Research And Application Of Key Technology In Jointless Design For Super-long Concrete Structures

With the rapid development of urban construction,an increasing number of super-long concrete structures have been built,in which expansion joints are usually avoided in consideration of the inconvenience caused by them.Therefore,control of cracks induced by the temperature variation and the concrete shrinkage has become a key problem.Under the background of the construction of the super-long concrete structure in Pudong Science and Technology Innovation Park of Shanghai Tobacco Group Co.,LTD,application of shrinkage-compensating concrete and expansion reinforcing band in the jointless design of super-long concrete structures was studied from the material level,the member level and the structural level.The research achievements were applied to the actual project and desirable results have been received.The main research contents of this study can be summarized as follows:(1)The advantages and working mechanism of shrinkage-compensating concrete applied in the super-long structure were first expounded;formula for crack spacing of the shrinkage-compensating concrete was obtained in combination of the practical computation theory of super-long concrete structures in the effect of temperature and shrinkage;the finite element analysis for the basement foundation slab under the temperature effect was performed to study the influences of the length and the thickness of the base plate,and the horizontal restraint coefficient of the foundation on the stress distribution;the additional constraints of pile foundation to the structure were especially considered and the horizontal restraint coefficient of the foundation was determined.(2)Fiber reinforced shrinkage-compensating concrete was studied through the experiments based on the design requirements of practical project.Effects of the expansive agent content on the slump,restrained expansion rate and compressive strength in different ages of shrinkage-compensating concrete with three strength grades(C30,C40,C45);impacts of fiber types(polypropylene fiber,unoiled PVA fiber,cellulosic fiber)and fiber contents(0.6kg/m3 and 0.9kg/m3)on the anti-cracking property at early ages of the shrinkage-compensating concrete were analyzed through early cracking resistance experiments;the mix proportion of fiber reinforced shrinkage-compensating concrete of different strength grades were determined according to the analysis of experiment results.(3)Application effects of the fiber reinforced shrinkage-compensating concrete and expansion reinforcing band in the actual super-long concrete structures are most concerned by designers.Concrete model tests under the natural environment were conducted.Five members were designed,including one unconstrained fiber concrete member without expansive agent and two sets of fiber reinforced shrinkage-compensating concrete with different expansive agent contents.The members were monitored for 4 months.Finite element analysis was conducted for members with the reinforcing band and the creep effect was considered by using age-adjusted effective modulus method.The stress and strain development was simulated and the simulated strain values were compared to the measured strain values.(4)The shrinkage-compensating concrete and expansion reinforcing band were utilized in the actual super-long structure,and the construction period was shortened through adopting the combined methods of continuous expansion reinforcing bands,post-pouring reinforcing bands and post-pouring strips.The strain development at early ages of the field test area of the basement foundation slab was measured.The results revealed that a certain prepressing stress was produced at the early age of concrete due to the effect of shrinkage-compensating concrete,which refrained the structure from early-age cracking.It's worth noting that cracks have not been observed in the project so far,demonstrating the anti-cracking effectiveness of fiber reinforced shrinkage-compensating concrete.Furthermore,stress and strain status of filed test areas of the basement foundation slab were analyzed through finite element method,and the simulated results were compared with the measured values.The effects of width and restrained expansion rate of expansion reinforcing band were studied and the design suggestions were provided.Technical essentials of the shrinkage-compensating concrete were elaborated according to its characteristics.