An empirical approach to simulate the concrete softening mechanism.

Abstract

Material properties of concrete play an important role in the analysis of reinforced concrete RC members. One of the most commonly used material properties is the compressive stress strain σ-ε relationship. Uniaxial compression tests on concrete cylinders are used to obtain these material properties of concrete in compression. These tests are effective up to peak stress, but have limited applicability post-peak stress, primarily due to the influence of size. These cause the absence of an accurate material softening stress-strain relationship. Hence, the post-peak softening behavior of a reinforced concrete member is not been able to be simulated accurately since there is not an accurate softening σ-ε relationship for concrete. An alternative approach is required. Recently, shear friction theory has been used to simulate the softening behavior of concrete. Shear friction theory quantifies the relationship between the shear stress, normal stress, displacement and separation of the softening concrete in relation to the adjacent (non softening) concrete. In this thesis, an approach is presented to extract the shear-friction softening properties of concrete from experimental tests on long concrete prisms. Empirical mathematical expressions are developed which quantify the relationship between the softening stress and the displacement of the softening wedge. These empirical stress-displacement expressions are then applied to the analysis of eccentrically loaded concrete prisms. The theoretical analyses of these eccentrically loaded prisms agree well with the experimental results, indicating the applicability of using this approach to extract the softening shear-friction properties of concrete, from prism tests, and subsequently using these empirical expressions to simulate the post peak response of concrete.