Multi-scale bolt connection model for thermo-mechanical simulations

A multi-scale simulation approach is proposed to predict the fire resistance of structures comprising connections by bolts, as a supplement to an existing two-way coupled CFD-FEM method. In the existing model, fire is modelled by CFD, and its effects on the overall structure are found via thermodynamic and thermomechanical models. In this paper, detailed thermomechanical models are presented to predict the behaviour of a bolt connection, in order to find the equivalent linear elastic stiffness for the bolt connection that is modelled as a spring in the overall structure. Each load step, the stiffness of the spring is determined by the detailed model, which for a certain temperature, boundary conditions, and load type, predicts the connection behaviour, including geometric and material non-linearity and failure. It will be shown that the detailed model simulates existing experiments for elevated temperatures well, and is able to predict all possible failure modes as listed in the Eurocode for ambient temperatures. It is then demonstrated that the model can also be used for all these failure modes for elevated temperatures. In the near future, a strategy will be developed to include the detailed models in the overall structure, within the two-way coupled CFD-FEM method.