Selective weakening techniques for retrofit of existing reinforced concrete structures
This paper presents the conceptual development and the preliminary analytical-experimental results of a counter-intuitive approach for the seismic retrofit and rehabilitation of older reinforced concrete buildings, referred to as selective weakening (SW). The basis of a SW strategy is to modify the inelastic mechanism towards a more desirable mechanism by first weakening selected regions of the structure for protection against brittle failure mechanism. Subsequently, if necessary, the structure is further upgraded to the desired strength/stiffness/ductility and energy dissipation capacity. Different levels of performance can be achieved, from collapse prevention to damage control. The feasibility of alternative techniques to implement a SW strategy is first conceptually discussed for structural walls, precast hollowcore floors and reinforced concrete frame systems. Focus is then given to the implementation of SW to the retrofit of exterior beam column (bc) joints with substandard details. The mechanics and effectiveness of partial SW of the beam within an exterior bc joint subassembly is numerically investigated using a 3D finite element micro-plane model. Finally, the global behaviour of a prototype frame prior and after a SW retrofit is investigated using non-linear time history analyses.