For strengthening pre-stressed concrete beams or slabs, simple externally bonded strengthening systems may not be sufficient. In these situations the strengthening system may need to be tensioned to provide an active strengthening system and be able to enhance the load carrying capacity of the structure in conjunction with the existing built-in pre-stressing system.

In most cases the post-tensioning system is designed with the following external components: fixed anchorage system located towards each end of the beam/slab, and post-tensioning cable that tensioned between the two anchors then locked in a tensioned state. The tensioning cable can be regular high tensile multi-strand steel, rigid carbon fiber rod, or carbon fiber fabric. The post-tensioning cable can be bonded or un-bonded along its entire length. The end anchorage system can be made of either concrete that is doweled into the existing concrete, or could be manufactured of structural steel that is bolted to the structure.

The pre-stressing process of the external strengthening system is the same as the process used for any other conventional post-tensioning project.

Applications:	Bridges, Parking Structures, Buildings, other industrial concrete or steel structures
Benefits:	Increases load capacity of the structure to design specifications Cost effective alternative to the only other option: remove and replace Minimal construction time required Requires minimal or no disruption to traffic/plant operation
Sample Project Histories	Bridge Girder (PDF)

See also:
Advanced Composite Materials
Structural Steel

Precast/Pre-stressed Concrete Repairs

Post-Tensioned Concrete Evaluation and Repair Solutions

Post-tensioning Evaluation