Rehabilitation of seismically-damaged RC beam-column joints with UHPC and high-strength steel mesh reinforcement

Abstract

In the aftermath of strong earthquakes, diagonal shear failure in RC beam-column joints is a prevalent damage pattern observed in older buildings lacking seismic detailing. This research investigated the efficacy of ultra-high-performance concrete (UHPC) jackets reinforced with high-strength steel mesh for rehabilitating such seismically-damaged exterior beam-column joints. The primary aim was to determine if this novel repair approach could both restore and enhance the seismic performance of the compromised joints. The conclusions drawn from this study were based on systematic experimental evaluations of four beam-column joint specimens and were further supported by strength models, encompassing both the joint shear strength model and a fiber-based cross-sectional analysis. The findings revealed that the UHPC jacket, fortified by high-strength steel mesh, demonstrated an exceptional capability to curtail extensive joint diagonal cracks and column splitting cracks, which were characteristic of the original, substandard beam-column joint specimens. This remedial measure enabled the beam's flexural yielding to predominantly govern the cyclic behavior of the rehabilitated specimens. Notably, the joint shear failure evident in the original specimens was effectively prevented post-repair, resulting in a surge of up to 93 % in peak strength. Furthermore, the tension-stiffening behavior manifested by the steel mesh-reinforced UHPC emerged as a pivotal factor in the structural rehabilitation, influencing aspects such as damage patterns, load-displacement hysteretic responses, stiffness, energy dissipation capacity, steel mesh strain demands, and thresholds for repairable and collapse drift ratios. Complementing the experimental findings, this study proposed appropriate strength models, namely the joint shear strength model and the fiber-based cross-sectional model, to evaluate the failure modes of the rehabilitated beam-column joint components. These models successfully captured the joint shear and beam flexural behaviors observed in the experiments with reasonable accuracy. The findings suggest that the proposed UHPC jacketing, reinforced with high-strength steel mesh, along with its analytical model, offer effective and viable solutions for seismic rehabilitation practices. These methods not only restore but also significantly enhance the seismic performance of damaged beam-column joints.