Seismic Retrofit of Reinforced Concrete Beam-Column Joints with CFRP Composites

This is an experimental study on a new seismic retrofitting method of a longitudinally over reinforced reinforced concrete beam-column joints. The objective of the retrofit is to increase the story shear capacity with externally placed CFRP composite to ensure a strength of beam-yielding mechanism by shifting the critical part from the joints to the beam ends. Four one third scale reinforced concrete interior beam-column joint subassembleges were constructed and subjected to statically cyclic lateral loading simulating earthquake. The main parameter of the test is with and without a retrofit. Externally placed CFRP composite for seismic retrofit of beam-column joints has been considered as challenging because the presence of transverse beams and floor slab limit the accessibility to the joint in actual three-dimensional frame. The method in this study overcomes the difficulty by placing only four CFRP bundled strands vertically at the four corners of a column. Due to its simplicity it is applicable to most types of three dimensional beam-column joints with transverse beams and floor slab despite of architectural restrictions. Test result shows that a joint shear failure was altered to a beam-hinging mechanism and the story shear increased to the shear at flexural capacity of beams. It is verified that the new retrofitting method is one of the practical solutions for seismic retrofits of critical beam-column joints.