M.Ing. (Civil Engineering) / Cold-formed steel lipped channels are among the most used sections, as framing members in the building construction industry, especially in residential, commercial and industrial buildings. In portal frame, when lipped channels are used as main frame members, they are usually restrained from the top flange through angle-cleat to prevent lateral-torsional buckling. This restraining system works together with an additional restrain system called fly-bracing. Drilling a bolt-hole or welding the angle cleat onto the flange of the main frame weakens its bearing length. Additional disadvantage of this restraining system is the fabrication costs of providing fly bracing. However, past research into lateral-torsional buckling of cold-formed steel lipped channel sections are limited. Therefore this study investigates a restrain that avoids bolt holes and welding in the top flange of the rafter, and the use of fly bracing. In the first phase of this research, tensile coupon tests of the three cross-sections are conducted to obtain the material properties. The elastic modulus and yield strength of the cold-formed steel used are determined from stress-strain relationship. These properties are used to calculate the code-predicted lateral-torsional buckling moment resistance. The second phase of this study involves a series of experiments on the lateral torsional instability of single cold-formed channels. The channels are restrained by a purlin – angle cleat connection and are subjected to a two point loading system in order to simulate a distributed load. Failure of the channels occurred by local buckling of the compression zone of the flange and web and lateral torsional buckling of the channels between points of lateral support. Tests have shown the purlin – angle cleat connection to be capable of restraining the frames from failing due to lateral-torsional buckling. This eliminates the idea of using fly-bracings, as is normally done in practice to restrain torsional instability. The results from the experimental study do agree well with those predict by the South- African code, SANS 10162-2: 2005. This research presents the details and results of the experimental study including a comparison of results with the South-African code SANS 10162-2: 2005 predictions. It also presents the recommendations made regarding the use of a numerical model study in order to compare the results with those from the experiments.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:11218 |
| Date | 26 May 2014 |
| Creators | Bukusa, Gregoire Mulumba |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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