Bond behaviour between H-shaped steel and concrete after freeze-thaw cycles

By conducting push-out tests, the bond behavior between H-shaped steel and concrete under different freeze-thaw (F-T) cycles (including failure modes, bond strength, and bond stress-slip curves) was investigated. The experiment considered one type of concrete (C35), three volumetric stirrup ratios (0.4%, 0.8%, and 1.2%), and three F-T levels (0, 25, and 50 cycles). Based on the experimental results, the effects of F-T cycles and stirrup ratio on the bond performance were systematically analyzed. The results showed that prior to F-T exposure, specimens with a stirrup ratio of 0.8% and an anchorage length of 380 mm / 560 mm exhibited splitting failure, while specimens with a stirrup ratio of 0.4% and an anchorage length of 380 mm experienced pull-out failure. As the number of F-T cycles increased, the failure mode shifted from splitting failure to push-out failure. After 50 F-T cycles, the bond strength of specimens with 380 mm and 560 mm anchorage lengths decreased to 82.2% and 84.7%, respectively, compared to the unexposed condition. Under the same F-T conditions, the pull-out force and bond strength of specimens with a 1.2% stirrup ratio were higher than those with 0.4%. The bond stress-slip curve shape remained generally consistent before and after F-T cycles, but the peak stress decreased and the slip at the peak load increased with more cycles. A regression model was also developed to describe bond strength degradation, providing a basis for predicting long-term performance. These findings clarify the deterioration pattern of steel-concrete bond under F-T conditions and offer a technical reference for the safety and durability assessment of composite structures in cold regions.