The innovative shear strengthening method using externally bonded CFRP reinforcement to strengthen prestressed concrete I-girders has been investigated in this thesis. These girders potentially have insufficient shear capacity because of the combination of thin webs and insufficient shear reinforcement. Shear failure of these girders should be prevented because they do not warn before the element fails in shear. Shear strengthening using externally bonded CFRP reinforcement seems promising because of low installation costs, negligible increase in weight, no decrease of clear height underneath the bridge and minimising the hinderance. The aim of this thesis is to investigate the feasibility of shear strengthening prestressed concrete I-girders using externally bonded CFRP reinforcement. The shear behaviour of prestressed concrete I-girders strengthened using externally bonded CFRP reinforcement has been investigated with the nonlinear finite element analysis (NLFEA) software DIANA. A three-dimensional finite element model of a 1.0 m high prestressed concrete I-girder with a kinked tendon profile and no shear reinforcement has been made to investigate several parameters and aspects of the CFRP reinforcement. Shear strengthening of prestressed concrete I-girders with vertical CFRP sheets and CFRP anchors is a feasible strengthening method because of the demonstrated potential increase in shear capacity. The externally bonded CFRP reinforcement was especially effective to increase the flexural shear capacity of prestressed concrete I-girders. The numerical analysis showed a promising increase in flexural shear capacity between 40-55% and an increase in ductility of more than 80% compared to the I-girder without CFRP reinforcement