Effect of Thermal Distress on Residual Behavior of CFRP-Strengthened Steel Beams Including Periodic Unbonded Zones

Abstract

This paper presents the residual behavior of wide-flange steel beams strengthened with high-modulus carbon fiber-reinforced polymer (CFRP) laminates subjected to thermal loading. Because the coefficients of thermal expansion of the steel and the CFRP are different, temperature-induced distress may take place along their interface. Periodic unbonded zones are considered to represent local interfacial damage. Five test categories are designed depending on the size of the unbonded zones from 10 to 50 mm, and corresponding beams are loaded until failure occurs after exposing to a cyclic temperature range of ∆T = 25˝C (´10 to 15˝C) up to 84 days. The composite action between the CFRP and the steel substrate is preserved until yielding of the beams happens, regardless of the thermal cycling and periodic unbonded zones. The initiation and progression of CFRP debonding become apparent as the beams are further loaded, particularly at geometric discontinuities in the vicinity of the unbonded zones along the interface. A simple analytical model is employed to predict the interfacial stress of the strengthened beams. A threshold temperature difference of ∆T = 30˝C is estimated for the initiation and progression of CFRP debonding. Multiple debonding-progression stages in conjunction with the extent of thermal distress appear to exist. It is recommended that high-modulus CFRP be restrictively used for strengthening steel members potentially exposed to a wide temperature variation range.

Durability of the liquid rubber‐modified CFRP‐steel interface under freeze–thaw cycles

“…21 However, the CFRP/ adhesive and steel/adhesive interface and the adhesives itself generally degraded because of the moisture diffusion and temperature changes under freeze-thaw cycles. [24][25][26][27][28][29][30] There is no doubt that the freeze-thaw environment aggravates the premature debonding of the CFRP plate from the steel substrate. Recently, some possible solutions were studied to enhance the performance of FRP-steel interface by researchers.…”

“…In the CFRP externally bonded steel system, the CFRP composites have shown excellent resistance to freeze–thaw environment 21 . However, the CFRP/adhesive and steel/adhesive interface and the adhesives itself generally degraded because of the moisture diffusion and temperature changes under freeze–thaw cycles 24–30 . There is no doubt that the freeze–thaw environment aggravates the premature debonding of the CFRP plate from the steel substrate.…”