FRP retrofit for RC frame substructures against progressive collapse: Scheme optimisation and resistance calculation

Fibre-reinforced polymer (FRP) strips have been widely used to retrofit existing reinforced concrete (RC) frame structures to improve their progressive collapse resistance. However, existing FRP retrofitting schemes improve structural collapse resistance by simultaneously enhancing the tensile and flexural strengths of horizontal structural members. The enhancement in flexural strength may lead to an unfavourable strong-beam weakcolumn mechanism in the seismic scenario. Hence, existing FRP retrofitting schemes were optimised in this study by numerical investigation using LS-DYNA, and effective schemes against both progressive collapse and earthquake were identified for RC beam-column and beam-slab-column substructures. The identified schemes remarkably improved the structural performance against progressive collapse at large deformations whilst marginally affecting the progressive collapse resistance at small deformations to guarantee the strong-column weak-beam mechanism in the seismic scenario. Furthermore, based on the parametric analyses for 81 fullscale substructures, analytical methods were proposed to calculate the strength of RC frame substructures retrofitted with the identified schemes under catenary mechanism, which can be further used to design the FRP retrofitted RC frames.