Development and Validation of 3D Composite Structural Elements at Elevated Temperatures

A three-dimensional (3D) eight-noded brick element, which is capable of representing the performance of composite structures subjected to 3D stress conditions at ambient and high temperatures, has been developed and incorporated into a finite-element analysis program Vulcan. In the formulation of this element, geometric nonlinearity, material nonlinearity, material degradation, and thermal expansion at elevated temperatures have been taken into account. The von Mises and Drucker-Prager theories were chosen as the 3D failure criteria for steel and concrete, respectively. In particular, a series of postfailure criteria and corresponding 3D constitutive relations for concrete at high temperatures were defined in this study. The accuracy and efficiency of this newly developed structural element was verified against the results from a number of tests on composite structures subjected to 3D stress conditions at both ambient and elevated temperatures. The proposed 3D structural element can be used to model a large range of composite structures in fire, and perform more detailed studies on them.