Study On Key Construction Technology Of Large-tonnage Prestressed Concrete Box Girder

Large-tonnage Prestressed Concrete Box Girders has been widely used in modern bridge construction because of good overall performance, high rigidity, good stability in the process of construction and use, and suitability for long-span bridges and complex bridges. With the continuous innovation of bridge-type and the continuously increasing span, box tonnage is increasing, too. As the bridge construction is a comprehensive discipline involved structural design, building materials, construction techniques and geographical environment etc., many new technologies and new problems will naturally follow in the construction process. The project of large reinforced concrete cable-stayed bridge and lead in Liangji Canal, Taibai Tower West Road, is a new bridge structure of recent years, which has very difficult construction, but has little reference experience. So we did special research on some key technology of large-tonnage prestressed concrete box girders of reinforced concrete cable-stayed bridge.With relevant documentation and the research and analysis on character of the project and difficult points of the construction, we summarized some points of key technology as follows on the base of relevant documentation, experiments, and site monitoring:(1) On the premise of locally-produced materials, we make optimal design and research on the mix proportion of C50 high performance concrete on the ground of orthogonal experiment, and advance some relevant construction suggestions to the mix proportion of the reinforced concrete. (2) On the ground of the experiment results of the compressive strength of the C50 test block under the standard curing conditions and the same curing conditions, we make the growth curve of the concrete strength relevant to actual projects, using math software; we advance "double-control method" to predict the strength of concrete:we use the concrete strength under the standard curing condition to control "the strength of material concrete", and create the improved BP nerve net model on the ground of L-M algorithm; and we predict "the strength of structure concrete" on the base of concrete strength under the same curing condition. Besides, we predict the development of concrete strength, using the maturity monitoring system, and give suggestions about the time to apply prestress and form removal. (3) On the base of systematic exposition of every performance indicators and process improvement of pore canal mud jacking, we did experimental research on the combination of NC-F1 water reducer and NC-P1 expanding agent, and JM-HF special pore canal mud jacking agent separately under the thread of fixed water binder ratio and changeable water blinder ratio, and we got the suggestion about the reasonable mud jacking mix proportion and relevant measure. (4)For the temperature crack of the construction of large tonnage prestress concrete cast-in-situ box girder, we did three-dimensional solid emulation analysis, and summarized law of development of strength, temperature field and stress field, and gave the suggestions about relevant method of temperature control. In addition, we did contrastive analysis with the practical monitoring result, and the result showed that using finite element analysis method to control temperature and crack is financial and effective. (5) As the importance of the combinative reinforce and concrete part of the main girder, and the lack of mechanics research of early age, we did finite element emulational analysis on it, using Midas/civil software, and summarized the law of development of time varying temperature field and timetabled stress field of the combinative reinforce concrete box girder. At the same time, we predict the key site that is likely to be damaged, and give the key section that we should pay more attention in the design and construction process, and advance some relevant suggestions.The key construction technology of large-tonnage prestressed concrete box girders,which is proposed in this paper,performs well in practical projects. It provides an important reference for the similar bridges construcing in the future and a theoretical and experimental basis for future in-depth research,as well.