The experimental determination of structural design parameters for roof covering systems

[摘要] ENGLISH ABSTRACT: All structures are designed for a particular set of load combinations. For roof structures the critical loading combinations are predominantly wind actions. The accumulative effect of wind actions, by wind entering through dominant openings to exert pressure on the inside of roof structures together with the suction of wind vortices on the outside of the roof, can contributeto extreme load combinations. Frequently recorded failures on roof structures suggest thateither the loads are underestimated or the resisting capacity of the roof coverings isoverestimated. The focus of this study is directed on the latter, determining the effectiveresistance of roof coverings in the form of sheeting against a Uniformly Distributed Load (UDL) such as wind actions.To determine the carrying capacity of a roofing structure, the standard approach used involvesexperimental tests on certain configurations with two or more spans. The structural test set-upis loaded with sandbags until failure is reached.For the design of roofing systems, design tables are used that list the maximum allowablepurlin spacing. The purlin spacing is presented in the form of a fixed value in units of lengthand is shown independent of a UDL that the roof needs to be designed for. The need to a newapproach to determining the resistance of roof covering systems was identified.The resistance of roof coverings for the Ultimate Limit State (ULS) and the Serviceability LimitState (SLS) depends on a number of parameters such as the bending resistance, the stiffness ofthe sheeting in bending and the carrying capacity of the fastening system. To evaluate thesestructural parameters, experimental tests were performed. A full-scale experimental test setup,capable of simulating a UDL on roof sheeting, was developed. The experimental test set-upconsists of four different configurations, each specifically schematized to evaluate a certainstructural design parameter. The magnitude of the structural design parameters depends onthe applied UDL and the span length, which is the distance between consecutive supports ofthe sheeting system. Therefore, by using the structural design parameters determinedexperimentally, a set of design tables could be generated. The design tables produce themaximum allowable span length of a roofing system that uses a desired UDL as a variable. Byusing the design tables, the purlin spacing for any roof structure can be calculated given itsdesign loading combination. The calculated purlin spacings are now a function of the basicparameters that determine the resistance of the roof sheeting.

[发布机构] Stellenbosch University