Bond-slip model considering freeze-thaw damage effect of concrete and its application

The bonding behavior between concrete and steel bar may be severely deteriorated due to freeze-thaw damage of concrete, which may significantly affect the seismic performance of the reinforced concrete structures. This paper presents a novel bond-slip model considering freeze-thaw damage effect of concrete and apply it into the fiber model. The proposed model is developed by modifying an existing bond-slip model to consider the freeze-thaw damage effect of the concrete. The freeze-thaw damage effect of the concrete on the bond behavior is considered to be caused by the deterioration of both material strength and cover confinement of the concrete. The reliability and accuracy of the proposed model in capturing the freeze-thaw damage effect of the concrete on the bond stress-slip relationship are verified by comparison with pull-out tests data and existing models. Then, the steel stress-slip model is derived from the proposed bond-slip model based on the infinitesimal procedure. The derived steel stress-slip model is implemented into a fiber model that considers the freeze-thaw induced uneven damage along the member section. The general framework for applying the proposed model to a fiber beam-column element model is established. The proposed fiber model is validated by the experimental results and existing fiber model without incorporating the bond-slip effect. Excellent accuracy is observed between the model results and the experimental results. The fiber model without incorporating the bond-slip effect may overestimate the seismic performance of the freeze-thaw damaged reinforced concrete column. The results confirm that the proposed fiber model can comprehensively incorporate the degradation of uneven material strength and the deterioration of the bond behavior due to freeze-thaw damage effect of concrete.