Entwicklung eines effizienten und dauerhaften Verankerungssystems für vorgespannte eingeschlitzte Kohlefaserlamellen zur Bauteilverstärkung

Strengthening of buildings is a new engineering task. Changes of use, retrofitting of buildings or functional changes often have an impact on the building structure and require a strengthening method.
Strengthening with prestressed near surface mounted (PNSM) carbon fibre rein-forced polymers (CFRP) is a powerful technique, where a CFRP-strip is placed and prestressed in a groove within the concrete cover. The utilisation of CFRP can be in-creased and the advantages of PNSM are the activation of dead loads and a better per-formance for deflection as well as cracks. But the prestressing action is very elabo-rate, and often very expensive anchorages have to remain on the structure, which must be protected against corrosion.
For these reasons the PNSM-Method is further developed:
 Step 1: Prepare a groove, pretension and bond the strip to the structure
 Sep 2: Removal of the prestressing device and implementation of a permanent bond anchorages made of epoxy raisin
By using the Composite Wedge-Technique a prestressing unit for the PNSM-Method could be developed, which operates within the concrete cover and uses the wedge technique and a friction interface. The force can be applied fast and simple. The de-vice for PNSM was tested in experiments and numerical simulations. It is possible to anchor strips with a width of 2,5 mm up to ultimate CFRP-strength at 3100 N/mm² (failure appears on the free strip length). An approximation procedure is developed for design purposes, where the affinity between stress and stiffness distribution is used.
The functionality and bearing behaviour of the further developed PNSM-Method and permanent bond anchorage were investigated by experiments and numerical simula-tions. Push and pull tests and a long term test were conducted for the bond anchor-age. In 2 testing series plates and beams were strengthened with PNSM. The main advantage of the developed strengthening method is that the prestressing unit can be reused. This enables cost advantages compared to existing prestressing systems and the strengthening process only requires the durable materials epoxy and CFRP. The result is a smooth surface of the strengthened building.
Subsequent to the experiments, a design approach for PNSM strengthening was de-rived from the test results and a proposition was made.