Axial Cyclic Behavior of FRP Confined Seawater Sea-Sand Concrete Piles

Fiber-reinforced polymer (FRP) composites coupled with seawater sea-sand concrete (SSC) provide an innovative and sustainable solution by replacing the conventional piling materials for the marine infrastructure. This study investigates the axial behavior of FRP composite SSC model piles subjected to cyclic loading of different amplitudes and mean load levels. The strain along the depth of piles is measured by an advanced distributed optic sensing technique called optical frequency domain reflectometry (OFDR) having a spatial resolution of 1 mm and ±1με sensing accuracy. Three structural configurations, FRP tube confined and FRP rebars cage reinforced and centered FRP rebar SSC piles ended in rock-socket, are investigated in physical models to examine the performance of FRP composites and SSC in pile foundations. The accumulated displacement of model piles under different modes of axial cyclic loading are analyzed and explored in detail. It is found that the accumulation of permanent cyclic displacement increases markedly initially till 30 cycles and then followed a constant trend with increasing cycles passing. Under the same cyclic loading conditions, the FRP tube confined model piles exhibited lower cyclic degradation leading to stable behavior. The FRP tube confined model piles showed higher confinement and axial cyclic capacities compared to those reinforced with FRP rebars. The OFDR sensing technique monitored the localized effects efficiently that how the load is distributed along the length of model piles.