CONCRETE DELAYED FAILURE TIME

Abstract

At a single action on a concrete and reinforced concrete structure short-term dynamic load, the value of which may exceed the value of the static load-bearing capacity of the structure, it was observed that failure will occur not immediately, but after a certain time (delayed failure time td). If the dynamic load action is stopped before the moment td, the structure will not collapse. Therefore, the accurate determination of the delayed failure time of concrete is an important and relevant problem. To solve this problem, the paper presents a visco-elastic-plastic model to describe the stress-strain state of concrete under dynamic loading. This model consists of 2 elements: a nonlinear spring A and a piston B connected in parallel. Element A describes the nonlinear elastic-plastic properties of concrete, and element B takes into account the high-strain-rate effect of concrete. Under the action of sudden dynamic loads with an intensity greater than the static bearing capacity of the concrete, piston B helps to inhibit the development of deformations initiated in element A. Based on the proposed model, the delayed failure time is defined by the time interval required for the deformation of concrete to reach its ultimate value. The main factors affecting the deformation and failure of concrete such as concrete compressive strength, overload level, and viscosity are also investigated. Specifically, as follows: The higher the static compressive strength of concrete, the lower the delayed failure time. When a dynamic force of greater intensity is applied compared to the bearing capacity of the concrete, the faster the specimen will destroy. In addition, the viscosity coefficient significantly reduces the strain rate of concrete and the corresponding delayed failure time increases as the viscosity increases.