Research And Application Of Key Technology In Jointless Design And Construction For Super-Long Concrete Structures Under Indirect Load

With the rapid development of urban construction,an increasing number of super‐long concrete structures have emerged,in which expansion joints are usually avoided in consideration of the inconvenience caused by them.Dued to the particular geometry of super‐long concrete structures,stress development turns a critical issue in this kind of structures.Based on the construction of the super‐long basement foundation slab,the influences of piles and foundation on longitudinal stress induced by shrinkage and temperature variation were analyzed under the hypothesis that the constraint effect of piles was equivalent to the foundation by the scale factor.Then,the effects of the crack control methods with the post‐pouring belt,the prestressed concrete and the expansion reinforcing band were compared.Furthermore,the theoretical calculation of creep was introduced into the finite element analysis,in which the relaxation coefficient was regressed.Suggestions on the design and construction of the seamless structure were put forward based on the case study of a super‐long concrete basement project.The main research contents of this thesis can be summarized as follows:(1)The constraint effect of pile foundation of super‐long concrete basement was analyzed.Under the constraint of piles and foundation,the concrete shrinkage and environmental temperature change would induce tensile stress.First,the lateral stiffness at the top of pile was derived.The parametric analysis of the pile effects on the shrinkage stress of concrete basement slab was carried out,in which the total constraint of piles and foundation was converted into the equivalent foundation constraint in the form of proportional coefficient.The range of the proportional coefficient and the formula of fitting calculation were summarized,as well as the efficiency of post‐prestressed concrete in the super‐long concrete basement.(2)The control effects of the post‐pouring belt,the prestressed concrete,and the expansion reinforcing band were compared.The maximum tensile stress of various seamless design methods under the same conditions was calculated through the finite element parametric analysis of basement slab.In the finite element analysis,the results of the effective modulus method and the stress relaxation coefficient method were compared with the consideration the creep effect of concrete.(3)Based on the effective modulus method and stepwise calculation,an element analysis model was established in the ANSYS program,considering the creep effect.Compared with the creep effect analysis of the same model in the MIDAS program,the accuracy of the modeling was verified.The shrinkage tensile stress and its stress relaxation coefficient were calculated by the finite element parametric analysis.Last,the formula for calculating the stress relaxation coefficient of super‐long concrete slabs at different ages was proposed.(4)The formula of stress relaxation coefficient was applied to a practical super‐long concrete basement project.The tensile stress induced by the concrete shrinkage was calculated considering the construction process.The tensile stress turned out to be lower than the tensile strength of concrete at the service stage with the stress relaxation effects of creep considered,which meets the requirements of crack control.In the actual project,the stress in the super‐long concrete slab was maintained at a constant value,which was much less than the elastic one,under the interaction of shrinkage and creep.At last,for super‐long concrete structures,the key technologies of design and construction were given in terms of post‐pouring belt,expansion reinforcing band,shrinkage‐compensating concrete and prestressed concrete.