Effect of lateral confinement on concrete fatigue life under shear loading

Abstract

In several recent mesoscale and macroscale material model formulations, the authors hypothesized that fatigue evolution in the material structure can be realistically modeled by defining a cumulative measure of inelastic shear strain as the fatigue driving mechanism. The standard method of fatigue characterization using cylinder compression tests induces shear only as a secondary effect within the volume of the specimen. To validate the hypothesis that fatigue at subcritical load levels is determined by a cumulative measure of inelastic shear strain, experimental methods with dominant shear strain appear more appropriate. In the present work, the punch-through shear test (PTST) setup is used to induce shear-dominated strain within the volume of the specimen. Furthermore, the ability to control and measure lateral confinement is utilized. An experimental study of the fatigue behavior of a high-strength concrete is presented, in which the influence of different degrees of confinement on the fatigue life of the concrete at subcritical load levels is evaluated. The study analyzes the accelerating or retarding effect of confinement on the development of fatigue damage that occurs as a result of compressive normal stress. To enable an efficient and realistic representation of the pressure-sensitive, shear dominated fatigue response, an axisymmetric idealization of the PTST test is proposed, modeling the shear ligament using the fatigue microplane model MS1. In this model, the tangential damage at the microplane is linked to a cumulative inelastic strain to reflect the accumulation of fatigue damage owing to internal shear/sliding between aggregates at subcritical load levels. The model aims to capture the basic inelastic mechanisms that are driving the tri-axial stress redistribution within the material zone during the fatigue damage process in concrete.