Theoretical Analyse And Experimental Research On Bending Behavior Of External Prestressed Composite Steel-Concrete Beams

The external prestressed composite steel-concrete beams are new structures which have developed from common composite steel-concrete beams. Compared with common composite steel-concrete beams, the structures have several excellences, which could exert high strength steel performance adequately; enlarge the elastic range of steel and advance the stiffness; reduce height and dead load of the beams; increase the ultimate capacity; debase the effective stress amplitude of steel and improve the fatigue performance. These merits get the external prestressed composite steel-concrete beams bright applying foreground in engineering.The composite steel-concrete beams can be divided into full composite beams and partial composite beams according to the degrees of shear connection. Taking into account the mechanics behavior and economical efficiency, the partial composite beams are applied in actual projects. When the partial composite beams are loaded, the interface of steel and concrete would generate slips. The slips make the assumption of plane cross section disaccorded and decrease the stiffness, so stress and deflection are affected by the slips rather deeply. So far, the theoretical research on this aspect is inadequate and the code is not perfect, hence the composite steel-concrete beams have not been taken into application and generalization in engineering. This paper carries through research mainly on the following aspects:(1) Experimental study on external prestressed composite steel-concrete beams. Through studying the bending behavior of four external prestressed composite steel-concrete beams, it is analyzed that degrees of shear connection and prestress affects the performances of this type of beam, including slip, deflection, strain, crack and flexural capacity.(2) Beginning with analyzing the slip, the slip effect impact the deflection and strain of steel-concrete beams are researched. Through analyzing the interface of steel and concrete stresses, it is derived that the calculating formulas, which are about the slip and the slip strain under uniformly distributed loads and two symmetrical concentrated loads. Moreover, the formulas of stress and deflection are suggested.(3) The relationship between the strain increment of external prestressed tendons and the whole structural deformation. Through establishing the mechanical model, the formula about the relationship between the strain increment of external prestressed tendons and deflection are derived, and the calculated values coincide with the experimental results well.(4) It is researched that the bending behaviors of external prestressed composite steel-concrete beams in service ability limit state.(5) It is researched that the ultimate flexural capacity of external prestressed composite steel-concrete beams in ultimate limit state of carrying capacity, and the relevant formula are derived.