Title: Simple Design of Partially Post-Tensioned Silos and Other
Concrete Structures under Combined Tension and
Author(s): German Gurfinkel
Publication: Structural Journal
Appears on pages(s): 508-516
Keywords: cracking; delamination; hoop tension; hoop bending moment;
iteration; post-tensioned concrete; radial reinforcement; reinforced con-crete;
Large silos and tension chords of transfer trusses are subjected to the combined effects of tension and bending moment. These structures may be partially post-tensioned to reduce the required amount of conventional reinforcement and improve behavior under service loads. Strength design requires that load-factored tensions and moments be contained within the confines of the reduced tension-moment branch of the ultimate interaction diagram of the section. A simple method that can be used for both design and review of these structures is given. Thus, two linear equations are established that accurately represent the reduced tension branch. The required areas for both post-tensioned and conventional steel may be easily obtained from these equations. Two design examples, including a silo struc-ture and a tension chord of a transfer truss, are given to illustrate the method. Finally, a caveat is issued on potential delamination of silo walls resulting from radial tensions caused by post-tensioning, and hoop moments generated while emptying the silo contents. A formu-la is given to design steel ties placed radially across the thickness of the wall.