The Study On External Prestressing Technique In Bridge Strengnening

With the development of our national economy, the traffic volume significantly increased. And with time accumulated, many bridges have a disease now. At the same time in a fair part of the highway bridges which designed according to old standards have been unable to meet normal demand. All of these greatly hindered the development of transportation. The idea of rebuilding these aging and dangerous bridges is neither realistic nor scientific, thus reinforcing the aging bridge is very effective way.Strengthen technical of external prestressed is an effective way, which is one important branch of prestressed system. Its principle is to use the force produced by tensioning prestressed cable to offset part or all of dead and live load in control section. And its essence is to unload to control section. Relative to the passive way such as section increment, reinforced by external prestressed hardly increase the weight of bridge, but can improve stress state of girder body and improve the bearing capacity and anticrack property. At the same time the influence to pier and traffic is small, which can save the maintenance cost. At present compared with the internal prestressed structure, the research on external prestressed structure is very little, thus the reinforced field about external prestressed structure is worse. In this paper, sum up the method of assigning external prestressed cable in simple and continuous beams according to some engineering examples. Then research the material selection, the force analysis, the theory calculation and the construction process on external prestressed structure.The first is to summarize the material selection including external prestressed cable, anchorage and deviator. Prestressed cable included three kinds of materials, which are wire, prestressed strand and thick reinforced. Production of material about anchorage and deviator divided into concrete and steel. Besides introduce the domestic and international development of new materials namely fiber reinforced plastic and its scope. Then analyze the force of the strengthen construction and the algorithm of stress increment home and abroad. Based on the existing standard design studies and theory, finish the technical design theory research of external prestressed structure, including estimating about the section of external prestressed cable and prestress losses, proofing the section strength and calculating the bearing capacity after reinforced.Next, research the quality control points and attention in the construction course in order to provide a reliable basis which may ensure the strengthen process successful. According to the anchorage of production materials, it can be divided into two kinds of the construction technology which use concrete or steel. In concrete anchorage the most important link is planting tendon, and in steel anchorage the most important link is fixing high intension screw bolt.At last, material selection, theory calculation and construction technology mentioned in this paper are adopt in the engineering example. In the end by sample analysis, the rationality of the estimating about the section of external prestressed cable is validated.