Inelastic Response of Simple Steel Trusses under Heating and Cooling

• Main Authors: Kai-Yuan Chen, 陳顗元
• Other Authors: 楊永斌
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/51136988416898421643

碩士 === 國立臺灣大學 === 土木工程學研究所 === 103 === Nowadays, due to the general use of steel structures in constructions and the high thermal conductivity, especially being compared with concrete, there are more and more emphasis on the designing and construction of steel works. When fire attacks, it causes elevated temperature, which makes the strength of materials and structures reduced, and causes large deformation. The purpose of this thesis is to theoretically discuss the elastic and inelastic behavior of structure under fire attack. The research works are divided into theory formulation and numerical simulation. In order to consider the softening of materials, the reduction factors based on Eurocode 3 are adopted. At first, taking a two-member truss for example, according to the simplicity of geometry and the use of Total Lagrange formulation enhanced with the rigorous formulation of stress-strain relation, we’re able to establish the equilibrium equations by the deformed configuration. Then, the analytical solutions are obtained with the truss under fire condition. Two kinds of loadings are considered, i.e., trusses under constant temperature but increasing loads, and trussed under constant loads but rising temperature. By the two different kinds of loading conditions, the postbuckling path can be built under various temperature or loads, and the critical load and temperature will be obtained, respectively. Besides, both elastic and elastoplastic materials are considered in investigating the effect of material yielding on the critical loads and critical temperature. Numerical approach is also presented. The finite element method is adopted to study the behavior of complicated truss structures. The generalized displacement control (GDC) method is applied as the scheme for incremental-iterative analysis to overcome the numerical instability caused by the limit points. The analytical solutions presented herein serve as the benchmarks for calibration of the accuracy of general finite element procedures in analyzing structures under fire conditions. The inelastic behavior of steel trusses cooled down from a heating stage is investigated by using the concept of instantaneous modulus, and taking the effect of plastic strain into consideration. The permanent deformation and member stress solved in this study are available to be used in the assessment of steel structures reusability and safety after a fire attacks.