Failure Modes of Two-Pile Caps Evaluated with Consideration for Uncertainties in Geometrical and Mechanical Properties and the Additional Impacts of Corrosion

Pile-caps are reinforced concrete (RC) members used to transmit and distribute loads from the superstructure to the foundation. They are often used in groups for the support of bridges, buildings, and offshore structures. Although design codes provide various formulations of safety indexes, the combined effects of external loading and corrosion have received limited attention in the literature. This paper presents a probabilistic study of the failure modes of two-pile caps, combining reliability analyses with chloride diffusion and corrosion scenarios for a specific structural configuration. Several analytical analyses, also using specific software developed by authors, accounting for the variability of geometries, materials and loadings have been carried out. In particular two key nodes in cap (cap-column and cap-pile) are studied following the strut-and-tie model (STM). Results show that bending failure is the most critical failure mode, that specific geometrical parameters play a crucial role in structural safety, and that corrosion may significantly accelerate the increase in failure probability under the adopted simplified scenario. The results are valuable not only for research but also for practical engineering applications, as they help clarify the most influential variables and support more consistent interpretations of failure scenarios under uncertainty.