This paper identifies some of the parameters and design considerations for using external prestressing in prestressed concrete flexural members. The behavior and design of these members are differentiated from those prestressed with internal bonded tendons. The paper elaborates on such issues as bonded versus unbonded tendons, internal versus external tendons, the effects of friction and slippage at tendon deviators, the behavior of members with deviators at different locations, and various code issues. The paper also proposes a modification to the Nebraska University (NU) girder series that would reduce the web thickness of those girders by 3 in. (76 mm) (thus reducing their self-weight by 25 percent) and add external posttensioning. Finally, a bridge design example of a precast, prestressed girder implementing the proposed modification - combining pretensioned and external post-tensioned tendons - is provided. The design and analysis involve the use of a computer program, and the validity of the proposed method is verified by comparing the numerical results with published experimental data.
