Seismic retrofit of short RC coupling beams using CFRP composites

To improve the deformation and energy dissipation capacities of conventionally reinforced coupling beams with low shear span to beam depth ratios, a new method for seismic retrofitting coupling beams using carbon-fibre-reinforced polymer (CFRP) composites is proposed and studied. Experiments are conducted to test four large-scale coupling beams with identical geometries and reinforcement layouts but with different retrofitting schemes. The effects of the arrangement of CFRP sheets and CFRP anchors on the seismic behaviour in terms of strength, stiffness, ductility, energy dissipation capacity and failure modes are evaluated. The study indicates the proposed retrofitting technique is well suited to improving the seismic behaviour of low-slenderness coupling beams in moderate seismic zones. The use of CFRP U-wraps can significantly improve the deformation and cumulative energy dissipation capacities of coupling beams while the beam stiffness can remain nearly constant. By using diagonal CFRP sheets, the strength, stiffness and energy dissipation capacity of coupling beams can be increased. The delamination of CFRP U-wraps can be delayed by using CFRP anchors, but sufficient insertion depth of the anchors is required to avoid their pull-out failure.