Bond behavior and assessment of design ultimate bond stress of normal and high strength concrete

The aim of this work is to assess the ultimate bond stress of normal and high strength concrete. This study contains two phases. The first phase included the studied bond behavior using two different models. In the first model, single pull-out test (SPOT), the concrete section of specimen was subjected to compressive stresses. In the second model, double pull-out test (DPOT), the concrete section of specimen was subjected to tensile stresses. So this phase of study aimed to make a comparison between the single pull-out test and the double pull-out test. To compare the behavior of these models, different levels of compressive strength were considered through the use of different coarse aggregate types, different W/C ratios and different cement contents. The second phase focused on the study of bond strength of high strength concrete using double pull-out test to assess design ultimate bond stress. In this phase, the effect of concrete compressive strength, bar diameter, concrete cover, embedded length, and pre-flexural crack length was studied. Based on the test results, a proposed concept to assess design ultimate stress of normal and high strength concrete was adopted. Equations to calculate the design ultimate bond stress, and required development length were suggested.