Coastal Engineering Journal

Parametric analysis of hollow precast prestressed piles indicated that under certain conditions of loading and geometry, plastic hinge formation could be expected in the pile shaft below ground level. Four half-scale model precast prestressed piles were tested in flexure to characterize plastic hinge development. The test rig simulated the subgrade moment pattern found in an in situ pile, and simulated external confinement from the soil around the pile shaft. Parameters varied were transverse reinforcement ratio, presence of external confinement, and presence of nonprestressed longitudinal steel in the plastic hinge region. The model piles were found to be insensitive to parameter variation. Failure occurred at similar levels of structural displacement in all cases, and in all cases took the form of compression failure of the pile wall. The piles had limited ductility, less than μ_Δ = 4 in all cases.

Laboratory experiments were conducted under sinusoidal sheetflow conditions. By using image analysis, which overcame the demerits introduced by intrusive measurements, the time-varying as well as maximum erosion depths for different flow conditions were estimated. The temporal variation of suspended sand concentration in the sheetflow layer showed high concentration during the deceleration phase and relatively low concentration during the acceleration phase. Rapid sand deposition was observed around flow reversals. The phase lag between the free stream velocity and the sand concentration increased with elevation. The temporal and the spatial distribution of suspended sand concentration revealed an asymmetry in the suspension process, namely relatively long suspension (erosion) and short sedimentation (deposition) reflecting the asymmetry in turbulence. The instantaneous sand particle velocities were estimated using a PIV technique. The mean particle horizontal velocity was found to decrease at the beginning of the acceleration phase, corresponding to the rapid deposition of sand.

Wave impact on one and two structural beams with rectangular cross section is simulated with a two-dimensional finite volume method, solving the unsteady Euler equations and employing a VOF-type method for the description of the free surface. Four different test series are carried out, each corresponding to a wave impact scenario in the experimental database of Sterndorff [2002]. For the case of wave impact on a single structural element the numerical results show good agreement with measured force time histories. In the computations featuring two beams, the prediction of the shadowing effect of the first beam on the second is in reasonable agreement with the experimental data. However, the force peak on the second beam is somewhat over-predicted. The calculations successfully predict a second peak in the force time series of the second beam, which is caused by airborne water shipped over the first beam. Throughout the work, spurious spikes of very short duration appear in the computed load time series, originating from the changing of the flow separation location along the lower edge of the beams.