Numerical analysis on collapse performance of post-tensioned concrete frames with post-tensioning BFRP bars under an interior-column-removal scenario

Basalt fiber reinforced polymer (BFRP) bars are ideal substitutes for steel reinforcement due to their excellent mechanical performance, which could avoid energy consumption and carbon dioxide emission during the production of construction steel. Concrete structures reinforced with BFRP bars encounter the collapse risk under an occasional accident, such as losing one or several load-bearing members. To date, little research has been performed on the collapse behavior of post-tensioned concrete frames with bonded post-tensioning BFRP bars. This paper developed finite element (FE) models of frame substructures with post-tensioning BFRP bars to investigate their collapse behavior under an interior-column-removal scenario. Parametric analyses show that arranging post-tensioning BFRP bars at the top and bottom of the frame beams or increasing the post-tensioning BFRP bars at the beam bottom could effectively improve the collapse resistance and deformability of the substructures, with the 96.6% and 51.9% improvement at the most, respectively. Reducing initial effective prestress is helpful to the deformability of the frame beams, resulting in a 56.9% increase in ultimate vertical deformation. A mixed reinforcement of BFRP bars and steel reinforcing rebars in the beams is beneficial in preventing collapse. In most cases, the beams’ flexural mechanism and catenary action are essential in resisting the collapse load. The ratio of the maximum vertical displacement at the failed interior column to the net span of the frame beam varies between 0.051 and 0.1. The calculation model for equivalent dynamic increase factors (DIFs) of collapse load was proposed, which could provide a reference for determining DIFs when static collapse analysis is conducted. The DIFs of collapse load for the substructure models were discussed in the proposed method based on the analytical results, indicating that DIFs approached 2.0 at the initial collapse stage and varied between 1.26 and 1.70 at the final collapse failure.