Experimental study on shear behavior and size effect of high strength lightweight aggregate concrete deep flexural members

To avoid the potentially dangers caused by size discrepancies between actual structure and scaled model, a total of 15 lightweight aggregate concrete (LWAC) deep flexural members with section height of 500-1 400 mm and shear span-effective depth ratio of 0.85-1.73, was tested to study the size effect, failure mechanism, shear bearing capacity and design method. The shear behavior, including failure process, failure modes, load-deflection curves, loads at characteristic points, reinforcement strains and inclined crack propagation, were systematically analyzed. The accuracy and applicability of strut-and-tie model-based code provisions and shear models for specimens were verified. The test results indicate that there are two different failure modes, namely, shear-compression failure and diagonal splitting failure, which are independent of beam section sizes. With the increase in section height from 500 mm to 1 400 mm, significant size effect on normalized ultimate shear stress is manifested with an approximately 37% decrease. Instead, the increasing shear span-effective depth ratio leads to an appreciable reduction in both the normalized cracking and ultimate shear stresses. Calculation results show that, the GB 50010-2010'Code for design of concrete structures' without reasonable consideration of size effect on the strength of LWAC leads to conservative results. The predictions obtained from EC2, ACI 318, Tan-Cheng and Tang-Tan models show good agreement to the test results. It is suggested that a rational effective struts coefficient shall be considered when using CSA code. © 2020, Editorial Office of Journal of Building Structures. All right reserved.