Accounting for moment-rotation behaviour of connections in portal frames

Albertyn, Heindrich L. ; Haas, T. N. ; Dunaiski, Peter E. (2014-04)

CITATION: Albertyn, H. L., Haas, T. N. & Dunaiski, P. E. 2014. Accounting for moment-rotation behaviour of connections in portal frames. Journal of the South African Institution of Civil Engineering, 56(1):69-76.

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Portal frames are steel structures used to construct industrial buildings. Conventional analysis techniques used by practising engineering professionals assume that the eave, ridge and base connections are either infinitely rigid or perfectly pinned. This approach leads to less accurate analysis of the displacement behaviour of portal frames when subjected to external loading. Portal frames must therefore be analysed with rotational springs at all connections to yield accurate displacement behaviour. This investigation focused on determining the accuracy and economic feasibility of modelling portal frame connections with rotational springs. The rotational spring stiffnesses of all connections were required before the portal frame could be analysed in a second-order two-dimensional non-linear analysis. The rotational spring stiffnesses unique to each connection were determined from the moment-rotation behaviour obtained from a series of finite element analysis simulations of each connection. Thereafter these stiffnesses were used to determine the vertical and horizontal displacements of the portal frame. These displacements were compared with experimental test results. The reasons for the discrepancies between the numerical and experimental results were investigated through a sensitivity analysis. The findings suggest that it is not computationally feasible to analyse portal frames with rotational springs, even though the model’s predicted results are more accurate than those of conventional analysis using rigid and pin connections.

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