Abstract: This method is suitable for the strengthening of concrete or timber structures (1, 4) by applying prestressed Carbon FRP or Glass FRP lamella (8). Firstly, at least one groove (22) is cut into the concrete or timber structure (1, 4) along the direction in which the concrete or timber structure (1, 4) is to be strengthened. The grooves (22) are filled with epoxy resin (9) and a layer of epoxy resin (9) is put onto the entire section to be equipped with the CRFP or GFRP lamella (8). The lamella (8) will be prestressed and anchored at both ends. U-shaped brackets (24) are then being put over the two end sections of the CFRP or GFRP lamella (8) by inserting and submerging its both U-legs (27) into holes (26) filled with resin as well. These holding brackets (24) will then tightly press onto the CFRP or GFRP lamella (8) to prevent cracking or fracture of the concrete or timber and bending away of the extremities of the CFRP or GFRP lamella.