Repair of cracked reinforced concrete beams with adhesive bonded steel plates

M.Ing. (Civil Engineering)Abstract: Concrete structures often suffer from cracking and deterioration caused by factors such as impact and dynamic loading, static overload and construction faults. This requires immediate repair to prevent further degradation and to restore structures integrity. Externally bonded steel plates are used to repair such damaged concrete structures in a number of projects in various parts of the World, but their overall performance is still not fully understood. The main objective of this study is to investigate the flexural behaviour of pre-cracked reinforced concrete beams, repaired by bonded steel plates on their soffit, using epoxy adhesives. This implied an experimental investigation, which took place in Material Laboratory of the Department of Civil Engineering Science at the University of Johannesburg. Twelve full-scale beams of 175 mm wide x 300 mm deep x 3200 mm long were pre-cracked, repaired with steel plates and tested to failure in flexure under a two-point loading. Two variables were included in this investigation, namely; plate size and loading conditions. The plate size was varied by changing its width, which ranged from 75 mm up to 175 mm, in increments of 25 mm and the beams were pre-cracking at serviceability load and at 85% of the maximum load. During the experiments, the following aspects were evaluated and recorded regarding the response of tested beams: flexural strength, stiffness, maximum deflections and failure modes. Externally bonding the steel plate to the pre-cracked reinforced concrete (RC) beams resulted in increased stiffnesses and maximum load capacities up to 153% and decreased in the maximum midspan deflections up to 38%. The strength and rigidity of the repaired beams were found to increase with increasing the width-to-thickness ratio of the steel plate from 12.5 to 29.17. The results also showed that bonded external steel plate can only enhance the maximum load capacity of the repaired beams to a limited extent. There exists a limit in the width-to-thickness ratio for which the load can increase. The experimental results showed that the structural integrity of the repaired beam not only can it be restored but also enhanced. The bonded external plate contributed more to the control of maximum load capacities than to the control of deflections