Concept and implementation of a selective weakening approach for the seismic retrofit of RC buildings
Current seismic retrofit strategies generally focus on increasing the strength/stiffness or upgrading mechanical properties of a structure. A typical drawback with this is that the upgraded behaviour might result in an increased demand on the structural and sub-structural elements, i.e. foundation. Herein proposed is a counterintuitive but rational seismic retrofit strategy of selectively weakening a structural system. Such a retrofit strategy is suitable for application to alternative seismic resisting systems and components including walls, beams, columns and diaphragm connections. A selective weakening intervention is performed within an overall performance-based retrofit approach with the aim of improving the inelastic behaviour by first reducing the strength/stiffness of specific members within the structural system. This in turn results in a reduced demand on the structural member. Once weakening has been achieved the designer can use the wide range of techniques and materials available (e.g. use of fibre reinforced polymers, steel plates, jacketing or shotcrete) to ensure that adequate characteristics are achieved. Whilst performing this it has to be assured that the structure meets specific performance criteria and the principles of capacity design. As the first phase in the development of selective weakening, the feasibility of such a retrofit strategy is discussed, with particular focus on possible applications to the seismic retrofit of existing reinforced concrete structural walls. The proposed intervention involves splitting the wall vertically and cutting it at the foundation level to change the inelastic mechanism from shear-type to a flexural/rocking-type behaviour. As part of the overall research program, a series of experimental (quasi-static cyclic) tests on 2/3 scaled reinforced concrete walls representing pre-1970 construction practice or retrofitted configurations are under preparation. A summary of the retrofit strategy design and expected behaviour will be herein given.