Post-tensioning application part 2
post-tensioning is not limited to bridges or building superstructure. post-tensioning can be used in substructures. the following summarizes post-tensioning application:
- Transverse post-tensioning for top slab: transverse post-tensioning is often used for cast-in-place and precast top slab. tendons anchored in block-out at the edge of top slab cantilever wing. after stressing tendons are grouted and block-out is covered with a concrete and concrete barrier. Transverse post-tensioning can be used also to connect wide bridges made of twin box. twin parallel box is joined longitudinally using transverse post-tensioning.
- Transverse post-tensioning for diaphragm: sometimes diaphragm post-tensioned transversely. multi-tendons are used to post-tension a diaphragm. these tendons will extend from the face of one web to the face of another web as shown in figure no:2. post-tensioning diaphragm transversely will contribute to transverse tensile force capacity of the diaphragm. great attention shall be given for details of post-tensioning to ensure the system works properly and effectively as planned.
- Vertical post-tensioning for diaphragm: vertical post-tensioning in diaphragm used to provide confine for post-tensioning anchor zone and prevent spalling where a huge concentration of stress is developed due to post-tensioning of the group of tendons. vertical post-tensioning is internal and stress and grouted at the precast yard.
- vertical post-tensioning for web: vertical post-tensioning for webs used at the location of high shear near the pier to control principle tensile stresses and avoid cracking. attention shall be given to details to ensure a proper connection with the top and bottom slab.
- Post-tensioning for hammerhead piers: post-tensioning could be used for large hammerhead with long cantilevers. post-tensioning can be used to reduce the depth to produce sufficient vertical clearance where it is required. these tendons are stressed and grouted after the pier hammerhead attains the desired strength
- Post-tensioning for straddle bent: straddle bent used to support multi-level interchange. in the event of vertical clearance restriction. in this case, large depth of straddle bent may restrict the vertical clearance. therefore, post-tensioning used to reduce the depth of straddle bent. these tendons are internal and prestressed and grouted after straddle bent concrete attains the desired strength.