Application of X-Shaped CFRP Ropes for Structural Upgrading of Reinforced Concrete Beam–Column Joints under Cyclic Loading–Experimental Study

Abstract

The effectiveness of externally applied fiber-reinforced polymer (FRP) ropes made of carbon fibers in X-shape formation and in both sides of the joint area of reinforced concrete (RC) beam–column connections is experimentally investigated. Six full-scale exterior RC beam–column joint specimens are tested under reverse cyclic deformation. Three of them have been strengthened using carbon FRP (CFRP) ropes that have been placed diagonally in the joint as additional, near surface-mounted reinforcements against shear. Full hysteretic curves, maximum applied load capacity, damage modes, stiffness and energy dissipation values per each loading step are presented and compared. Test results indicated that joint sub assemblages with X-shaped CFRP ropes exhibited improved hysteretic behavior and ameliorated performance with respect to the reference specimens. The effectiveness and the easy-to-apply character of the presented strengthening technique is also discussed.

A Review of Fibre Reinforced Polymer Structures

“…CFRP ropes have been used as a strengthening method to improve strength, stiffness and seismic response of reinforced concrete beam-to-column joints in a recent paper [71]. The authors used X-shaped CFRP ropes to strengthen both sides of exterior beam-column joints.…”

“…CFRP ropes significantly increased strength and seismic performance of the joints. The cracking in strengthened specimens did not appear CFRP ropes have been used as a strengthening method to improve strength, stiffness and seismic response of reinforced concrete beam-to-column joints in a recent paper [71]. The authors used X-shaped CFRP ropes to strengthen both sides of exterior beam-column joints.…”

Behavior of RC Beam–Column Joints Strengthened with Modified Reinforcement Techniques

“…Hence, the investigation and research in the field is beneficial, and new methods, techniques, and procedures can help achieve a better understanding of the complex behavior of the joints themselves. Strengthening and upgrading such elements can be completed, e.g., by high-strength steel bars [39], steel jacketing [40], cementitious composites [41], FRP ropes [42], self-centering friction haunches [43], etc. The RC beam-column joints can also be predicted by using modern techniques such as machine learning [44].…”

Analytical Model for the Design of HSFC and UHSFC Jackets with Various Steel Fiber Volume Fraction Ratios for the Retrofitting of RC Beam-Column Joints

“…In this equation, for values of x + ψ ≤ 0.55, which correspond to aspect ratio values lower than 2.0 (as in real practice), the value (x + ψ) 5 in Equation ( 15) is quite small (x + ψ) 5 ≤ 0.051 = 5% and can be ignored without affecting the curve morphology. Therefore, the curve of the concrete biaxial strength for the part BC can be simplified and substituted by a line equation (Equation ( 20)) (see Figure 7), which is used to calculate the ultimate shear capacity of the joint region, τ ult .…”

“…Earthquake events of the last sixty years worldwide revealed numerous weaknesses of reinforced concrete (RC) structures built in the 1950s-1970s period or previously [1][2][3][4][5][6]. The devastating social and economic impact caused by catastrophic collapses triggered the reformation and refinement of the building codes, while also clearly demonstrating the immense need for retrofitting of the existing RC structures.…”