Journal of Earthquake Engineering Vol. 2, No. 4 (1998) 525–568 c  Imperial College Press REPAIR AND RETROFITTING OF RC WALLS USING SELECTIVE TECHNIQUES A. S. ELNASHAI and R. PINHO Engineering Seismology and Earthquake Engineering Section, Imperial College Imperial College Road, London SW7 2BU, UK Received 16 December 1997 Revised 26 January 1998 Accepted 2 February 1998 In the context of capacity design philosophy, where a desired failure mode exhibiting adequate levels of energy absorption capacity is envisaged, control must be exercised on the member behaviour to safeguard the achievement of the target overall response. Therefore, local repair and retrofitting methods that result in unquantifiable effects on seismic response characteristics should be re-assessed. In contrast, techniques to affect, in a controlled and easy-to-monitor fashion, individual design response parameters, i.e. stiffness, strength and ductility, may provide a new framework for repair and retrofitting earthquake-damaged structures to mirror ‘capacity design’ principles used for new struc- tures. Such an approach is discussed in this paper and possible scenarios where selective intervention may be required are identified. A number of tests on RC walls are also reviewed to confirm the feasibility of the proposed intervention techniques. Finally, ex- tensive parametric studies are carried out, using verified analytical models, leading to the derivation of selective re-design expressions and guidelines. Keywords : selective, repair, retrofitting, walls, capacity re-design, RC structures 1. Introduction Conventionally, the philosophy behind repair/retrofitting schemes has been one of over-strengthening. However, in the light of modern ‘capacity design’ concepts used in seismic codes in which a significant role is assumed by the control of the overall response of RC structures, such an approach can be counter-productive. Structures designed to conform to a particular failure mode rely heavily on individual design response parameters of its members, such as stiffness and strength in shear and flexure, as well as ductility. Accordingly, repair or retrofitting methods which will affect these characteristics should consider not only the local but also the global effects of the intervention. In fact, local over-strengthening of individual members may cause stiffness irregularities or disturb the sequence of plastic hinge formation, thus jeopardising the whole retrofitting process. Moreover, several recent studies [Moehle, 1992; Calvi and Pavese, 1995; Kowal- sky et al., 1995] have introduced the concept of ‘displacement-based design’ as a 525