Abstract
The use of the innovative material of Carbon Fiber-Reinforced (C-FRP) ropes as external near surface mounted reinforcement for the strengthening of reinforced concrete beam-column joints is studied. The ropes are diagonally applied forming external X-type reinforcements on both sides of the joint body. The efficiency of the technique is mainly based on the assumption that the confinement of the joint body due to the applied X-shaped ropes and the contribution of the ropes as shear reinforcement are efficient enough to reduce the shear deformations observed in the joint core during the seismic excitation. Thereof the experimental measurements of the shear deformations of nine full scale beam-column joints tested in cyclic deformations are elaborated and presented herein. The specimens are sorted in two groups. Specimens of group A have been designed in the way that damage is mainly expected in the beam. On the other hand, in order to investigate the efficacy of the use of the ropes for substandard joints the group B specimens have been designed in the way that cracks and some damages are expected to develop in the joint body. Systematic and extended comparative presentations for specimens with and without ropes proved in all the examined cases that the externally mounted C-FRP ropes kept the joint body intact and substantially reduced the shear deformations especially in high drifts. Moreover, the influence of the externally mounted X-shaped C-FRP ropes on the seismic behaviour of these specimens is also examined in terms of the developing principal tensile stresses inside the joint body. From the comparisons of the principal stresses developing in specimens with and without X-form C-FRP ropes it became quite obvious that the ropes kept the joint body intact and allowed the development of higher values of principal stresses comparing with the stresses developing in specimens without ropes.
Highlights
Research on the efficiency of strengthening techniques for reinforced concrete elements constitutes a scientific field of utmost importance due to the vital issue of the structures’ safety in seismic prone areas and due to the relevant huge financial interests. applied techniques for the strengthening of reinforced concrete joints aiming at reducing repair time have been recently reported [1]
From the comparative presentation (Table 2 and Figure 6) of the observed joint shear deformations of specimens JB1 and JB1Fx it can be observed that the X-form C-Fiber Reinforced Polymers (FRPs) cords substantially improved the behavior of the joint in specimen JB1Fx
The effectiveness of the innovative strengthening technique of beam-column joints with externally applied Carbon FiberReinforced Plastics (C-FRP) ropes is examined in terms of the developing shear deformations of the joint body and the study of the tensile principal stresses
Summary
Applied techniques for the strengthening of reinforced concrete joints aiming at reducing repair time have been recently reported [1]. New materials like Fiber Reinforced Polymers (FRPs) in the form of sheets or bars have been reported for the strengthening or rehabilitation of deficient or damaged reinforced concrete elements [1–11]. A review with an extensive database extracted from the literature about tested beam-column joints strengthened with FRPs are presented in a state-of-the-art report by Pohoryles et al [5]. Murad et al [6] proposed the application of FRP sheets for the rehabilitation of beam-column joints made of recycled concrete. An experimental investigation of the effectiveness of the use an innovative anchor for FRP sheets externally applied for the strengthening of beam-column joints has been experimentally investigated [8,9]. Strengthening techniques using steel products mounted on the surface of concrete elements have been reported [18–21].
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