Direct Crack-Based Assessment Approach for Shear Critical Reinforced Concrete Deep Beams

The main indicator of damage in aging concrete infrastructure are wide cracks. However, while the geometry and opening of the cracks can be measured with great accuracy using modern sensing technologies, this information is not used in a direct manner to evaluate the safety of cracked structural members. At the same time, tests of non-slender members such as deep pier cap beams in bridges have shown that variations in the geometry of the critical shear cracks can have a very significant influence on the shear resistance, and therefore on the safety of the member. This paper therefore presents a framework for the direct crack-based assessment of deep beams that can be used to rationally evaluate applied loads and level of structural safety. The employed assessment strategy is based on detailed measurements of the geometry and width of the critical shear crack. This information is used as input into the two-parameter kinematic theory (2PKT) for deep beams. The 2PKT is built on the kinematics of the critical crack, which are combined with equilibrium conditions and constitutive relationships for the shear resistance mechanisms across the crack to predict the complete shear response of deep beams. The 2PKT is capable of capturing flexural, shear and bar pull-out deformations. Using this approach, the shear response of deep beams from the literature is assessed and the results are compared to the experimentally observed load-displacement response, shear resistance, and crack widths. The comparisons demonstrate that crack-based models can be effective in assessing shear critical deep members in a rational manner.