Risk-based overall seismic robustness assessment of cold-formed steel structures considering vulnerability and fragility

Structural robustness assessment is a hot topic in the field of civil engineering. Although many robustness researches have been conducted on hot-rolled steel, reinforced concrete and timber structures, very few investigations have been reported for cold-formed steel (CFS) structures. This paper proposes a novel risk-based seismic robustness assessment methodology for CFS structures based on vulnerability and fragility, where the consequence and the probability are evaluated by structural vulnerability analyses and seismic fragility analyses, respectively. This insight was used for assessing the conditional seismic robustness (CSR) of CFS structures to predefined local damage events. This paper aims to propose the concept of overall seismic robustness (OSR), where the assumption that the occurrence probability of the local damage event is 1 in CSR is abandoned, and some typical damage states are used as the local damage events instead of the predefined ones. A 5-story CFS shaking table test model is selected as a benchmark model, and this paper quantifies the OSR of the models with different sheathing materials. The results show that: the model with better ductility exhibits a higher OSR, which is the same finding as the finding by Baker et al., indicating the validity of the proposed methodology. The methodology could not only considers the changes in failure consequence and probabilities, various uncertainties and occurrence probability of earthquakes in the service life of structures, but also considers the effects of structural repair, retrofitting and other factors. More importantly, the methodology could be conveniently used in engineering practice. Thus it would be a good choice for structural robustness assessment.