Finite Beam Element Model Of Steel-Concrete Composite Box Girder Bridge Considering Various Mechanical Behaviors And Time-Varying Effects

Steel-concrete composite beams are booming in the field of bridge engineering in China due to their excellent mechanical performance,construction performance and good economy.Many scholars have studied its mechanical performance,but the current research on its multiple mechanical behavior,time-varying effect and general calculation model is not comprehensive.Therefore,this thesis used theoretical analysis,numerical development,statistical fitting and other methods to study the multiple mechanical behavior and time-varying effects of composite beams.At last,a concrete shrinkage and creep calculation subroutine and a composite beam finite beam element model considering shear lag,interface slip and shrinkage and creep were developed,and the mechanical performance of the box composite beam bridge was analyzed based on the beam element model.Considering that the traditional simplified calculation method of concrete shrinkage and creep is difficult to meet the accuracy requirements of the calculation of complex bridge structures,this thesis analyzed the mechanism and influencing factors of concrete shrinkage and creep,and the calculation theory and prediction model of concrete shrinkage and creep was discussed.Based on the creep stepwise recursive calculation method,the calculation formulas of creep strain under one-dimensional stress state and three-dimensional stress state were derived.Based on the subroutine interface provided by Abaqus,a subroutine for calculating concrete shrinkage and creep was developed.Finally,through many experimental studies reported at home and abroad,the accuracy and applicability of the subroutine are verified.This subroutine can be used to calculate the shrinkage and creep of the bridge structure model established by Abaqus,and also lays the foundation for the development of the shrinkage and creep function module in the subsequent beam element model.In order to fully consider the mechanical characteristics of composite beam shear lag,interface slip and shrinkage and creep effects,and simplify the modeling calculation process of composite beams,The element stiffness matrix,element equivalent node load matrix and coordinate transformation matrix of the composite beam were derived by introducing the warping displacement function and the section angle to calculate shear lag and interface slip in this thesis based on the Euler Bernoulli beam and the principle of virtual work.Using the creep stepwise recursion method derived in Chapter 2 to calculate the shrinkage and creep of concrete,an 18-degree-of-freedom analysis model of straight-web box composite beams was constructed.The composite beam finite beam element model that can consider shear lag,interface slip and shrinkage creep was developed using Python language,and the correctness and effectiveness of the beam element model were verified by the Abaqus finite element model.The beam element model can simplify the analysis and calculation of composite beams and is the cornerstone of subsequent parameter analysis.Finally,based on the developed finite element model of composite beams,the thesis analyzed the parameters of simply supported box-shaped composite beams.The general law of composite beam shear lag,interface slippage and shrinkage creep effects affected by factors such as cross-sectional position,slip stiffness,wide-span ratio,high-span ratio,concrete grade and loading age were obtained.