Since post-tensioned concrete is widely used in all types of buildings and civil works projects, the formwork designer and builder must understand how the post-tensioning will affect the selection and design of the shoring.
INFORMATION NEEDED TO PLAN THE SHORING
An important first step in determining the loads for shore design is to obtain certain information from the plans and specifications and when necessary from the engineer of record. Questions that must be answered include:
1. Which members are post-tensioned?
2. What are the design service live loads and dead loads?
3. Did the engineer use any allowable live load reductions in the structural design?
4. Are any members stage-stressed?
5. What are the tensioning sequence and the amount of tensioning at each stage of stressing?
Then the shoring must be analyzed at least twice, considering: the pouring loads; and the post-tensioning transfer loads.
OTHER DESIGN CONSIDERATIONS
The formwork designer should watch carefully for conditions that will require special attention. These include post-tensioned beams over thin-section slabs below, transfer girders that may not be tensioned until multiple levels of construction are complete, or transfer girders that are stage-stressed.