Durability-Based Design For High Performance Prestressed Concrete Structures

With the introduction of high performance materials(high performance concrete and high strength low tension steel bars),Prestressing technique is widely used in large span structures, prefabricated members,beam bridges and many other special-type structures.In many years of the application of prestressing,the durability performance of prestressed concrete structures is extremely concerned by structural designers.Because of the difference of the materials used and its baring characteristic,prestressed concrete structure has a different durability performance than ordinary concrete structure.Based on the present study on the durability of concrete structure and prestressed concrete structure,the following seven aspects are covered in this dissertation:(1) After summarizing the failure status and failure mechanism of stress corrosion,analyzing the several causes of stress corrosion,this dissertation carried out technical solutions to avoid or reduce the possibilities of corrosion failure of prestressed concrete and improve the durability of prestressed concrete structures.(2) Based on the analysis of failure mechanism of prestressed concrete,cracking was found as the main cause influencing the durability of prestressed concrete structures.This dissertation also analyzed the affects of cracking during the different periods of prestressing steel bar corrosion process.(3) With the analysis of 50m span PRC beam's stress and deformation in the process of concrete curing,straining and employment,this dissertation derived the shrinkage strain allocation of large span PRC structure.By calculating the losses of concrete shrinkage and concrete creep strain,this dissertation derived the affects of shrinkage and creep strain deformation to PRC steel bars.During the test,it also depicted the cracking expanding before and after casting.(4) Through FEM modeling,simulating the casting process of prestressed concrete structures and analyzing the location of cracking during the casting process and solution,this dissertation established feasible casting schedule to reduce the possibilities of initial cracking of PRC structure which thereby will cause durability corrosion.(5) This dissertation carried out variation of the stress and strain on most disadvantage combination of loads in the PRC beam and bearing status in PRC steel bar through FEM calculation simulating the stress variation of different location under the loads in use of the prestressed concrete PRC beam.(6) A feasible evaluation scheme on durability was presented through durability testing to bridge in use and analyzing different elements affecting corrosion failure of PRC,which also estimated the life of structure in use.(7) Through FEM calculation,after simulating concrete structure shrinking by temperature stress, analyzing the stress and strain during the concrete shrinking process of large scale and continuous basement,location of max tension strain could be found.Prestressed Concrete Design Method was derived of Large Scaled and Continuous Basement with the Consideration of Concrete Shrinkage,which expand the usage of design method in current code especially for large scale and continuous basement designing.