EXPERIMENTAL STUDY ON REINFORCED CONCRETE BEAMS STRENGTHENED BY EXTERNALLY PRESTRESSED VERTICAL TENSIONING METHOD

Seven reinforced concrete beams (two contrast beams and five externally prestressed beams) were tested.The fracture morphology, crack situation, and regularity of changing strain of steel bars and external tendons underdifferent stress of tension control were analyzed through exprerimental data. In order to simulate the conditions ofpractical projects, there were three kinds of test conditions in the experiment: 1 ) before loading prestress was appliedto beam; 2 ) loading to crack, then unloading and prestressing; 3 ) loading to crack, then not unloading andprestressing. Finally, according to ultimate stress theories of unbounded prestressed steel and ultimate condition theorybased on plastic hinge, it was studied the caculative method of ultimate bending moment. It was shown that theresearch achievements of unbounded prestressed structure could also apply to externally prestressed structure whensecond-order effect was small.