Research On Problems Of Crack Control In Large Platform Of Nanjing Olympic Sports Center

The application of large area prestressed concrete beam-slab frames in civil engineering becomes more and more abroad. The crack problem in this structure puzzles the designers. In this paper, how to control the development of crack is deeply studied, based on large platform structure of Nanjing Olympic sports center. The main work is as following.1. Nearly one year observation is carried in the Key Laboratory of PC & PRC structure and the site of Nanjing Olympic Center. The variation of basis properties of concrete, such as strength, elastic modulus, shrinkage and creep, versus age, is recorded. Based on comparison of long-term observation and the existing formula of material properties versus age, an anastomotic design mode is received, expecting consultable use in similar project.2. Based on analysis and summary of domestic and foreign exiting research result, the measures that how to control the development of crack in concrete frame is deeply studied. Quantitative analysis on the proper expansion joint is performed, and theoretic arithmetic formula is put forward. The set manner of joint is studied and proper measures are presented. Considering the application in projects, the reasonable layment of prestress steel and general steel in large area prestressed concrete beam-slab frame is discussed.3. The finite element model of Nanjing Olympic Center is created, and the distribution of internal force under temperature and shrinkage load is analyzed. It is indicated that cirque concrete frame has its own character besides something like ordinary frames.4. Under temperature load, tension stress in the middle span is big in multi-span concrete frames, and the bigger node displacement of side column causes considerable additional moment in beams and columns. In order to reduce the stress and the lateral displacement of columns due to temperature, sliding supports are disposed in different manners. Analysis indicates that it is a effective measure.5. Two different structure projects are presented, which adopt different continuous spans of prestress steel and expansion layout. Considering usability, economy, operability and the structure performance in construction stage, the two projects is compared, and selecting the better one.6. Analyzing and dealing with the record data of the site of Center Platform, and summarizing.