Post tensioned tendons

Structural Details: In this building, the post-tensioned (PT) tendons act similar to beams running through the concrete slab. When the tension is removed from the cables of the PT tendons are locked-off, the result is similar to the floor losing its support beams. The typical solution to this situation is to place shoring under the affected areas to replace the support. However, in this case, shoring to support the adjacent bays would interfere with the tenants' business operations.

Our Approach: Because of the project constraints, it is possible only if at some place shoring directly under the slab opening, not under adjacent slabs, as that would result to less capacity similarly the cables were de-tensioned. This required the design team to create a phasing plan in which they determined which cables were allowed to be de-tensioned and in which order. This lock-off phasing plan allowed the crews to de-tension individual PT tendons, while maintaining the structural integrity of the entire floor system. The project was phased in small sections in order to minimize disruption to the existing businesses and most of the work was performed at night. Once the tendons were re-tensioned, the crews would begin the concrete demolition for the next lock-off phase. The total square footage of the project area was 3,600 square feet.