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Abstract

A new method of structural stability analysis which accounts for the spread of inelasticity along structural members is presented in this thesis. This method is called the inelastic zone method and is employed here to investigate the behaviour of metal plane frames loaded to failure. For a given loading on a plane frame, the inelastic zones which may be present along the frame members are identified without a finite discretization of the members and their cross-sections. Account is taken of any initial member curvature in determining the tangent force-displacement relationships for the members. A bilinear stress-strain relationship for the material is adopted. The equation for the deflection curve for an inelastic zone which is similar to that for the deflection curve for an elastic beam-column is assumed, the main difference being that this assumed equation contains additional terms for satisfying curvature boundary conditions. The accuracy of this equation is examined in a Parametric Study. In this thesis, rectangular and I-shaped cross-sections have been considered for the frame members. The tangent force-displacement relationships so determined at a given load level are used to analyse the plane frame using the stiffness method of structural analysis in which account is taken of the changes of geometry of the frame. By repeating this procedure for increasing loads, the stable equilibrium path for the frame can be traced.

Experiments were conducted on two portal frames built-up from mild steel members having rolled I-shaped cross-sections. This was aimed at building a model with realistic geometrical imperfections and residual stresses. The results obtained are compared with those predicted by the proposed method and good agreement is obtained for ultimate loads, deflections and spread of plasticity.

Frame failure loads obtained by theoretical methods and experiments reported in the literature are compared with those obtained by the inelastic zone method. Good agreement is obtained while the inelastic zone method is shown to give lower-bound values of frame failure loads.

Recommendations for the design of metal plane frames are also given. In addition, a new, simplified method of plane frame design which avoids the computation of frame failure loads and member effective lengths but considers an estimated ultimate strength of each member cross-section based on the results obtained from a non-linear, elastic analysis of the frame subjected to the working loads is presented. This method is called the limiting moment method and can be applied to all types of plane frame under general loadings. Examples which illustrate the application of this method to frame design are given.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TH Building construction
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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