Validation of an Alternative Reinforcing Detail for the Dapped Ends of Prestressed Double Tees

P. C. Huang and A. Nanni

Center for Infrastructure Engineering Studies, University of Missouri-Rolla 224, Engineering Research Laboratory Rolla, MO 65409-0710

Prestressed concrete dapped-end beams have been used in buildings and parking structures as they provide an efficient and economical construction system. The reentrant corner of a dapped-end beam develops a severe stress concentration, which makes it the weakest point of the connection. If suitable reinforcement is not provided at this location, diagonal tension cracks may propagate rapidly and failure may occur with little or no warning. Reinforcing schemes and associated methods of design, which combine simplicity of application with economy of fabrication and provide the margin of safety required by present building codes, have been developed.

In recent decades, precast prestressed concrete structures have become more and more prevalent in the construction industry. The use of prestressed concrete has been shown to be technically advantageous, economically competitive, and esthetically superior because of the reduction of cross-sectional dimension and consequent weight savings, enlargement of span length, cracking and deflection control, and larger shear force resistance. The use of precast concrete can improve the quality of the final product, decrease construction time and assist the progress of construction in adverse weather conditions. Unlike a cast-in-place reinforced concrete structure that is by its nature monolithic and continuous, a precast concrete structure is composed of individual prefabricated members that are connected by different types of joints. The type of connection used determines the behavior of a precast structure under load.

The design of dapped-end connections is one of the important considerations in a precast prestressed concrete structure even though its analysis is complex. The shape of the dapped-end develops a severe stress concentration at the reentrant corner such that the conventional flexural theory is only partially applicable. In addition to the calculated forces from external loads, dapped-ends are also sensitive to horizontal tension forces arising from restraint of shrinkage or creep shortening of the member.

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