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Title: Design of structural steel elements with the Continuous Strength Method
Author: Liew, Andrew
ISNI:       0000 0004 5348 7158
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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The current practice of ultimate limit state design for steel structures involves an elastic--perfectly plastic material model and the classification of cross-sections into discrete behavioural classes. This leads to a design philosophy which is simple, but generally over-conservative. The Continuous Strength Method is a strain based design approach which allows for the beneficial influence of strain hardening. At the core of the method is a base curve which relates the deformation capacity of a cross-section to its cross-section slenderness. Deformation capacity is defined through a strain ratio, which is the ratio of the maximum strain that a cross-section can endure to its yield strain. The formulation for the base curve was derived by means of stub column and bending tests collected from the literature. Knowing the limiting strain and assuming plane sections remain plane, the resistance of cross-sections to combinations of axial load and bending moments can be calculated by integrating the stresses arising from a suitable strain hardening material model over the area of the cross-section. Analytical and design expressions have been developed, and the resistance predictions for open and closed cross-section shapes have been compared with existing collated test data, and shown to give additional capacity over current design approaches, with a reduction in scatter and a more consistent method. Beyond the analysis of the cross-section, the method has been extended to the global instability of pin-ended columns by utilising moment--curvature--thrust curves. The curves were paired with an assumed buckled displacement shape to find applicable equilibrium configurations, and to extract the peak axial loads for producing buckling curves. The column buckling curves showed two distinct regions based on the global slenderness of the column. Firstly a region of global-dominated failure, where the columns failed by a loss of overall flexural rigidity, and secondly a local-dominated failure region, where the mid-height cross-sections failed by local buckling. The local cross-section failure mode allowed for axial loads greater than the cross-section yield loads. The column buckling curves were found to be dependent on the initial out-of-straightness, the cross-section geometry and the material yield stress. An experimental program provided insight into the cross-section resistance of hot-rolled rectangular hollow sections (RHS). The experiments included 32 material tensile coupon tests, eight stub column tests and four simply supported beam tests, and exhibited little strain hardening. Overall, a series of developments to a strain based approach for steel structures has been presented, and areas for future developments have also been highlighted.
Supervisor: Gardner, Leroy Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available