A theoretical and experimental study of the effect of the spread of plasticity on the behaviour of beam-columns and on the non-linear analysis of steel frames

El-Dib, Mohamed El-Said Abou-Hashem (1988) A theoretical and experimental study of the effect of the spread of plasticity on the behaviour of beam-columns and on the non-linear analysis of steel frames. University of Southampton, Doctoral Thesis.

Abstract

Plastic theory is now widely used for the design of building structures. Consequently, the prediction of the real behaviour of structures up to collapse, has been objective of many studies. The aim of this study is to develop a theoretical approach, based on the matrix stiffness method to the problem of the second-order elastic-plastic analysis of steel structures considering the effects of the spread of plasticity. In doing this, a new analytical approach to the calculation of the instantaneous stiffness and carry-over factors of elastic or inelastic, prismatic and non-prismatic, isolated beam-columuns was developed. In addition, a method was derived for the calculation of the exact moment-curvature-thrust relationship for partially plastic I- and box cross-sections. In order to verify the validity of the approach, eight major tests were carried out on isolated members formed from rectangular hollow sections. Measurements were taken through the elastic and inelastic stages, up to failure. The experimental results obtained confirmed the proposed theoretical method and excellent accuracy was achieved. Non-linear elastic and elastic-plastic analyses of steel structures are described. The computer program based on these is also capable of linear elastic and elastic-plastic analysis. Although there was no opportunity to carry out tests on frames, the method was checked against the experimental results from two frames tested by others. Furthermore a frame with uniformly distributed load members, and fifteen-storey rectangular and irregular frames were analysed. The results obtained agreed closely with the experimental results and with the results of other analyses. It was found that although the effects of spreading plasticity in an isolated member are large, in big structures the effect on the load carrying capacity is small. However, it was also found that deflection can be affected and that the distribution of plastic hinges at collapse is modified. The thesis also draws attention to possible developments in the analysis to include the effects of strain hardening and residual stress and shows how it can be extended to the analysis of reinforced concrete structures. (D82545)

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