Responses of steel casing composite piles of bridges under impact loads

Impact-induced damage to piles threatens bridge safety. Hence, the impact behaviour of a widely employed type of steel casing composite (SCC) pile needs to be investigated. To improve the understanding of the impact behaviours of SCC piles, pendulum impact tests were conducted on 21 specimens. The effects of the steel casing length, impact mass and velocity, and superstructure mass on the impact responses and failure mode of the piles were systematically investigated. In the absence of the upper mass (during the construction stage of bridges), piles with the optimum steel casing length sustained flexural failure within the wrapped region, whereas the short steel casing led to a more concentrated and brittle failure of the uncased concrete near the casing bottom. Furthermore, with an increase in the impact velocity, failures of piles with short steel casings transferred from bending to bending-shear. However, in the presence of the upper mass (during the service stage), piles with the optimum casing length failed in the cap-pile joint owing to high inertia. By revealing the failure behaviour of SCC piles under different impact conditions, the present study provides insight into the impact design and damage evaluation of SCC piles in practice.