Browsing by Author "Oosthuizen, Frederik du Toit"

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    Probabilistic based evaluation of the structural reliability achieved for a typical building designed according to SANS 517:2009 and SANS 10162- 2:2010
    (Stellenbosch : Stellenbosch University, 2011-12) Oosthuizen, Frederik du Toit; Dunaiski, P. E.; Viljoen, Celeste; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: This study aims to perform a quantitative probabilistic based evaluation of the reliability achieved in the design of Light Steel Frame Buildings (LSFB) when designed according to the loading code, SANS 517:2009 and the new design code for cold formed steel sections, SANS 10162-2:2010. The evaluation was done as follows: A specific structure, chosen and designed according to the specifications given in SANS 517:2009, was modelled in a structural analysis program. From the analyses done it was possible to identify the most critical element for given failure modes. Spread sheets according to SANS 10162-2:2010 were developed to calculate the resistance or design values for the different failure modes. By using a First Order Reliability Method (FORM), the reliability index for each failure mode could be calculated and evaluated in three different ways. Firstly, the reliability margin implied by the design load was evaluated. It was assumed that the resistance of the profile had a deterministic value while the loads applied to the structure were taken as probabilistic, i.e. following their known distribution functions. From this evaluation it was found that the necessary level of reliability was achieved for all failure modes. Secondly, the reliability margin implied by the resistance of the profile was evaluated. The resistance of the profile was taken as probabilistic with a distribution function that could be determined from the known distribution functions of the profile parameters responsible for the capacity of the profile. The loading was assumed to have a single deterministic value. From this evaluation it could be seen that a very low level of reliability was achieved for the failure modes of shear working in on the strong axis of the profile as well as interaction between bending and axial load. This is due to the strong dependence of this failure mode to the thickness of the profile, to which no partial factor is applied in the design process. Thirdly, the reliability margin implied by both the resistance and loads was evaluated. In a real life situation both loads and resistances would have variability. The resistance and loading values were taken as probabilistic with their known distribution functions. From this evaluation it was found that the necessary level of reliability was only achieved for shear working in on the weakaxis and axial load. All other failure modes achieved a level of reliability slightly lower than the target level of reliability for South Africa. The stiffening effect of wall cladding elements were not taken into account in the analysis. The reliability of connections was also not evaluated. It can be concluded that the element reliability achieved through the use of above-mentioned codes seems to be slightly less that desired. There could be an argument for recalibrating the partial factors to achieve the desired level of element reliability. However, the cladding elements provide significant additional stiffness to the structure and there is no immediate cause for stiffness concern. Future studies should aim to quantify the contribution that the cladding elements make to the overall structural reliability. The influence of connections reliability should also be investigated.