Experimental Study and Basic Theory Analysis on Bond-Slip Behavior between Steel Shape and Concrete in Steel Reinforced Concrete Structures

Abstract: Steel reinforced concrete structure, SRC structure for short, is a main kind of steel and concrete composite structures. SRC structural members have a relatively small sectional dimension and a high bearing capacity. SRC structures obtain a better integral stiffness, and have an excellent seismic behaviour. So SRC structures are put into application extensively. The fine bond behavior between steel shape and concrete is the base of their cooperation. The cooperation is the reflection of the advantages of SRC structures. The bond behavior directly affects the bearing capacity, failure modalities, crack, deformation and caculating methods etc.Although the calculating methods in SRC codes are different in many countries, they commonly simplify or neglect the effect of bond-slip between steel shape and concrete. There are many differences and conflicts among the present researches, and many problems about the bond-slip behavior are not solved at present. So the bond-slip behavior between steel shape and concrete encasement is necessary to be deeply studied and perfected.Considering the characteristics of SRC structurs, the paper researches the bond-slip test schemes. The axial pull-out test, as a main style, is applied, with the complement of the push-out test of 2 specimens, short-column test of 2 specimens and push-pull cyclic test of 4 specimens. The 16 specimens of pull-out test are designed according to the perpendicular test design rule, considering four parameters (concrete strength, concrete cover, steel embedment length and transverse stirrup ratio). For the research of the local bond stress and its distribution rule on the surface between the different parts of steel shape and concrete encasement, 4 specimens are adopted. The test specimens are 28 in all. The test values include the bond-bearing load, local slippage at the load end and free end, distribution values of strain of steel shape and relative slippage between steel shape and concrete along the embedment, strain of transverse and longitudinal steel, and width of the crack of concrete etc.Based on the experimental study on the bond-slip behavior between steel shape and concrete, the failure modalities are analyzed. The distribution modes of bond stress and slippage along the embedment length of steel shape and concrete interface. and their relationship and equations are provided. Several parameters that affect the bond behavior are discussed, and the bond-slip mechanism between steel shape and concrete is finelyanalyzed in interface mechanics. According to the force transfer and the punch failure principles of concrete plate, the analytical models are proposed to predict the minimum concrete covering thickness and tie reinforcement ratio, and the calculating method of the critical embedment length is also given.Based on the failure mechanism study of specimens, the stress state in the concrete encasement is ansysed and the relationships among the stresses on the interface between steel and concrete are deduced theorically. The failure criteria of bond-slip in SRC structures are proposed. The calculation equations of steel reinforced concrete structure considering bond-slip performance are established. According to the load-slip curves at the loading end, the typical bond stress-slip curve is obtained. For presenting the accurate bond-slip relationship, the equations of stress of steel shape, bond stress and relative slippage are deduced. Based on the experimental results, the laws of local bond-slip along the embedment are given. The constitutive relationships of local bond-slip are proposed. The position functions, which reflect the different embedment position, are provided. For any bond element adopted in FEM, its rigidity factors must be attained. The paper studies the bond rigidity in the two-dimensional condition. The constitutive relationship is expressed by the rigidity method only considering the stresses on the interface between steel shape and concrete.All these research results may contribute to the improvement of calculating theory of streng…
Key words: steel reinforced concrete structures; bond-slip; pull-out/push-out/push-pull cyclic/short-column test; bond strength; critical embededment length; failure criteria; constitutive relationship; bond-slip element

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