Spall Behaviors of Metaconcrete: 3D Meso-Scale Modelling

Spalling is a typical tensile fracture phenomenon due to insufficient tensile strength of concrete. Concrete structure might experience severe spall damage at the rear surface of the structure owing to reflected tensile stress wave induced by impulsive load. In recent years, metaconcrete consisting of engineered aggregates has attracted attentions as metaconcrete exhibits extraordinary wave-filtering characteristics. Metaconcrete can be used to attenuate stress wave generated by impulsive load and hence possibly mitigate the spall damage. In this study, engineered aggregate is designed via the software COMSOL to have the frequency bandgap coincide with the dominant frequency band of stress wave propagating in the normal concrete (NC) specimen to reduce the stress wave propagation and hence spall damage. The wave propagation behaviors in metaconcrete specimen with periodically distributed engineered aggregates have been investigated in a previous study. This study establishes 3D meso-scale model of metaconcrete including mortar, randomly distributed natural aggregates and engineered aggregates to simulate spall behaviors of metaconcrete via the software LS-DYNA. The responses of metaconcrete composed of engineered aggregates with single bandgap and multiple bandgaps are studied. The results show that stress wave can be more effectively attenuated by using engineered aggregates with multiple bandgaps. It is found that although engineered aggregates mitigate stress wave propagation, the soft coating of the engineered aggregates reduces the concrete material strength, therefore spall damage of metaconcrete specimen is not necessarily less severe than the normal concrete, but has different damage mode. In addition, the influences of loading intensity and duration on stress wave, as well as the spall behaviors of metaconcrete specimen are also studied.

Preliminary Experimental Study on the Influence of the Local Wind Field on Forces From Breaking Waves on a Circular Cylinder

The spatial localized influence of wind on wave induced load on a flexible cylinder has been assessed throughout a test series conducted in a wave-wind-current flume at Newcastle University. The tests are motivated from other experimental and numerical investigations showing air flow separation on the leeward side of steep waves that can lead to added wind energy transfer, which could suggest an increase in the impulsive wave loading. The waves are generated as focused waves, resulting in a plunging breaker, leading to an impulsive wave load. The test model was equipped with a load cell measuring the connection load. Due to the flexibility of the cylinder, the measured force response shows oscillations and dynamic amplification of the load. The maxima of the force responses are compared for the tests with and without wind. Another measure for comparison is the local and short-lived impulse, which is responsible for the amplification. This impulsive load is estimated from the load cell and acceleration measurements. For the tests in this study, the introduction of wind over the breaking waves does for some cases lead to a slight increase in the peak of the impulsive load and thereby the load response, although large scattering is present. Further investigations are needed to verify this effect. Some differences in the time series of the free surface elevation are observed when wind is present, but the maximum of the surface elevation does not change notably, and the slope is only minimally changed, meaning that this should not give basis for the differences in the loads.

Impact on an Ice Floe With a Surface Crack

A floating two-dimensional ice plate with a crack on its lower surface is considered. Deflection of the plate is caused by an external impulsive load. The ice floe dynamics is described by thin compound elastic plate equation. Two parts of the plate are of constant thickness and are connected by a torsional spring which models the crack effect on the elastic deflection of the plate. The stiffness of the equivalent torsional spring is given as a function of the plate parameters and the crack length. Both the motions of the ice plate and the stresses near the crack tip are determined without account for gravity and surface tension effects. In the symmetric problem, the crack is always perpendicular to the plate surface. The growth of the crack is governed by the condition of the crack equilibrium at each time instant. The conditions of the impact, the magnitude of the impact force and its duration, which lead to the crack growth are studied within the water impact theory.