Transverse　tests　of　two　ordinary　reinforced　concrete　(RC)　beams　and　eight　partially　prestressed　concrete　(PPC)　beams　strengthened　with　U-shaped　steel　plates　were　carried　out　under　static　loads　to　investigate　the　influence　of　the　damage　degree,　thickness　and　height　of　steel　plates,　magnitude　of　effective　prestress　and　loading　mode　on　the　flexural　performance　of　the　PPC　beams　strengthened　with　U-shaped　steel　plates.　Numerical　analysis　was　also　made.　Conclusions　are　drawn　as　follows:　The　cracking　development　can　be　effectively　restrained　using　the　proposed　method　of　strengthening　with　U-shaped　steel　plates,　and　the　flexural　load-carrying　capacity　of　the　normal　section　of　the　strengthened　PPC　beams　can　be　effectively　improved;　compared　with　the　PPC　beams　without　damages　before　strengthening,　the　yield　load　and　stiffness　of　the　PPC　beams　with　damages　before　strengthening　are　reduced　to　varying　degrees;　the　level　of　initial　effective　prestress　mainly　affects　the　flexural　behavior　of　the　beams　in　the　service　stage;　the　nonlinear　finite　element　(FE)　model　can　be　used　to　predict　the　flexural　performance　of　the　strengthened　PPC　beams,　and　the　results　well　agree　with　the　test　results;　in　practice,　it　is　suggested　that　the　height　of　the　bonded　steel　plates　on　both　sides　of　the　beams　should　not　exceed　one-third　of　the　height　of　the　beams.