Structural behaviours of circular hollow section T-joints subjected to elevated temperature

• Main Author: Nguyen, Minh Phuong.
• Other Authors: Fung Tat Ching
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Civil engineering::Structures and design
• Online Access: http://hdl.handle.net/10356/53916
• Institution: Nanyang Technological University

The research on structural behaviour of circular hollow section (CHS) joints at elevated temperatures was motivated by the need of fire resistance estimations for performance-based approach of tubular structures. This thesis presents a study on structural behaviour of CHS T-joints in four parts where a set of CHS T-joints subjected to (i) brace axial compression; (ii) in-plane bending; and (iii) a standard ISO-834 fire curve. Test observations and failure mechanisms in the first three parts provide an input for the fourth part (iv) where an analytical model of CHS T-joint was developed using yield line approach. The first research aim is to understand the mechanical behaviour and failure mechanism of the joint without any heat transferred effect such as thermal restraints, or a fast-/slow-increasing temperature rate. Therefore, in Parts (i) and (ii), the investigations were done in isothermal conditions where the temperatures were kept constant and the CHS T-joints were loaded to fail. The second research aim is to estimate the fire resistance of the joints in a standard fire condition. Hence, in Part (iii) the joints subjected to brace axial compression and in-plane bending were tested in ISO-834 fire condition. This is a standard transient condition where all heat transferred effects of a standard growing fire were included. For each of the initial three parts, numerical models were developed individually due to the differences in failure modes and test set-up. However, due to a similarity in the joint geometry and material in this study, a typical 8-nodes thick shell element model was used for all joints. ABAQUS v6.9-1 was used as a numerical environment. In each part, the numerical models used test data as verification sources, and then these models were employed to produce in-depth analysis. The attempt to develop the joint analytical models was presented in Part (iv). Folding mechanism was proposed as a combination of plastic moments, ovalisations and tensile membranes. Based on the mechanism, the joint ultimate strength can be determined using yield line approach. Although there are deviations in model validation, this is the first attempt to incorporate all mechanical behaviour of CHS T-joints into a close-form solution. Some limitations and improvements of the models were found and recommended for future study. The fourth part also introduces a reduction factor, k, which is used with the analytical solution for predicting joint strength at elevated temperatures.