Analysis Of Bearing Load Capacity And Crack For Prestressed Concrte Box Girder Bridge

Prestressed concrete box-girder bridge is easy to crack. Itsload-bearing capacity supports strategic decisions of maintenance andconsolidation for authority. Based on the state of development,mechanical theories and methods, linear elasticity and non-linearity ofstructures, crack and load-bearing capacity are studied comprehensively.A set of method is presented in this dissertation. The main proposals areas following:1. Using the two generalized displacements theory of Timoshenkobeam, an analytic function of transverse displacement is determined bynode harmony condition. Element formulation is derived with explicitshape functions. This element is free from shear locking. Based on theTotal Lagrangian formulation and Von-Karman's large deflection theory,geometric non-linearity analysis formulation of Timoshenko beam isconstructed. Referring to Saafan&Brotton and Fleming theories ofBernoulli-Euler beam, stable function methods of Timoshenko beam forgeometric nonlinearity formulation are presented.2. Plate-typed shell element is constructed by using transversedisplacement's shape function of Timoshenko beam and finite tripthought. This element consists of planar stress element and thick/thinplate bending element. A quadratic displacement function is attached tolongitudinal displacement of element to present shear lag effect. Thus,tension, compression, bending, shearing, shear lag, torsion, warping anddistortion are involved into the finite segment. Based on theVon-Karman's large deflection theory and Total Lagrangian formulation,a method of nonlinear analysis is developed, and a few examples arecomputed.3. Using the membrane analogy method, a strength criterion ofconcrete is established from the view of deviatoric plane and meridians.The parameters of the criterion can be determined easily by using fourtest results or five test results. The strengths of concrete under tri-axial stresses conditions are forecasted. Based on the elastic perfectly plasticmodel and elastic-hardening plastic model, constitutive equations arederived from Hinton model, Ottosen model, Chen-Chen model andpresent model for shell element under spatial stress condition. Todetermine the scaling factor, combining method of iterative algorithm andbisection algorithm is presented to prevent scaling factor from beingdetermined in the opposite direction. Also an approximation method ispresented to scale stress back to the yield surface for elastic---perfactlyplastic model. Using the composite model of concrete, a set of method ispresented to treat with the steel stiffness and efficient prestress. Based onthe theories above, material nonlinearity method is presented forreinforced/prestressed concrete shell structures.4. Based on the analysis model and methods mentioned above, acomputer program PHDFEM for load-bearing capacity analysis ofprestressed concrete box-girder bridge is complied with finite segmentelement. Program interface is designed by using Visual Basic 6.0 virsionto carry out the notepad function. A lot of famous benchmarks areanalyzed to check these computing modules. The spatial mechanicalproperties, crack and load bearing capacity of WULI Booth bridge areanalyzed. During the analysis, three loading cases are computed. Thesafety coefficients and some important conclusions are drawn fromcomputational results.