Numerical and analytical modeling of seismic behavior of beam-column joints retrofitted with ultra-high performance fiber reinforced concrete

Strengthening the seismic deficient beam-column joints (BCJs) in reinforced concrete structures is mostly adopted to avoid any devastating consequences of high-intensity earthquakes. To evaluate the performance of BCJs against seismic action, experimental testing of BCJs under cyclic loading is a time-consuming and cost-intensive work due to the requirement of large-scale instrumentation and testing. This paper reports a study on the numerical and analytical modeling of the seismic behavior of BCJs built using normal concrete and retrofitted with ultra-high performance fiber reinforced concrete (UHPFRC). A computer simulation using the nonlinear finite element (FE) method was developed considering a concrete damage approach in modeling both types of concrete, i.e., normal concrete (substrate) and UHPFRC (overlay). The interface between the substrate and overlay was modeled as a cohesive element. The properties of this bonding interaction were experimentally evaluated based on the results of the push-out test. The simulation results benchmarked with the experimental data of a previously published study. It was found that the proposed FE model is in good agreement with the experimental behavior of seismically tested specimens in terms of global load–displacement, ultimate load, and damage evolution. In addition, the use of surface-to-surface cohesive elements played an important role in the bonding interface under cyclic loading. Additionally, an analytical model was developed to predict the shear capacity after retrofitting the BCJ. The results obtained by using the analytical model were consistent with the corresponding experimental values. Finally, a parametric study was carried out to examine the effects of the thickness of UHPFRC jacketing and longitudinal reinforcements ratio of the beam on the performance of the retrofitted BCJs.