Static strength of tubular T/Y-joints reinforced with collar plates at fire induced elevated temperature

摘要

This paper aims to investigate the structural behavior of T/Y-joints reinforced with collar plates subjected to compressive loading at fire induced elevated temperatures. At the first step, a finite element (FE) model was developed and verified by results of six experimental tests carried out in the present author's previous study. Also, the FE model was validated using experimental data reported in available research works. At the next step, a total number of 360 FE analyses were performed to investigate the effect of elevated temperatures, dimensionless geometrical parameters (eta, tau(c), beta, gamma), and brace inclination angle (theta) on the initial stiffness, ultimate strength, and failure mechanisms. The joints were analyzed under axially compressive load and five different temperatures (20 degrees C, 200 degrees C, 400 degrees C, 600 degrees C, and 800 degrees C). Results showed that at elevated temperatures, the increase of the collar plate length and thickness significantly results in the increase of the initial stiffness. Also, at elevated temperatures, the ultimate strength of T/Y-joints reinforced with collar plate can be up to 254% of the ultimate strength of the corresponding unreinforced joint. Despite this significant difference between the static strength of unreinforced and collar plate reinforced T/Y-joints at elevated temperatures, there has not been any study on the initial stiffness and ultimate capacity of the T/Y-joints reinforced with collar plate at elevated temperatures. Also, there is no design equation for determining the ultimate strength of the collar plate reinforced T/Y-joints at elevated temperatures. Therefore, the results of the parametric study were used to develop a design formula, through nonlinear regression analyses, to calculate the ultimate strength of tubular T/Y-joints reinforced with collar plates subjected to axially compressive loading at elevated temperatures.