Research on Mechanical Performance of Spatial Grid Structure Under Long-duration Fire Conditions Considering Creep Effect

The creep effect becomes significantly pronounced when a steel structure has prolonged exposure to fire. To investigate the influence of creep on displacement, stress, and fire resistance time of spatial grid structure subjected to fire, a square pyramid spatial grid structure was taken as the research object. The element tangent stiffness matrix considering creep effect was derived, and a series of numerical simulation models were established with two constitutive models of materials, a creep model and an elastoplastic model. A comparative analysis of whether to consider creep effects was performed, aiming to assess the differences in the structural response and fire resistance duration of the spatial grid structure subjected to fire. The analysis indicates that the creep effects on both displacement and stress can be disregarded for structural fire durations under 0.5 h, however, once the fire duration exceeds 0.5 h, structural deformation increases significantly, especially when the creep is considered, and the stresses in members decreased significantly, therefore, the influence of creep must be considered in the fire analysis of spatial grid structures to avoid unsafe predictions. The research results aim to provide valuable references for the analysis of spatial grid structure fire responses and post-fire assessments of structures.