Currently many bridges are considered inadequate for the current traffic loads due to various problems including rapid increases in the traffic volume and vehicle loads; exposure to adverse environmental conditions and structural aging. These bridges require either weight restriction, strengthening or even total re-placement. Strengthening of such bridges is cost-effective for bridge engineers rather than total replacement. External post-tensioning is considered as one of the effective methods to strengthen bridge structures. Unlike flexural strengthening, the shear strengthening of existing structures using external post-tensioning has not been investigated adequately. The existing shear cracks may have substantial effect in shear strengthening of structural members using conventional external post-tensioning. Even most of the current design codes do not have provision for the existing shear cracks (except some guidelines recommend these cracks should be re-paired prior to strengthening). This paper presents an experimental investigation on the effect of the existing shear cracks in such members strengthened with external post-tensioning.