Effect of discrepancy in thermal expansion coefficients of CFRP and steel under cold temperature

Abstract

High modulus carbon fiber reinforced polymer (CFRP) laminates are often used to strengthen steel plate girder bridges. In the case of environmental load, discrepancy in the coefficients of thermal expansion (CTE) between the steel and CFRP can generate interfacial stresses along the CFRP-bond line. Thermally-induced stresses may accelerate premature debonding of the CFRP, thereby decreasing the efficacy of CFRP-strengthening. The present study examines thermal deformation and the strength of CFRP–steel composite elements exposed to cold temperature. The experimental program investigates long-term deformation of a composite strip subjected to a sustained flexural load and structural performance of an H-beam strengthened with CFRP laminate under cyclic cold temperature variation. The experimental observations verify that the CFRP laminates are firmly bonded to the steel substrates (steel-strip and H-beam) even in the cold temperatures. It should be emphasized that premature debonding of the CFRP laminates was not observed in these severe environmental conditions. In addition, the flexural test confirms that thermal deformation due to the discrepancy is negligible in cold temperature of mild weather condition.