Four-Phase Composite Material of Concrete Meso-Damage Dynamic Load Failure Test

Abstract

At mesoscopic scale, the research proposed and established that concrete was a four-phase continuous and inhomogeneous composite material model consisting of coarse/fine aggregates, hydration products in cement, pores, and cracks. Under static and dynamic loads, micro-mechanics damage test simulation was based on the four-phase composite material model of concrete. The research’s content was concrete uniaxial compression test, three-point bending girder’s damage, and fracture under static and dynamic loads. The research found that the location of main crack in the beam shear was near the frailest part. The crack was along the bone and sand slurry’s combination, extending to the loading point direction and showing tortuosity. The crack extended surface was uneven, which was temporary deflection of the crack propagation direction due to the heterogeneity of concrete and aggregate distribution in it. The stress–strain curves of static and dynamic loads were similar, and the starting points of fracture initiation were basically identical. The stress wave in the specimen propagated back and forth many times, which led to the specimen fracture. Under the dynamic load, the elastic modulus of concrete was higher than that under the static load, and the numerical simulation results agreed with the experimental results. When the strain rate was less than a critical value, concrete strength increased slowly. When the strain rate was more than the value, concrete strength increased quickly. This research established five-layer, eight-layer, and 10-layer concrete frame structural models, which were simulated at the damage process of frame structure in strong earthquake. The study found that beam and column alternating failure belongs to the mixed collapse mechanism. The weaker the stiffness of foundation was, the earlier the failure time of lower floors was and the deeper the structural settlement was. The stronger the stiffness of foundation was, the earlier the failure point generated. The low floor failure of frame structure consumed a part of seismic energy, which reduced the effect of earthquake on upper frame structure partly.