Study Of Completion State Control And Spatial Mechanics Behaviors Of Self-Anchored Suspension Bridge With Extra-Wide Concrete Girder

The concrete self-anchored suspension bridge adopts concrete as the materials of tower and girder.A longitudinal self-balancing system is formed by the main cable anchored on the stiffened girder,and additional prestress is provided to the main girder.The dead and live loads are transferred to the cable trough hangers and then transferred to the tower and foundation,the structural force transmission approach is reasonable.In recent years,the concrete self-anchored suspension bridge,characterized by good economic performance,structural rationality,elegant appearance,and strong adaptability to the terrain and geological conditions,has increasing competitiveness among all types of bridges.At the same time,there are more and more concrete self-anchored suspension bridges with wide girder,promoted by the city transportation-volume growth and growing requires for vehicle lines.The width to span ratio of girder increases gradually,and even reaches 1:4.2.Based on the engineering background of Hunan Road Bridge in Liaocheng City,Shandong Province,this dissertation attempts to analyze the key technical issues of bridge completion state control during construction and operation stages,spatial mechanics behavior of the extra-wide box girder,and prediction of concrete shrinkage & creep effects for the extra-wide concrete self-anchored suspension bridge.The main contents and achievements are detailed as follows:(1)Research on the reasonable finial state determination of the concrete self-anchored suspension bridge.According to the segmented cable catenary theory,constant principle of cable unstressed length,calculation principles of free cable state and saddle offset,and concrete shrinkage & creep characteristics,a hybrid optimization algorithm is proposed to determine the reasonable finial state of the concrete self-anchored suspension bridge.The analytical cable program for suspension bridge(BNLAS)is combined with the finite element analyses.The refined finite element discrete method is adopted to simulate the changes in the contact relationships between cable and saddles.The compression values of main girder and tower due to the cable force and concrete shrinkage & creep during construction stage are well considered through introducing the rigid arm with temperature characteristics.A reasonable finial state of the bridge is obtained adopting the optimization algorithm.(2)Research on the cable system construction and structural system transformation control for the self-anchored suspension bridge.The multiple-control method during the whole process of system transformation and corresponding tension control targets are proposed,which can improve the accuracy and efficiency of system transformation control.The free installation offset of cable clip is analyzed.The general principles of system transformation control are proposed.The structural system transformation is divided into four stages based on the mechanics behavior during system transformation,including the initial-tension stage for the full-bridge,passive-tension stage for the side span,partial adjustment stage,and completion stage of the application of second-stage dead load.The control target and principle of each stage are proposed according to the multiple-control method.A detailed system transformation program is formulatee and well preformed in the construction site.(3)Research on the spatial mechanics behavior of concrete self-anchored suspension bridge with extra-wide box girder under vehicle loads.The real bridge loading test and finite element analyses based on a spatial beam-type FE model are combined.The global mechanics behaviors including the structural deformation and internal force changes under vehicle loads are investigated.The longitudinal stress levels and transverse distributions of the extra-wide concrete box girder are analyzed.The dynamic characteristics of bridge and the dynamic response increments under moving vehicle loads are researched.(4)Research on the refined spatial mechanics behavior of the extra-wide concrete box girder.An overall refined finite element model for the extra-wide concrete self-anchored suspension bridge is established,the solid element is used to simulate the extra-wide main girder,transverse girder,and anchorage area.The connections of cable system,prestressed tendons and boundary conditions are simulated accurately.The measured data is combined to study the spatial mechanics behavior of the extra-wide box girder during the prestress tension,system transformation,and bridge completion state.The transverse distribution laws of the longitudinal and transverse girder stress are analyzed,and the shear lag effects in the extra-wide box girder are evaluated.(5)Research on the development of a spatial beam element considering the shear lag effect in wide box girder.A new theoretical formulation of the spatial beam finite element considering the shear lag effect is presented.The new shear lag warping degree-of-freedom(dof)is introduced,and a series of segmental warping shape functions of the asymmetrical multi-cell box section are deduced based on the shear flow transmission law.The stiffness matrix and mass matrix of the three-dimensional Timoshenko beam element are obtained using the finite element method.The proposed beam element is implemented in ANSYS as a user defined element using the secondary development function including the Uec and Uel interfaces.The reliability of the user defined element is validated through the simply supported beam example and self-anchored suspension bridge example.The applicability of the proposed theoretical beam element is improved.(6)Research on the deterministic analysis of the concrete shrinkage & creep effect considering the shear lag effect in wide box girder.The time-dependent effects of Hunan Road Bridge are analyzed based on the monitoring data firstly.The developed user defined element in chapter V is applied to conduct the deterministic prediction analysis of concrete shrinkage & creep effect,and an overall FE model is established.The age-adjusted effective modulus method and finite element stepwise calculation method are adopted to simulate the aging behavior of concrete.The prediction results of girder's concrete shrinkage & creep strain and structural deformation are obtained adopting the prediction models including CEB-FIP 90 and B3,which are compared with the measured date to evaluate the prediction accuracies.The deterministic prediction analysis of concrete shrinkage & creep effect is conducted.The prestress relaxation is considered through updating the applied initial strains in the prestressed tendons based on the calculated prestresses during each time interval.Moreover,according to the field construction time from the casting of the concrete for each segment built sequentially to the completion of bridge,the changes in stress and geometry caused by the concrete shrinkage & creep effects during the construction stage are considered in the bridge completion state of the FE model.The uneven compressive stress changes on the extra-wide girder section can be obtained by the beam-type FE model established using the proposed beam element considering shear lag effect.The underestimated stress changes of the extra-wide box girder can be avoided.(7)Research on the random analysis of the concrete shrinkage & creep effect for the extra-wide concrete self-anchored suspension bridge.A simplified algorithm suitable for the prediction and variable sensitivity analyses of concrete shrinkage & creep effect for the complicate self-anchored suspension bridge is proposed,which can take into account both efficiency and accuracy.The environment parameters,structural parameters of bridge,and calculation parameters of B3 model are considered as random variables.The approximate moment estimation method is adopted to yield the statistical properties of structural responses including the 95% confidence limits.The efficiency and accuracy of the proposed method are validated through the comparison with the measured data.The prediction results are used to conduct a parametric study about the reasonable final state optimization for self-anchored suspension bridge considering both the concrete shrinkage & creep effect and shear lag effect in wide box girder.The hanger forces at bridge completion state are chosen as the design variables.The vertical displacement and longitudinal stress of girder are chosen as the state variables.The long-term changes of compressive girder stresses at the most unfavorable positions on the top and bottom plates affected by the shear lag effect are chosen as the target function.The reasonable ranges of pre-adjust amounts of saddles and hanger forces at bridge complete state can be determined.Some useful conclusions are drawn to provide important references to the structural health monitoring and reasonable final state determination for the similar self-anchored suspension bridges with extra-wide concrete box girder.