Experimental and Numerical Investigation on Flexural Strengthening of Precast Concrete Corbel Connections with Fiber-Reinforced Plastic Sheet

This paper presents the results of experimental and numerical investigations aimed at enhancing the flexural capacity of Precast Concrete Corbel Beam-Column Connections (PC-CBCCs) using Fiber-Reinforced Plastic (FRP) sheets. The experimental study primarily focused on assessing the flexural capacity of pinned PC-CBCCs reinforced with FRP layers, comparing them to a moment-resisting connection. A series of half-scale specimens, including three PC-CBCCs with varying FRP configurations, were tested alongside one in situ concrete fixed connection. The first specimen (PC-1) utilized L-shaped and full-wrap FRPs, whereas PC-2 and PC-3 employed both U-shaped and full-wrap layers. The objective is to quantify the ultimate flexural capacity of PC-CBCCs reinforced by FRP sheets. In PC-3, the external anchorage is introduced to assess its influence on delaying the FRP layer debonding under lateral loading. The effects of the FRP layer thickness, locations, and potential debonding are examined under unidirectional static tests while applying a constant axial compressive load to the columns and subjecting the beams to lateral loads until fracture. The test results illustrate that strengthening the corbel connection with L-shaped FRP or spiral U-shaped FRP sheets without mechanical anchorage cannot result in a significant bending capacity due to debonding. However, with the incorporation of mechanical anchors, the connection manages to enhance the moment capacity to 81% of a fixed connection's flexural capacity. Additionally, a finite element model of the PC-CBCCs and a fixed joint is developed to simulate nonlinear static analyses of the connections using ANSYS 19.2 software. The simulation model is precise in predicting the initial stiffness and ultimate capacity of the beam-column joints, as verified by the experimental results. A comprehensive comparison is conducted to determine their responses by employing various FRP configurations and properties. Moreover, design parameters such as bond length and thickness of the FRP sheets, along with appropriate mechanical anchorage, are identified as effective in preventing debonding, and delamination. However, wrapping the beam far away from the joint interface has a minimal impact on the failure mode, stress reduction, and load-bearing capacity.