Pulled to force P, the tendon exerts a uniform uplift ( PT) shown in part (b). The tendon shown in part (a) is in the shape of a simple parabola in each span. Contribution of post-tensioning in the reduction of the effect of dead load on the member.įigure 1 illustrates the concept in its basic form. The understanding and treatment of the hyperstatic effects is generally an obstacle for many structural engineers.įigure 1.
The computation and inclusion of the hyperstatic moments are necessary for the safety compliance of the member. The load-balancing method relies on the common knowledge and daily practice of consulting engineers except for the recognition and explicit computation of hyperstatic moments from post-tensioning. The load-balancing method did away with the complexity of post-tensioning design, which hindered its widespread adoption by structural engineers. Lin in the early 1960s and extended to non-prismatic members by the author, has led to increased application of post-tensioning in building construction. Load Balancingīasic load balancing, introduced by T. The straight method relies on the knowledge and tools that structural engineers commonly use, instead of the unique, rigorous method. For these applications, the straight method is preferred. In this case, the optimization of the post-tensioned members will have little impact on the overall economy of the project. It is not uncommon that a designer may have to verify the adequacy of a post-tensioned member or design of a couple of the members of the project with post-tensioning. It applies where more reliable deformation, cracking, and post-cracking information of the member are sought.
It provides a closer picture of the member’s response to post-tensioning, as opposed to merely meeting the code-specified requirements of serviceability and safety. Engineers who do not routinely design post-tensioning tend to pass the design to those specialized in the field. While simple and intuitive, it requires the computation of hyperstatic (secondary) moments – a somewhat unfamiliar concept for many engineers. Most post-tensioned concrete buildings are designed using the load-balancing method. The additional time and effort expended when using this method are offset by the economy in design. The application of each method depends on the extent of the project, the expectations of the client, and the expertise of the design engineer.Įngineers who specialize in post-tensioning design and who are comfortable with large and complex projects benefit most from the rigorous method. They differ substantially, however, both in the computational effort and potentially in the economy of the final design. All three methods, when followed correctly, result in serviceable and safe members. There are three fundamentally different methods to design a post-tensioned concrete member: load balancing, rigorous, and straight.
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