Real-time hybrid simulation to capture column buckling in steel frames under fire

Real-time hybrid simulation can be used to test physical models of a structural element or a sub-assembly with actuators applying loading and realistic boundary conditions in real time, considering interaction with the rest of the structure. When applied to structural fire engineering, this approach enables cost-effective fire experiments as compared to full-scale structural fire tests. This paper describes the application of a control strategy for real-time hybrid fire simulation that decouples the physical substructure response from the control design. The mathematical formulation of the proposed strategy is presented as an example of a steel moment frame with one column under fire. The steel column first experiences slow thermal expansion under elevated temperatures, followed by dynamic buckling at failure. The proposed real-time hybrid fire simulation strategy is tested using a shear-slip mechanism where a bolt serves as a locking element within a sliding shaft to emulate the considered steel column. At the start of the test, the bolt takes the force applied by an actuator that moves slowly to mimic thermal expansion. The bolt eventually shears, and the sliding mechanism displaces quickly to mimic buckling. A servo-hydraulic actuator, tuned to replicate the behaviour of the surrounding frame, communicates the interfacing boundary condition. The test is able to capture slow thermal expansion and the dynamic behaviour at the time of buckling, for which the obtained result is also applicable to progressive collapse applications in general.