Structural behaviour of reinforced concrete beams strengthened by epoxy bonded steel plates
The development of synthetic adhesives based on epoxy resins has opened new possibilities for bonding structural materials together. The present work was concerned with the use of epoxy resins to strengthen reinforced concrete beams by externally bonded steel plates. It was found in the first part that the assessment of the properties of the epoxy adhesive is of paramount importance as they varied considerably with the thickness of the test specimen and the rate of loading. The adhesive proved to offer a bond stronger than concrete in shear and resulted in a composite action between the beams and steel plates. Preloading the beams prior to strengthening them did not have any adverse effect on their behaviour. The added strength from the plates was fully exploited even in beams which were held under a preload of 70% of their ultimate strength while being strengthened. Stopping the plate in the shear span, short of the support, created a critical section where premature bond failure occurred beyond a certain plate thickness. Failure was caused by the combination of high peeling and bond stresses present in the region where the plate was stopped. These stresses were due to the transfer of tensile forces from the plate to the bars in that region and were higher with thicker plates. Bonding steel plates on the tension face of the beams increased their shear capacity by 9 to 15%. This may have been due to dowelling action from the plates which had a greater contact area with concrete than an equivalent amount of internal steel bars. The use of externally bonded steel as shear reinforcement was effective but requires further investigation. The external web strips failed prematurely as compared to equivalent stirrups. The long term deformations in plated beams were highly affected by the conditions of their environment but despite 47 month exposure no visual deterioration of the concrete-epoxy-steel joint was observed.