Mechanics and test study of flexible membranes ballooning in three dimensions

Numerous enclosure wall systems employ membranes that are not fully adhered, common examples being mechanically attached housewraps in screen-type exterior wall systems. Many roofing systems also incorporate membranes that are not fully adhered such as mechanically fastened single-ply membranes. Under a negative air pressure differential caused by wind suction, these wall and roof membranes can deform or balloon. Ballooning of the membrane affects many aspects of its performance. For instance, it changes the volume of the air chamber in screen-type wall systems and therefore, affects both the extent of screen pressure moderation and the nature of ventilation within the wall. In case of the single-ply roofing membrane, excessive ballooning can tear or rupture the membrane at the mechanical fastener location and therefore fail the membrane as the primary waterproofing component in the roofing system. This paper develops the structural mechanics for flexible membranes ballooning in three dimensions under a negative air pressure differential. The governing differential equation is derived and solved numerically. A second-order paraboloid of revolution is assumed to describe the ballooning shape. A series of physical tests were conducted to confirm that the ballooning shape follows the second-order paraboloid of revolution and compare the model predict with the test data.