Experimental study on the structural behavior of concrete dapped-end beams

• We tested four dapped beam ends under service and ultimate design loads.
• Three beam specimens included modifications for reducing diagonal cracking at the reentrant corner.
• In none the specimens the crack at the reentrant corner exceeded maximum allowed width under service load.
• Longitudinal post-tensioning of the dapped end significantly improved the performance in terms of diagonal cracking.
• The PCI Design Handbook conservatively predicted the load capacity of the specimens.

A common structural system in precast pre-stressed concrete girders with dapped ends has been intensively used in elevated viaducts recently built in Mexico City. A critical aspect of this solution resides in the possibility of a premature cracking in the reentrant corner of the dapped-end beam. An experimental research program was carried out to evaluate the performance of the present solution of the dapped end, both under service loading and ultimate design loads, and also to explore other solutions that could improve the performance in terms of the cracking of the reentrant corner.Four dapped-end beams models at a 1:3.6 scale were built and tested under vertical loads. The first specimen reproduced the solution adopted in the prototype, which was designed and reinforced according to the recommendations of the PCI Design Handbook. To the second one a longitudinal post-tension was applied, in the third specimen diagonal bars replaced part of the hangers, and the fourth was provided with both diagonal bars and post-tensioning.Experimental results allowed to conclude that, the specimens with longitudinal post-tensioning at the dapped, performed within the code requirements both under the service and ultimate loads, showed the best behavior in terms of cracking control. The strut-and-tie model proposed by Mattock provides a good prediction of the load capacity attained in the experimental specimens.