Nonlinear material modelling for fibre-based progressive collapse analysis of RC framed buildings

The choice of the most suitable constitutive models for fibre-based progressive collapse analysis of reinforced concrete (RC) structures is still an open issue, mainly because nonlinear material modelling has never been treated as a variable involved in the assessment problem so far. To support analysts in selecting which models could be more representative of the actual inelastic material response for progressive collapse analysis of RC framed buildings, this paper presents a numerical investigation where fibre modelling was integrated with different combinations of stress-strain relationships for concrete and reinforcing steel. A series of pushdown simulations of a two-bay perimeter frame mock-up were then carried out to assess the gravity load capacity under downward displacement. Analysis results are compared with available experimental test data for performance quantification of numerical models, which is based upon an experimental-to-numerical load capacity ratio and overall statistical parameters. Sensitivity to the material modelling approach, load eccentricity and boundary conditions is evaluated, involving strain indicators that can be used in performance-based robustness assessment of RC framed buildings. Finally, a number of parametric analyses are presented to show how the load capacity is influenced by capacity model properties, such as material strengths, beam span length, and span length ratio of asymmetric frames.