The importance and use of vertical crack displacements for the assessment of existing reinforced concrete deep beams

The accurate assessment of cracked reinforced concrete structures is becoming increasingly more important as the world's infrastructure ages and resources for retrofit and replacement remain limited. While existing approaches can be used to predict crack information for comparisons with on-site observations, there remains a need to establish methods that use crack measurements as a direct input to assess residual structural capacity. Critical wide cracks have been observed in lightly reinforced deep beams leading to questions about the safety of concrete bridges. To assess such deep members, this paper answers three important questions: 1) which critical crack displacements should be measured?; 2) where should the critical crack displacements be measured?; and 3) what is the residual shear capacity of the member, given the measured critical crack displacements? To answer these questions, detailed data from large-scale experiments is examined and interpreted with the two-parameter kinematic theory (2PKT). The results illustrate the importance of vertical crack displacements for conducting assessments of lightly reinforced deep beams. The paper shows that when the measured crack shape is incorporated into the 2PKT, the residual capacity of deep beams can be determined from measured critical crack displacements.