Thesis (MScEng)--Stellenbosch University, 2011. / 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 contribute
to extreme load combinations. Frequently recorded failures on roof structures suggest that
either the loads are underestimated or the resisting capacity of the roof coverings is
overestimated. The focus of this study is directed on the latter, determining the effective
resistance 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 involves
experimental tests on certain configurations with two or more spans. The structural test set-up
is loaded with sandbags until failure is reached.
For the design of roofing systems, design tables are used that list the maximum allowable
purlin spacing. The purlin spacing is presented in the form of a fixed value in units of length
and is shown independent of a UDL that the roof needs to be designed for. The need to a new
approach to determining the resistance of roof covering systems was identified.
The resistance of roof coverings for the Ultimate Limit State (ULS) and the Serviceability Limit
State (SLS) depends on a number of parameters such as the bending resistance, the stiffness of
the sheeting in bending and the carrying capacity of the fastening system. To evaluate these
structural 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-up
consists of four different configurations, each specifically schematized to evaluate a certain
structural design parameter. The magnitude of the structural design parameters depends on
the applied UDL and the span length, which is the distance between consecutive supports of
the sheeting system. Therefore, by using the structural design parameters determined
experimentally, a set of design tables could be generated. The design tables produce the
maximum allowable span length of a roofing system that uses a desired UDL as a variable. By
using the design tables, the purlin spacing for any roof structure can be calculated given its
design loading combination. The calculated purlin spacings are now a function of the basic
parameters that determine the resistance of the roof sheeting. / AFRIKAANSE OPSOMMING: Geen opsomming
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18053 |
| Date | 12 1900 |
| Creators | Kretzschmar, Gunnar |
| Contributors | Dunaiski, P. E., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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