Rapid crack-based assessment of deep beams based on a single crack measurement

Deep beams in concrete infrastructure often exhibit wide diagonal shear cracks that extend from the supports to concentrated loads. A key problem in these cases is to assess the residual capacity against shear failure across such cracks. This problem can be solved by establishing a relationship between the opening of the crack and the residual capacity, expressed in percentage of the shear strength. The current study establishes such a relationship that requires minimal input information. The input consists of only three on-site measurements: the depth of the critical loading zone (CLZ) determined by the diagonal crack; the angle of the crack in the CLZ; and a single crack measurement: the vertical crack displacement in the vicinity of the CLZ. The physical basis of the proposed crack-based assessment (CBA) is established with the help of a targeted test and advanced modelling. It is shown that only three input parameters and two simple closed-form equations are sufficient to accurately evaluate the residual capacity of diagonally cracked deep beams with various properties. Furthermore, in the presence of loading and unloading cycles, the proposed CBA reveals how close the member has come to shear failure throughout its entire service life. These properties render the CBA not only suitable for rapid assessment, but also for long-term monitoring of deep beams with diagonal cracks.