Real-time hybrid fire testing of a steel column

Graduate Student: Ramla K. Qureshi

Principal Investigator: Negar Elhami-Khorasani

Collaborators: Mettupalayam Sivaselvan, Scot Weinreber

Project Completion Date: 2/1/2021

Real-time hybrid simulation, or dynamic substructuring, is an innovative technology only recently introduced to the domain of structural fire testing, where it promises more realistic response evaluation as opposed to currently available element-level “standard” fire tests. Typically, this technique couples physical and computational sub-models of a structural system to emulate static and dynamic interactions at the boundary that may be present during a fire scenario. The physical substructure (denoted as PS) is a laboratory test specimen, and the numerical substructure (or NS) is a finite element computational model of the remaining structure. Servo-hydraulic actuators operating in feedback control function as “active boundaries”, and are used to apply interfacing force-displacement conditions to the PS. The corresponding response is measured and then fed back to the NS, providing a continuously updating response history throughout the duration of the fire test in real-time.

This project researched a control strategy for real-time hybrid fire simulation, where a transfer system (TS), consisting of a servo-hydraulic actuator and a controller, was designed to mimic the behaviour of the NS independent of the physical substructure PS. The mathematical formulation for the behaviour of the NS, parametric identification of a servo-hydraulic actuator, and their integration to arrive at a controller model were developed for an example case of an example of a steel moment frame with one column under fire. For sake of repeatability, it was opted not to use a structural steel column with heating elements in the lab. Instead, a shear-slip mechanism was used, where a bolt serves as a locking element within a sliding shaft. The locking mechanism is designed to take increasing loads (implicating small displacements as expected in the case of thermal expansion) until the bolt breaks, and the sliding mechanism displaces quickly; mimicking the behaviour of PS column in the frame that experiences compression until buckling. The real-time hybrid fire simulation algorithm was able to capture the expected behaviour of a steel column when it buckles, i.e., a dynamic failure, by going through a free-vibration with a matching frequency as the NS, once failure occurred. The expected thermal expansion of the steel column could be captured by lowering span of the actuator.

This project was partly supported by the American Association of University Women (AAUW) International Doctoral Fellowship. The project was also partly supported by the University at Buffalo MDRF grant.