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The technique of strengthening concrete structures by bonding steel plates to the external faces, using epoxy adhesive, was pioneered in the late 1960s. It has been used extensively in the UK since 1975 when the M5 Quinton Interchange was strengthened. Most applications have been to increase flexural strength or stiffness by bonding plates to the soffits or top surfaces of beams and slabs.
Work in the laboratory has shown that the shear strength can be increased by bonding plates to the side faces of structural elements.
Plates are generally mild steel and at least 4 mm thick to prevent distortion during the preparation process. The maximum practical plate length is 6 metres. Bolts are required at the ends of plates to prevent local high shear and normal stresses causing peeling failure.
Acknowledgement: The Concrete Society
Other references:Highways Agency, ´Strengthening of concrete highway bridges using externally bonded plates´, BA 30/94.