Model-Based Elastic and Thermal Compensation for Developing Demand-Capacity Curves of Columns under Elevated Temperature

This paper presents the generation of demand-capacity curves for columns under compression subjected to elevated temperatures using hybrid fire simulation. Initial axial stress and axial restraint against thermal expansion are the two criteria used to quantify the boundary conditions for such columns in an actual structure. Initial stress levels of 0.1 to 0.9 times the design compressive stress at an interval of 0.1 are used for an axial restraint ratio of 2%, 5%, 10%, and 15% with respect to the specimen stiffness. Steel coupons designed to have a slenderness ratio (KL/r) of 20 are used as experimental substructures, which are heated from room temperature to 800°C for each test using a split-chamber electric furnace. A computer-model numerical spring is used as the numerical substructure for the hybrid simulation, representing the axial restraint provided by an actual building onto the column. A model-based compensation scheme is used to compensate for the elastic and thermal expansion of the experimental setup for the actual specimen deformation. The compensation scheme works well to validate the analytical formulations for a similar setup based on codal provisions. The development and numerical validation of the compensation scheme was carried out using python to form the basis for experimental evaluations.