Analytical and numerical models to determine the strength of RC exterior beam–column joints retrofitted with UHPFRC

Analytical and numerical models are proposed to assess the strength of exterior Reinforced Concrete (RC) Beam–Column Joints (BCJs) retrofitted with Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) jacket subjected to cyclic lateral loads. In particular, an analytical flexural model is provided to calculate the flexural strength of the beam converging to the BCJ. The flexural model is also used to determine the shear force acting in the joint at beam flexural failure. An analytical shear model to calculate the joints' shear strength is also proposed. This model considers the contributions to the joint strength of both the joint core and the UHPFRC jacket and takes also into account the confinement effect produced by the jacket on the joint core. The flexural and shear analytical models are validated through the comparison with experimental results available in the literature, showing high accuracy in the predictions. The finite element model of a BCJ retrofitted with HPFRC jacket for which experimental test results are available in the literature is also implemented. A solution to reproduce the interface interaction at the contact surface between concrete and UHPFRC is proposed. The numerical model shows good accuracy in predicting the joint experimental behavior.