Structural effects of freeze-thaw depth on shear strength of an existing RC bridge pier

Frost damage develops unevenly inside concrete, adversely affecting the structural performance of existing RC structures. A recent study reported by Hayashida et al. (2014) revealed that RC beams subjected to freeze-thaw action exhibited unexpected shear failure under different degrees of damage depth. Although extensive research has been conducted to investigate freeze-thaw damage mechanisms, most such work has been limited to examination of small-scale specimens of plain concrete or mortar. Few practice-based approaches to assess the mechanical performance of large-scale RC members have been reported. Several works bridge the gap using finite element models coupled with poro-mechanics (Gong et al. 2018) and continuum damage mechanics (Berto et al. 2015). However, these are complex and challenging to implement for the assessment of existing deteriorated structures. In this respect, a simple physical model to predict shear strength is necessary for practical use. The shear strength of an existing RC bridge pier is assessed using the upper bound theorem in these analyses. The upper bound theorem in the plastic analysis requires equality between internal and external works and explicitly accounts for different shear transfer actions. Based on freeze-thaw depth obtained from on-site inspections, the analyzed piers are divided into undamaged and damaged zones. Their internal work is minimized with respect to the angles of inclination under an assumed displacement field. The shear strength is determined accordingly. The developed analysis showed that the current shear strength was 12 % less than that in the intact condition. Furthermore, reduction in shear strength under different levels of freeze-thaw depth is discussed in terms of shear resisting components.