The appearance of prestressed FRP laminate makes the structure reinforcement change from passive reinforcement with lagging force to active reinforcement. With the expansion of the application of prestressed FRP laminate, more and more projects have been affirmed.

Prestressed FRP laminate

Carbon fiber laminate is the most important part of prestressed carbon plate reinforcement system. The quality of carbon fiber laminate  is directly related to the ultimate bearing capacity. The carbon fiber laminate is a composite material, which is made of carbon fiber precursor and impregnated resin through pultrusion process. Its mechanical properties are mainly determined by the content of carbon fiber precursor and the interfacial compatibility between precursor and resin.

In the prestressed FRP laminate reinforcement project, the active force is realized by tensioning and prestressing, and the tension tonnage of the prestressed FRP laminate is different in different reinforcement projects. Does the continuous increase of tension tonnage mean the continuous improvement of carbon plate quality? In fact, the tensile tonnage of the FRP laminate is calculated by the tensile stress and the cross section of the carbon plate. Taking the tensile stress control of 1200 MPa as an example, the tensile forces of 1.4 mm, 10 cm width, 3 mm and 10 cm width of carbon sheet are respectively:

1.4×100×1200/10=16800kg=16.8t

3×100×1200/10=36000kg=36t

It can be seen that under the premise of the same tensile stress of 1200 MPa, the tensile force of different section sizes of carbon plate is completely different, and the tensile failure of carbon plate caused by excessive tensile stress is the easy failure form in reinforcement. Therefore, it is obviously unscientific to evaluate the quality of carbon laminate by the magnitude of tension without mentioning the tension-controlled stress, which is also one of the pitfalls in the selection of prestressed carbon FRP laminate.

Prestressed anchor device

Anchorage plays the role of clamping and transferring load in the whole prestressed carbon plate reinforcement system. Only when the anchor has effective anchoring effect, the prestressed carbon plate can play its high strength. In the actual prestressed carbon plate engineering, due to the failure of anchorage, the carbon plate is no longer a small number of anchorage, slippage, so in order to ensure structural safety, we must have enough attention to the performance of anchorage.

We can consider the performance of anchorage from two aspects, one is the efficiency of anchorage, anchorage efficiency is low, carbon plate in the process of tension, easy to take off anchorage, can not play the high strength of carbon plate, not only the bearing capacity of small increase, but also a waste of high strength carbon plate. In addition, in order to ensure the long-term effectiveness of the prestressed carbon plate reinforcement system, the anchorage must have sufficient long-term fatigue resistance to prevent the failure of the whole reinforcement system caused by anchorage failure in long-term use.

Of course, in addition to quality assurance, cost is often a major factor in the selection of prestressed FRP plate. However, the reduction of cost is not equal to Jerry building, but should be reduced by technological innovation. HM prestressing carbon FRP laminate, while continuously enhancing the strength of carbon laminate to reduce the number of at the same time, the form of anchorage is constantly innovative. Now not only has a variety of anchorage forms, but also demountable anchorage has been applied and recognized in a number of projects, and new breakthroughs have been made in the cost savings of prestressed carbon plate system.