In this study, the strengthening mechanism for the shear capacity of web plate by CFRP has been investigated. Loading tests were carried out with the several sheet bond direction as parameters. The mechanism was examined by the viewpoints of shear buckling strength and post-buckling strength. The carbon fiber sheet along the tensile axis of diagonal tension field can improve the post-buckling strength due to the retardation of yield occurrence at the tension field. On the other hand, both the shear buckling strength and the post-buckling strength increase by using the sheet along the compression axis, since the outof-plane deformation of web plate is prevented.
