Simplified energy-based robustness assessment for steel-composite car parks under vehicle fire

Due to a considerable number of reported car park fire accidents over the last few decades, robustness of these structures against localised fire is receiving increasing attention. Although a detailed analysis including fire modelling, heat-transfer analysis, and structural analysis may lead to a sound evaluation of structural robustness, it is too computationally demanding in practical design. In this respect, this paper proposes a simplified energy-based robustness assessment approach, namely, a Temperature-Independent Approach (TIA), in the sense that the maximum temperature is assumed to be unknown, thus adopting a similar basis to typical robustness provisions where event-independent local damage scenarios are employed. The new approach is inspired by the idea of 'sudden column loss' which is typically employed for blast loading, but is modified to enable its applicability to localised fire scenarios. Through considering degraded fire affected floor performance and energy balance during column buckling, the dynamic ductility demand after column buckling can be estimated from static ambient analysis. Through comparisons against the ductility supply, which is governed by the elasto-plastic joint response, the structural robustness can be assessed. Through comparisons with more sophisticated elevated temperature analysis, this simplified approach is shown to be both reliable and conservative.