofing systems

Roofing system is an integral part of a building envelope. Keeping the roofs in place against high wind events is a challenging task for architects and roof designers. There are two stages in the design process: first, a comprehensive understanding of the wind induced loads on the roof system and, second, an accurate estimation of the system response to the induced wind loads. The present study contributes to an ongoing research project at the National Research Council Canada in the evaluation of Mechanically Attached Roofing Systems (MAS) for wind uplift design. Accomplishments are grouped in two tasks. Task 1, applied finite element methods to investigate whether an analytical method can be used to predict fastener loads based upon uplift pressures and chamber geometry. Task 2, developed an experimental procedure to quantify the air leakage rate and identified its impact on the wind uplift resistance. The aspect ratio of the testing chamber plays a critical role in the evaluation of roofing system response. By applying finite element modeling the table size effect was investigated and the numerical results were benchmarked with experimental data. The validated model was further used to identify the required table width. It was found that an increase in the table width beyond required table width did not significantly change the system response. The required table width depends mainly on two system parameters, namely, fastener row spacing and fastener spacing. Based on the parametric investigation generalized correction factor curves were developed such that the roofing designer can apply these factors irrespective of the investigated table width. In MAS, the fluttering or "billowing" action of the membrane draws air in to system, thereby affecting system's wind uplift performance. There is no standard specification or test method available to quantify the air leakage rate. By designing an experimental setup, systems with and without barriers were investigated. Data clearly indicate that systems without barrier had a high rate of air leakage, compared to systems with barrier. With the quantification of air leakage, its impact on the wind uplift resistance was also evaluated under a dynamic wind environment. Improvement in wind uplift resistance was evident for systems with barriers