Cyclic Behavior of FRP Strengthened Beam-Column Joints under Various Concrete Damage Levels

Abstract

This paper is intended to examine the efficiency of utilizing the FRP composite material with an externally bonded technique in enhancing the behavior of the damaged B-C joints and controlling their failure mode using the NLFEA approach. At first, the modeled Beam-Column joint was validated as per the previously-attained experimentally-attained results. Later, the model was widened to experiment with the impact of axial-column load and the concrete compressive strength on the reinforced and un-reinforced models with FRP. To run the experiment, there were three cases of applying the axial column load: no load applied (0%), applying 25%, applying 50%, and applying 75%, while the concrete compressive strength degradation level was (0% damage), (25% damage), and (50% damage). All models were evaluated for structural performance, considering: the failure mode, stresses distribution, and the ultimate capacities in pulling and pushing with its corresponding displacements. However, the horizontal load-displacement hysteretic loops and envelopes, stiffness degradation, displacement ductility, and energy dissipation were reported. The experimental results revealed that using FRP to externally-reinforce B-C joints improved overall cyclic performance, as the FRP caused a rise in the ultimate load capacity, horizontal displacement, ductility of displacement, and displacement energy dissipation, while it slowed down the stiffness degradation. In addition, the FRP material converted the failure mode of the region between the joint and column from brittle to ductile due to the formation of a plastic hinge only on the side of the beam when the axial column load exceeded 25%. It must be noticed that when the column’s axial load is less than 25%, the ultimate capacity of axial load and resultant deflection is solely improved. However, it has been stated that increasing the column’s axial loading by 25% increases the resulting stiffness degradation by 3% for undamaged joints, which further increases by 16% for each increased damage level. In contrast, the absorbed energy is increased by 170% under axial loading, increasing by 25%, which is reduced to only one-fourth under the various damage levels. Generally, the resulting observations help specialized engineers retrofit appropriate B-C joints in already-standing buildings due to their accuracy.