Fracture mechanics of a verticel-wall struetuve and the predicting wodel

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A series of experimental programs has been performed to study the physics of dynamic behaviors of an elastic vertical wall to impulsive forces due to breaking waves. On basis of the experiments, the author discussed severe local fractures of the vertical-wall type structure, and intended to develop a model for evaluating the wave impact force which brings about the failure.The elastic wall exhibits different behaviors according to the colliding or loading condition of breaking waves on the wall. The wall does not respond to the high impact pressure with short duration, because such high pressure generated at a very limited area in the vicinity of the still water level. In general, a lower impact pressure is associated with a lagerpressure impulse. Consequently, the longer-lasting low impact force associated with damping force oscillations is more effective in producing the larger wall deflection than the single-peaked impact. In addition, the largest wall deflection occurs when the rise time of the impact is almost the same to the natural period of wall oscillations.Collisions of plunging breakers usually entrap a large air pocket at impact and produce damped force oscillations after impact. Such loading condition of the impact force brings about a higher probability of fatigue fracture to the wall member of the structure. On the other hand, a sharp impact pressure with very high magnitude and short duration occurs a shear fracture around the still water level on the wall. The resulting damage would develop and may cause a sudden failure of the structure.To develop the impact pressure model, variability in the impact processes of breaking waves on the wall is examined with respect to the force impulse per unit width of the wall, the entrapped air volume, and so forth. Numerical analyzes using an finite element method were made to substantiate the experimental results and the impact force model.