Seismic retrofit of external RC beam-column joints by joint enlargement using prestressed steel angles

Reinforced concrete (RC) structures that were built prior to the 1970s generally do not meet current seismic design requirements, especially in terms of reinforcement details. An innovative and practical seismic retrofit method is proposed for non-seismically detailed external beam-column joints of existing concrete structures, based on a two-dimensional enlargement of the beam-column joint using steel angles that are mounted using prestressed cross-ties. Seven half-scale external RC beam-column joints were subjected to lateral cyclic loading of increasing amplitudes. The tested specimens comprised of three control units and four retrofitted units. The test results confirmed that the proposed retrofit method not only resulted in relocation of beam plastic hinges to outside the joint panel zone but also improved the bond between the longitudinal beam and column tension reinforcement and concrete in the joint panel zone. The proposed method was shown to significantly enhance the seismic capacity of the joints, in terms of strength, stiffness, energy dissipation and ductility capacity.