Evaluation of Corner Crack Widths in Dapped-End Connections and Knee Beam-Column Joints

The main vulnerability of dapped-end connections is the formation of a dominant inclined crack at the re-entrant corner of the connection. Such cracks are difficult to control as they open significantly before the formation of secondary cracks. For this reason, the crack width cannot be evaluated based on conventional methods assum-ing a stable crack pattern of multiple parallel cracks. Similar dominant corner cracks also occur in knee beam-column joints under opening moments. The opening of the corner crack causes serviceability and durability issues, as corrosive agents can pen-etrate through the crack. The long-term result is reduced main reinforcement and de-teriorated bond between the bars and concrete. Therefore, it is critical for the design of dapped-end connections and joints to accurately evaluate the width of the corner cracks and to ensure their control.
To address this need, the current study proposes a novel mechanical model for sim-ple and accurate crack calculations. In a first step, the model predicts the opening of the corner crack at the yielding of the connection/joint. In a second step, the model is developed to capture the complete load versus crack width response, where the load is expressed as a fraction of the failure load. The shape of the response reflects the effect of secondary cracking, as well as the effect of restrained shrinkage at low loads. The paper presents the formulation of the model and its validation with tests.