Analysis of Delamination of Post‐Tensioned Silos

Delamination of walls, where the outer concrete sloughs off, can occur in concrete post‐tensioned silos whose tendons are embedded in the silo wall rather than being placed around the outside of the curved wall. One potential source of this wall concrete failure is bending moment generated by kinks (due to improper splicing) in tendon ducts. This bending moment causes radial tensile stress concentrations. The writers have studied the problem analytically by the finite element method. Initial studies involved three‐dimensional (3‐D) models of the failed area with a linearly elastic material model. Subsequent studies use a two‐dimensional (2‐D) mesh and a nonlinear concrete material model that can account for compression crushing, tensile cracking, and aggregate interlock. Variation in kink angle and prestressing force are investigated. Tensile stresses of sufficient magnitude to initiate cracking failure of the concrete are discovered. Specific recommendations and construction details to minimize the occurrence of the problem are suggested.