Design and Behavior of Dapped-End Beams

T dapped-end beam is a useful concept. It enables the construction depth of a precast concrete floor or roof structure to be reduced, by recessing the supporting corbels into the depth of the beams supported. In a "cantilever and suspended span" type of structure, the suspended span is a dapped-end beam, and the ends of the supporting cantilevers are similar to the ends of the dapped-end beams, but inverted. The use of dapped-end beams facilitates the erection of a precast concrete structure, due to the greater lateral stability of an isolated dapped-end beam than that of an isolated beam supported at its bottom face. Despite the fairly extensive use made of this form of construction, few studies 1' 2 appear to have been made of its behavior. These were primarily analytical, utilizing the finite element method to analyze the stresses in and around the dapped end under service load conditions. From these analyses, Werner and Dilger2 were able to predict the shear at which diagonal tension cracking would occur at the re-entrant corner. They also proposed that the shear strength of the dapped end could be calculated using: