Mechanical anchorage system in retrofitting of RC slabs using CFRP rods and concrete jacket

Abstract

Over the past few decades, the demand for retrofitting reinforced concrete members has risen dramatically. Retrofitting reinforced concrete slabs with carbon-fiber-reinforced polymer (CFRP) rods and ultra-high-performance-fiber-reinforced-concrete (UHPFRC) jackets is the one of significantly effective techniques. However, the main challenge of employing CFRP rods and UHPFRC jackets technique to strengthen existing reinforced concrete members is the efficiency of using CFRP rods and the debonding issue between old and fresh new concrete jacketing. Debonding mostly occurs between CFRP rods and old concrete, as well as the surfaces of old and new concrete, and is especially prevalent when the slab is subjected to daily repetitive loads such as cyclic loads. In this study, a new retrofitting system utilizing a mechanical anchor system was proposed to improve the bond between the UHPFRC layer and existing slab. This mechanical system incorporates an expandable anchorage bolt and steel plates. Therefore, a benchmark RC slab and two retrofitted RC slabs were experimentally tested under a five-point incremental repeated load (cyclic load) employing the dynamic actuator. The influence of embedded CFRP rods into the jacket of UHPFRC on the performance of system were studied. The experimental results showed that the newly proposed approach was significantly effective in preventing early debonding. In addition, the mechanical system played an essential role by improving the attachment between the jacket and the slab, ensuring better load transfer. A new proposed retrofitting technique improved the capacity of slabs from 164 to 298kN, illustrating an improvement of over 82%. On the other hand, the FE models have been developed to provide both practical validation and deeper analytical insights, ensuring a comprehensive evaluation of the proposed retrofitting system. Experimental data were used to validate the results of the finite-element models, which showed good agreement and high accuracy. Finally, a parametric study was executed to evaluate the impact of various parameters on the performance and efficacy of the new suggested strengthening technique, and to optimize the proposed system parameters, including the diameter of bolts, a normal strength concrete (NSC) jacket with various grades rather than the UHPFRC, applying the proposed retrofitting technique on a compressive side instead of a tension zone, and rebar steel of varying diameters in the jacket instead of CFRP rods. Findings indicated (parametric study) that using anchor bolts with a diameter greater than 12 mm improved the slabs’ ultimate load capacity.