Research On Cracking Control Technique Of Concrete Thin-wall Pier In Cold And Dry Region

Due to the cold and dry climate, a great temperature difference between day and night, and frequent action of cold wave, concrete structures in the north of our country are liable to generate structural cracks. Especially, surface area of thin-wall pier structure is relatively larger, which makes all kinds crack phenomena, such as crack, flaw and fracture, occur easier in the early stage of setting. Once thin-wall pier cracks, durability, impermeability, corrosion resistance and aesthetics of whole bridge will be influenced to some extent, and service life of bridge will also be reduced greatly. So how to prevent cracks of concrete structures effectively becomes an issue which absorbs long-term concern of engineers.Focused on the construction of thin-wall piers of K93+737 Bridge on Lot 2, the segment from Saliba to Xiawa, on Chifeng-Tongliao Highway in Inner Mongolia, a more thorough research on cracking control technique of concrete thin-wall pier in cold region is carried on. The main contents are as follows:1. Influences of various ingredients of concrete on integral crack resistance of concrete thin-wall pier are analyzed. A series of selective preference on raw materials of concrete are put forward. Main parameters in concrete design, such as use level of gel, content of fly ash, content of additives and sand rate, are tested and quantitative analysis of concrete mix is performed by Temperature-Stress Testing Machine. Concrete match satisfied with the requirement of crack resistance is designed so as to increase self crack resistance and improve self deforming performance of concrete.2. Based on the application of ANSYS, a general FEM software, variation of temperature and stress fields of thin-wall pier under various construction conditions is emulated. Macro command is compiled with ANSYS Parametric Design Language, calculation flow and live and dead of elements are controlled according to construction process, so variation of temperature field of thin-wall pier under different construction stages is simulated; influences of temperature stress due to temperature changes and drying shrinkage stress due to moisture variation on cracking of the structure are superimposed, and stress development of each part of thin-wall pier during construction and its effect on integral performance of concrete structure are analyzed comprehensively.3. Overall supervisory is carried on during construction of thin-wall pier. Site temperature monitor is performed, temperature variation rule of thin-wall pier during concreting is analyzed, and actual measurement result is mutual verified with theoretical calculation. Meantime, by utilizing sufficiently various existing conditions in site, construction technology of thin-wall pier is strictly controlled according to the requirement of crack resistance so as to ensure construction quality and integral performance of concrete thin-wall pier.