| Featured with excellent mechanical properties and high economic benefits,concrete filled steel tube(CFST)and concrete filled steel box(CFSB)are the steel-concrete composite structures which are widely used in industrial buildings,high-rise buildings and bridge structures.Prestressed concrete-filled steel-box beam is a new type of construction member subjected to vertical load and bending mostly based on concrete filled steel box.In addition to the advantage of concrete filled steel box,it also possesses higher stiffness,bearing capacity and seismic performance than the conventional beam structure.Prestressed concrete-filled double-webbed I-shaped steel-box beam is an improved structure which optimizes the section form of prestressed concrete-filled steel-box beam.Its stiffness and load transmitting capacity of superstructure are stronger,and it has been applied preliminarily in bridge engineering at present.Nevertheless,the domestic research on prestressed concrete-filled steel box is still in the initial stage,and there are few pertinent literatures and still a lot of problems to be verified about its stress characteristics.In this paper,the stress characteristics of prestressed concretefilled rectangular steel-box beam are studied according to theoretical analysis,previous testing results and numerical methods.And then,the structural characteristics of prestressed concretefilled double-webbed I-shaped steel-box beam are analyzed in depth,which provides theoretical support for the popularization and application of the structure.First of all,the paper states systematically the development and research status of concrete filled steel tube,concrete filled steel box and prestressed concrete-filled steel box at home and abroad.After that,a preliminary full-scale model test scheme was designed.Then,it elaborates the advantages of prestressed concrete-filled double-webbed I-shaped steel-box beam in engineering application and the existing problems at the present stage.Secondly,we have studied the nonlinear analysis theory of prestressed concrete-filled steel-box beam,and illustrated the analysis method intended for high nonlinearity of materials with finite element method and the constitutive relations as well as failure criteria of each component including the concrete confined by structure.Besides,we have analyzed the structural behavior of the whole process of the failure of the prestressed steel-box concrete structure,including the load-displacement relationship,characteristic point load,strain distribution mode,the influence of loading mode,the rule of concrete cracks and the rule of prestressed reinforcement stress.Combined with the test results,it is deemed that the prestressed concrete-filled steel box has the characteristics of high bearing capacity,large stiffness,good stability,material saving,ductility and superior seismic performance.Furthermore,we have studied the unique structural behavior of prestressed concretefilled double-webbed I-shaped steel-box beam,analyzed the differences of mechanics behavior between double-webbed structure and rectangular structure,and further studied the influence of six parameters on structural behavior.Combined with the results of parameter analysis,we has put forward a method for calculating the load-carrying capacity of prestressed concrete-filled double-webbed I-shaped steel-box beam.Also,the validity of the proposed method is verified by experimental results and finite element results.Eventually,a research has been undertaken for bond-slip characteristics of steel-concrete contact surface,which clarifies the concept and research theory of bond-slip.The bond-slip constitutive model is simplified for the application of prestressed steel-box concrete beam based on the bond-slip constitutive relations.What's more,according to the constitutive model,the bond-slip effect of the structure is calculated by finite element method.Combined with experimental results of rectangular beam,the validity of calculation is verified,and a calculation method is presented for the slip displacement function of prestressed concretefilled steel box as well. |
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