Effect Of Segmental Joints In Cantilever Casting Concrete Bridges On Deflection

In recent years, many prestressed concrete continuous bridges and continuousrigid frame bridges appeared excessive downwarping (more than10cm) after about10years of service, most scholars presently attribute the the factors leadingexcessive downwarping to the shrinkage and creep of concrete, whereas ignoring theeffect of stiffness reduction at segmental joints on deflection of bridges. Due to theneglect in construction, it is generally weaker greatly for segmental joints concretecompared with monolithic concrete shaped at once casting on mechanical property.However, long-span prestressed concrete bridges generally constructed throughbalanced cantilever casting, the quantity of segmental joints can reach hundreds,which leads bridges to be discrete structure connected with numbers of weakersegmental joints rather than monolithic structure. It is potential for joints to be thefactor leading excessive downwarping, due to weakening the structure. Whereas, itis consistently assumed that structure is ideal monolith without joints in bridgesdesign and construction, and the quality of joints concrete is consistent with that ofsegments, which results in the deviation between theory and practice obviously.Thus, aiming at the effect of joints connection stiffness on deflection and thesupplement of segmental joints design of cantilever casting bridge, experimentswere conducted to assess the connection stiffness including the shear stiffness andthe flexural rigidity of segmental joints. Based on the above testing conclusions, itwas researched on non-vertical segmental joints shape differing with the presentvertical shape joints consistently adopted, and it was put forward for combined jointwhich can increase simultaneously the shear stiffness and flexural rigidity of joint.And it was educed of the effect of siffness of vertical joints and combined joint ondeflection of bridges.Shear experiments of vertical joints. The experiments includes3specimenswhich is respectively monolithic non-joints, joints roughened and joints roughenedwith shear-key according to the different shear stiffness at the corresponding jointssection. Through the analysis of the testing results of the relative deformation atjoints concering the3specimens, the reduction degree of shear stiffness and thecontribution of shearkey to enhancing shear stiffness of joints was educed. And itwas put forward for shearkey design method at segmental joints based onforementioned testing conclusion.Bending experiments of vertical joints. The3specimens in bending test aresimilar with that of the shear test(monolithic, jointed, shearkeyed) except the sectiondimensions. Through the analysis of the testing results, the reduction degree of flexural rigidity and the contribution of shearkey to enhancing flexural rigidit y ofjoints was educed. And it was presented for the relation between equivalent shearmodulus and equivalent elastic modulus of joint.Based on the experiment of vertical joint, finite element models were modeledto research non-vertical joint. Taking account of the stiffness improvement andconvenient construction, through the analysis of finite element modle with3different joint slope angle as5°,10°and15°, the contribution of different slopeangle joints to shear stiffness and flexural rigidity was educed. And it was putforward firstly for the slope angle of segmental joints which enhancing shearstiffness efficiently and constructing conveniently. Through the analysis of finiteelement modle, the contribution of different breadth and height of step to shearstiffness and flexural rigidity was educed. And it was put forward for the designmethod of stepped segmental joints.Based on the experimental conclusions and finite element model analysis, itwas put forward for the design method of shearkeyed joint、slope joint、stepped jointand combined joint.In the end, theoretical analysis was conducted to the effect of segmental jointson bridge deflection, and it was educed for the effect of stiffness of vertical joint andcombined joint on deflection of cantilever casting bridges by analysis of finiteelement models, and it was proved that the combined joint put forward in thisdissertation can reduces greatly the effect of vertical joints stiffness reduction ondeflection of cantilever casting bridges.