Effect of concrete slab on the behavior of fire exposed subframe assemblies with bolted double angle connections

This paper presents the development of a three-dimensional nonlinear finite element model for evaluating the system-level transient fire response of double angle connections that are part of a sub framed assembly. The behavior of two subframe assemblies, with double angle connections, exposed to different fire scenarios were modeled using a commercially available finite element software ANSYS. The finite element model accounts for material and geometrical nonlinearities, degradation of constitutive material properties with temperature and non-linear contact interactions. The model is validated by comparing predicted thermal and structural response parameters of connection assemblies with measured data from fire tests on subframe assemblies with and without the concrete slab. The validated model is applied to study the effect of decay rate, loading type, presence of the concrete slab and degree of axial restraint on the fire performance of double angle connection assemblies. Results from the parametric studies indicate that decay rate, loading type and axial restraint have significant influence on the transient fire performance of subframe assembly. Further, presence of the concrete slab significantly enhances the rigidity of the connection assembly and mitigates local instabilities, such as local and lateral torsional buckling, that arise in beams and this improves the performance of connections.