Strengthening a steel bridge with CFRP composites

Abstract

The present paper reports the successful strengthening of Acton Bridge on the London Underground system using carbon fibre reinforced polymer (CFRP) plates. The adhesive used to bond the plates to the steel had to cure while trains continued to run over the bridge. Concerns arising from this were the effect of cyclic load during curing on the final bond strength and whether adhesive flexibility affected the reinforced section properties. Tests to investigate these concerns are also reported. These tests involved reinforced beams subjected to cyclic loading of different intensities in bending during adhesive cure and tested statically at intervals to determine the build up of stiffness. The tests showed that, generally, adequate bond develops but at higher load intensities the strength of the bond is reduced and above limiting values of slip or developed shear stress at the steel/CFRP interface no bond will develop. A further conclusion was that adhesive flexibility does reduce section properties but by less than about 7%. Lap-shear tests conducted on specimens cut from the reinforced beams confirmed the bending test results. These showed that the biggest reductions in bond strength were at the ends of the beams where slip and shear stress were greatest.