Study On Structural System And Model Test Of Concrete Etra-Dosed Bridge

The bridge structure developes with design and construction,and it is becoming lighter and thinner on the basis of meeting the functional requirements.As a new type of composite structure structure,etra-dosed bridge has attracted much attention of designers.In order to study the bridge structure system and performance,a large quantity of etra-dosed bridge projects both at home and abroad are collected to study the structure form,the key parameters and the ultimate bearing capacity on this type of bridge through theoretical analysis,numerical simulation and model test methods.The main contents are as follows:(1)The suitable structural system of etra-dosed bridge is semi floating system,beam-pylon consolidation system and rigid system,and the main difference between the three systems is the connection mode of pylon,pier and beam.Based on the method of structural mechanics,live load ratio formulas of different systems are deducted.And the formula is validated by a project,and the calculation result of the simplified formula is in agreement with the finite element calculation results,which can provide the basis for the comparison and selection in the preliminary design stage.(2)In order to study the characteristics of the main structural form of the concrete etra-dosed bridge,the finite element model is established on the basis of existing main structural forms,and the characteristics of the different components are analyzed.The calculation shows that the stiffness of the main tower affects the structural displacement and is particularly sensitive to the semi-floating system.Settig cross-beam has obvious effect on reducing the deviation of the tower and the bending moment of the tower on curved etra-dosed bridge,but it doesn't work on larger radius or straight bridges.For bottom curve of the variable height girder beam,the larger the span,the higher the number of curved curves at the bottom of box girder,the better the mechanical performance.(3)In order to determine the reasonable range of key parameters of etra-dosed bridges,this paper analyzes each parameter by establishing the finite element model system with different bridge projects.The results show that the ratio k of side span to span of bridges with three spans range from 0.44to0.68,multi spans should be range from 0.45 to 0.69,the ratio k of different systems have no significant difference.The ratio k is more sensitive to semi floating system of its support reaction force,the tower top displacement,the mid span deflection,the cable tension and the cable tension,and to beam-pylon consolidation system of its cable tension.When the smaller ratio k is used,the main beam at the side support should be pressed to prevent the bearing from bearing separation.And the larger the ratio k is,the larger the mid span cable force is.The height of pylon is the main influencing factor of live load ratio In order to ensure the live load ratio between 0.2 and 0.5,it is suggested that the ratio of height of pylon and length of span is from 1/10 to 1/6.For three non-stayed cable segments of etra-dosed bridge,the ratio of the length of tower bottom non-stayed cable segment and the main span is suggested from 0.15 to 0.20,the ratio of the length of mid-span non-stayed cable segment and the main span is suggested from 0.2 to 0.35,and the ratio of the length of side-span non-stayed cable segment and the main span is suggested from 0.20 to 0.35.This part of the research results can provide reference for similar bridge design.(4)In order to compare the ultimate load capacity of the three systems under operational load,a nonlinear finite element model of three systems was established to compare the ultimate bearing capacity of the key sections of the main girder section and the stay cables.The results show that the breaking sections of three systems are different.As that of the semi floating system breaking load coefficient ? is minimum,and the most easily damaged section is cable and the bottom pylon.But the most easily damaged section for beam-pylon consolidation system and rigid system is the girder section near the span centre in mid-span.(5)A rigid system etra-dose bridge model is made by a real bridge.The construction processes of the bridge and operation conditions are simulated.Comparing the test data and theoretical calculation results,they show that,the research methods combining theoretical calculation and model test can reflect the mechanical characteristics of construction process and operation stage.And beam element can reflect the changes of structure deformation and cable force accurately,but cannot reflect the local stress like shear lag effect.The measured data agree well with the theoretical calculation data,which shows that the model design is accurate.The model reflects the safety factor of structure construction process and operation safety is high.Based on the overload conditions results,suggestions on the structure management and monitoring are provided.