A. Baskaran, Ph.D., S. Molleti, Ph.D., S. Ko, M.Eng, and L. Shoemaker, Ph.D.
Journal of Architectural Engineering, May 2011
Abstract
Wind forces remain one of the most common factors in roof failures, inflicting considerable damage every year, even to new roof structures. Metal roofs are one of the popular low‐sloped roof assemblies. Based on their layout, they can be categorized as either composite or non‐composite assemblies. In North American practice, five main test procedures — ASTM E1592, ANSI/FM 4474, UL 580, UL 1817 and CSA A123.21‐04 — are used to determine the wind uplift performance of metal roofs. The fundamental differences between these test protocols lie in the way they represent wind effects on the performance of metal roofing systems. Of the five, CSA A 123.21‐04 is the only one that assesses the wind uplift resistance under dynamic wind load conditions. To evaluate the wind uplift performance of non‐composite and composite metal roofing assemblies, eight assemblies with two different types of panels — SNAP‐IT and MR‐24 — were tested using the CSA A123.21‐04 dynamic test protocol. Relating air intrusion characteristics of the subsurface components to panel behavior, this paper shows how composite assemblies resist wind uplift pressures better than non‐composite assemblies. The paper reveals that the greater the air intrusion resistance of the sub‐surface components in composite assemblies, the higher the suction resistance, the lesser the panel deflection, the lesser the stress on the panels and the higher the wind uplift resistance.
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