Finite Element Analysis Of Creep And Shrinkage Effect On Long-term Structural Performance Of Steel Concrete Composite Bridges

Composite Steel I girders and a reinforced concrete deck slab bridges exhibit the best properties of their individual components.In which,the concrete provides compressive strength,fire resistance and floor surface,while the steel provides high tensile strength,less weight and rapid erection.When they act together,their composite system exhibits high stiffness with smaller structural sections,smaller loads on foundation,high materials performance and reduced cost.Though many advantages are worth mentioning in using these two materials in composite,steel and concrete have different mechanical behaviors leading to complications in structural performance analysis.One of these behaviors is the time dependent properties of the concrete which lead to time-dependent deformations.When concrete in composite structure deform due to these time dependent properties of the concrete,creep and shrinkage,the deformations or strains will be transformed into secondary stresses that would be imposed on the steel I beam due to restraining effects of the connecting device resulting in redistribution of stress and consequent increase in bending moments at continuity supports,together with deflections at mid span and at negative moment sections.In deflection sensitive bridge girders,using one step simplified procedures of Age Adjusted Effective Modulus Method(AAEM)or Effective Modulus Method(EM)to evaluate these time dependent deformation effects of stress distribution and deflection is inadequate.Provisions of codes such as ACI 318 have also been found inadequate and reviewed many times as the calculated stress distributions and deflections are considerably less than actual.Thus,this thesis provides a step-by-step approach to determine shrinkage and creep induced stress redistribution and deflection in continuous steel and concrete composite bridges girders.Taking the bridge at Hebei province as a case study,time-dependent structural characteristics were analyzed in ABAQUS based on Concrete Creep Shrinking Subroutine 2.1 program.Model B3 is used to predict creep and shrinkage data in plain and fiber reinforced concretes of the slab of the Bridge girder in Creep Design Aid(CDA)MATLAB program.The prediction of creep and shrinkage using B3 model were updated using 60 days' creep and shrinkage test data measured in BJTU laboratory where the specimens taken from the bridge construction site having same age as the in-site concretes.Then the updated predictions of creep and shrinkage loaded at 28th days age were used in step by step based ABAQUS Concrete Creep Shrinking Subroutine 2.1 program in ABAQUS to undertake the time dependent performance FEM analysis of the bridge girder.This program is a Fortran language algorithm to be used with ABAQUS employing USDFLD,GETVRM,UEXPAN subroutines to incorporate creep and shrinkage deformation effects in time dependent analysis.On doing this,this thesis addressed the analysis under the assumption of full interaction of the concrete slab and the steel I beam.During the FEM analysis,field measurements of strains and deflection were also conducted by installation of sensors with high precision on specific sections of the bridge where the step by step FEM analysis focused to analyze.The result of the FEM analysis shows that the compressive stress due to creep and shrinkage from the concrete slab to the top of the I beam increases due to unloading of creep and restrained shrinkage.Tensile stress at the negative moment region at the mid span region at the bottom of the I beam also increases in time.Deflection at the negative moment section and in mid span section of the bridge girder also increases in time.The analysis results from the FEM in ABAQUS were compared with the field collected strain and deflection data for its further validation.The results from the FEM were also compared with one step AAEM and EM methods.The step by step FEM method of creep and shrinkage induced time dependent performance on the bridge girder were found to be in good agreement with one step AAEM and EM approximate methods and with the field collected data also.The thesis concluded that,the values obtained based on step by step 3D FEM analysis in ABAQUS using appropriate algorithm give better results than one step approximate AAEM and EM methods.The 3D FEM analysis in ABAQUS using the relevant subroutines that incorporate time-dependent creep and shrinkage effects of the concretes avoiding large storage of stress history,ABAQUS Concrete Creep Shrinking Subroutine 2.1 program,is an efficient tool to undertake time dependent concrete deformation effects in long term performance analysis of continuous steel concrete composite bridge girders.