Investigation of the flexural properties of reinforced concrete beams strengthened by externally bonded steel plates
It is sometimes necessary to strengthen in situ concrete structures. Externally bonded plate reinforcement has been successfully applied to structures with subsequent satisfactory performance. However, little research has been reported, especially in respect to long term behaviour. The present study investigated the flexural behaviour of normal under- reinforced concrete beams with plate reinforcement bonded to their tensile face. Furthermore, long term studies of loaded and unloaded plated beams were initiated for testing after exposure to natural weathering conditions. The parameters under investigation were adhesive and steel plate thickness, the degree of cracking in the beam prior to bonding on the plates, multiple plate layers and plate jointing techniques. Test results showed that although the increase in ultimate load produced by the bonded plates was only 17%, the service loads were increased up to 90%. The deformations at service loads were reduced up to 65%. In general, the deformations decreased for an increase in adhesive or plate thickness, the latter having the larger effect. The maximum crack widths in the plated beams-were up to 63% lower than those in the unplated beam. The ACI and CP 110 crack width prediction formulae overestimated the measured values. Within the limitations of the present test series, empirical formulae were derived for calculating rotations, crack widths, crack spacings and concrete surface strains. Tests on specimens after 18 months weathering showed no loss of flexural performance nor any visual deterioration of the adhesive or adhesive/steel interface. Further tests will be reported. Bonded plate reinforcement can only enhance the ultimate strength of a beam to limited extent. More important are the decrease in deformations and consequently the increase in service loads, thus making it a viable technique for up-rating the load carrying capacity of existing structures.