The Experimental Study On Strengthening Beam By Prestressed-cable-offloading Method

Enlarging concrete section, enveloping iron and strengthening with carbon fiber sheet are the widely-used methods to strengthen concrete beam. The strengthened structure is the structure subjected to twice-loading. The old structure have worked and produced stress and strain before strengthening; the new parts just begin to work only under new loading. When the whole structure is loaded twice, the strain of new parts can not reach ultimate state when the original structure damaged.By prestressing consolidation, unloading and strengthening can be achieved synchronously and the strain lagging caused by twice-loaded in other strengthening experiments can be cleared up partly or completely.The prestressed-cable-sharing-loading method absorbing the advantage of traditional prestressing consolidation is tested and researched to strengthen simple-supported beams in this experiment. The mechanism of load-dividing, stress-transmitting and adjustment of stress along section of simple-supported beams strengthened by prestressed-cable-offloading is clarified through anlysing the stress of original structure and strengthened structure, which shows the advantages of this strenghening method. This method is achieved by steel-prestressing combination construction. Cable provides prestressing force; steel frame convert the prestressing-force into equivalent uniform load in opposite direction acting on the strengthened beam, which can sharing the load partly, at the same time, increasing beam's stiffness.It is clearly that strengthening and unloading can be put into effect at the same time by the method; this kind of strain lagging between lately part and primary concrete can be cleared up effectively; the whole bearing capacity of combination construction can be improved remarkably; the defection and the crack of the strengthened beam can be improvedeffectively; the potential of the material can be aroused fully; offloading, force-transmiting and changing internal force can be achieved at the same time, which are all we predict.Mechanism of reinforcement and concrete is complicated, so how to predict the prestressing loss, and how to compute the most reasonable stretching value and optimize nodes should still be studied.