Selective weakening and post-tensioning for retrofit of non-ductile R.C. exterior beam-column joints

A counter-intuitive “selective weakening” (SW) seismic retrofit strategy for non-ductile RC frame is presented. By focusing on increasing the global displacement and ductility capacity, simple retrofit interventions such as selective weakening of the beams and external post-tensioning of the beam-column joints could change the local inelastic mechanism and result in improved global lateral and energy dissipation capacities. After an overview of the SW retrofit concept, this paper presents the experimental and numerical investigations of SW retrofit techniques for non-ductile RC exterior joints. The experimental results of nine 2/3-scaled exterior joint subassemblies– as-built and SW retrofitted tests are briefly presented. Parameters considered in the tests included the presence of column lap-splice, slab and transverse beams, level of post-tensioning forces and location of beam weakening. Numerical investigation using 3D micro-plane concrete model within smeared fracture mechanics finite-element modelling is demonstrated for SW retrofitted joints. Lastly, a preliminary design procedure is outlined for the design of SW retrofit for exterior beam-column joints. With its economical, non-invasive and low-technology intensity approach, SW retrofit has potential for a wide implementation