System and method for reinforcing structures with pre-stressed fibre-reinforced-polymer laminates

Abstract

The current invention discloses a pre-stressing system and method for retrofitting of reinforced concrete members with externally bonded CFRP laminates in bending, according to the independent claims 1 and 8. [0011] The pre-stressing system (device) comprises a clamping unit, a light frame for hydraulic jack and anchoring plates. The clamping unit consists of tempered steel grips with a corrugated surface, which are tightened with high strength bolts in a steel frame. Usually, the result of using corrugated surface steel grips would be fractured laminate. The solution of this invention is to add epoxy adhesive on both upper and lower contact surfaces of the grips and the laminate and tighten with high strength bolts in the steel frame. The result after one day of hardening is more effective clamping unit with very low slip potential. Such units can be attached on both sides of the laminate one day before strengthening outside the construction site, this way strengthening time is not higher than using any other existing method. Alternatively, if one day does not make any difference, the clamping unit can be attached on one side of the laminate and the other end can be anchored to a concrete member with riffled surface steel plates, epoxy adhesives must be added onto concrete-laminate, laminate-steel plate contact surfaces and the plates must be tightened to the concrete member with anchor bolts at once. Anchoring with plane surface plates would not withstand similar loads, even bonded with epoxy adhesive one day before the tensioning. [0012] The main working principle of the system is that hydraulic jack in steel frame pushes the clamping unit through the hinge while the other side of the laminate is anchored.. The anchoring plates are added by the same principle described above between the clamping unit and the frame of hydraulic jack. Next, the applied force is transmitted from the jack into the frame through bolts and the jack can be removed. After full hardening of the adhesive, the hydraulic jack is returned to the frame and a force of the same magnitude is added to the clamping unit. The bolts are released and the force is slowly removed, transferring pre-stressing force into the anchors and concrete-laminate joint. The improved anchors and clamping unit reduce the risk of the FRP laminate slipping in the clamping unit and the anchors and thus the failure of the concrete-laminate joint.