Establishment Of Curved Composite Box Girder Elements Considering Multi-mechanical And Time-dependent Effects

Curved steel-concrete composite box girder bridges have the advantages of light weight strong spanning capacity and large torsional rigidity,and have been widely used in the construction of urban highway overpasses and ramp bridges.Compared with straight beams,curved composite beams have obvious bending-torsion coupling phenomenon,and their mechanical behavior is more complex.In addition,under the action of long-term load,the shrinkage and creep of concrete will make the long-term performance of curved composite beams more complex.Although the three-dimensional fine finite element model can effectively analyze the mechanical behavior of curved composite beams,its modeling efficiency is far less than that of one-dimensional beam element model.Firstly,a curved steel-concrete composite beam element model with 2 nodes and 22 degrees of freedom is proposed on the basis of studying the existing beam element model.The degrees of freedom in the model include radial displacement,vertical displacement,tangential displacement,torsion angle,distortion angle and relative slip of steel-concrete interface.The model can effectively analyze the torsional warpage,distortion warpage and bi-directional interface slip of curved beams.Then combined with Ansys fine finite element model,a simple curved steel-concrete composite beam is analyzed and calculated,which verifies the correctness of the theoretical model.Through the theoretical model,the effects of initial curvature,number of diaphragms and shear stiffness of shear connectors on the curved composite beam are discussed.Thereafter,in order to solve the large curvature effect and shear lag effect caused by the excessive width-span ratio of curved beams,the shear lag warping strength function of concrete slab and steel bottom slab is introduced on the basis of the above-mentioned beam element model,and the curvature variation along the beam width direction is considered.A 2-node 26-degree-of-freedom curved steel-concrete composite beam element model is presented,which can effectively consider the large curvature and shear lag effect of curved beams.A large curvature curved composite beam is calculated and compared with Ansys fine finite element model,thus verifying the correctness of the theoretical model.Then,the theoretical model is compared with the calculation model without considering the large curvature effect,and the shear lag effect of curved beams is simply analyzed and discussed.Finally,in order to solve the long-term performance problem of curved composite beams caused by concrete shrinkage and creep,after comparing and studying the commonly used theoretical methods for calculating concrete shrinkage and creep,this paper presents a beam element model which can effectively consider the long-term performance of curved beams based on the age-adjusted effective modulus method and verified by the Ansys fine finite element model.Then,the long-term performance of Curved Steel-Concrete Composite beams is briefly analyzed through the theoretical model.