Non-linear analysis of steel frames under non-proportional and fire loads

Abstract

This thesis addresses the influence of non-proportional loads on the non-linear and advanced analysis of semi-rigid steel structures and the applications of this modern analysis technique in structural fire engineering. To investigate the first topic, the Refined Plastic Hinge method, which is modified to allow for non-proportional loads in this study, is used for numerical analyses. This Refined Plastic Hinge method is adopted because it is believed to be the most efficient and practical tool for non-linear analysis that can be applied in design practice. The numerical results show that the effect of non-proportional loading is significant and cannot be ignored. The second topic involves the work undertaken to modify the Refined Plastic Hinge method so its application can be extended for studying the fire effect in steel structures. In parallel, a newly proposed method, namely the Sectional Stiffness Integration method, is developed to evaluate the response of steel structures in fire. During normal conditions, the performance of this proposed method is validated and found to have similar efficiency and to be more accurate than the Refined Plastic Hinge method. During fire conditions, the accuracy and robustness of these two numerical methods are demonstrated while compared against other experimental and numerical data. Using this Refined Plastic Hinge method, a study on the behaviour of semi-rigid frames and steel columns under fire is also included in this thesis.