| Reactive powder concrete(RPC)is a kind of super high performance concrete with super high strength and excellent durability,but similar to high strength concrete,RPC has poor ductility and its failure mode belongs to brittle failure.RPC is poured into steel tube to form RPC filled circular steel tube.Through the restraint of steel tube,this material can effectively overcome the weakness of brittleness,give full play to the excellent properties of the two materials,and has a wide application prospect.The bond force between steel tube and concrete is the premise for the two materials to work together,at present,there are many studies on the bond-slip behavior and constitutive relationship of ordinary concrete filled steel tube at home and abroad,but there are few studies on the bond behavior between steel tube and RPC,which is still in its infancy.There are still some deficiencies in the research of factors affecting the bond-slip behavior of RPC filled circular steel tube,theoretical research and numerical simulation analysis.In this context,the bond-slip behavior of RPC filled circular steel tube is studied by means of experimental study,theoretical analysis and numerical simulation,which mainly includes the following aspects:(1)Experimental study on bond-slip mechanics behaviors of structures RPC filled circle steel tubes.Through the axial monotonic push-out test of RPC specimens of circular steel tubes,the failure modes of bond-slip of RPC specimens are analyzed,the failure mechanism is discussed,the load-slip curve is analyzed,the value principle of bondfailure load is clarified through force analysis,and the influence rules of diameterthickness ratio,length-diameter ratio,RPC strength and hoop coefficient on bond performance are discussed.The study of strain distribution of steel tube strengthens the understanding of restraint mechanism of steel tube.(2)Research on calculation method of bonding strength of RPC filled circular steel tubes.By converting bond load into bond stress,and through comparative analysis of domestic research on calculation methods of bond strength of concrete filled circular steel tubular,the advantages and disadvantages of each calculation formula are discussed,the influence of single test parameter on bond performance is studied,and the functional relationship between single parameter and bond strength is fitted,according to the fitting results,the formula with the ratio of the stirrup coefficient to the length-diameter of the specimen as the parameter is selected,and the statistical regression of the test data is carried out,the undetermined coefficients in the formula are determined by the fitting method,and the calculation formula of bond strength of RPC filled circular steel tube is established.(3)Research on constitutive relation of bond slip of RPC filled circular steel tube.Taking RPC contact interface of circular steel tube as a separate research object,the average bond stress-slip curve of loading end of specimens is classified,the fitting degree and complexity of the formulas in the formulas library are compared and analyzed,and the formulas of the curves in each stage are determined,and the statistical regression of the test curves is made,the method of selecting the undetermined coefficients is determined by fitting method,and the mathematical expression of the average bond stress of RPC filled circular steel tube is established.The relationship between bond stress and longitudinal stress and strain of steel tube is analyzed theoretically,based on the distribution of longitudinal strain along the length direction of the steel tube wall during loading and the balance of forces on the interface,the distribution function of bond stress is proposed.Finally,the constitutive model of bond slip of RPC filled circular steel tube is obtained.(4)Numerical simulation of RPC filled circular steel tubes.By using the finite element program ANSYS,a new finite element model is proposed,which combines the contact element with the non-linear spring element.According to the bond-slip constitutive relationship of RPC filled circular steel tube proposed in this paper,a new finite element model is adopted to simulate the test specimens in a non-linear way,the validity of the position function is verified by comparing the results of the finite element calculation with the experimental results.The stress of the steel tube and RPC in the whole loading process is discussed and the test is supplemented. |
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