Stressing CFRP Plates

CFRP (Carbon Fibre Reinforced Polymer) strengthening in construction has been around for over 30 years now, and the use of stressed steel wires embedded in concrete even longer. If we put the two together we get the added benefits of being able to retrofit the structure with external 'reinforcing', which can be stressed to increase it's load carrying capacity & stiffness (as opposed to just bonding the CFRP plates onto the structures) and the fact that the system is 'active' from the day it is installed.

The stressing of CFRP plates to increase the load carrying capacity, as well as the flexural strength of concrete, steel, timber & masonry structures is not a new system/technique. It was first used approximately 20 years ago, but for some reason fell out of favour. Through a Swiss comapany, StressHead, who use the sytem predominantly for seismic strengthening and upgrades, the use of stressing CFRP plates to strengthen concrete structures has undergone a revival.

With the CarboStress system, the post-tensioned plate is anchored with a compact StressHead that remains permanently on the structure. Movable and fixed anchors are used to transfer the tensioning force into the structure and these can be combined and positioned according to the needs of the project.

The advantages of the system are;

- The CFRP plates are lightweight, easy to handle & non-corroding,
- Low space requirements for installation,
- Concentrated transfer of force at plate ends,
- Outstanding fatigue behaviour,
- High movement range – no tension loss, and
- Can be applied under operational conditions.

We do not see this as a technique/system that is going to be used in every application, but definitely one to be aware of and considered if structural strengthening is required.