Research And Application Of Long-term Creep And Shrinkage Effects On Reinforced Concrete Structure

Time-dependent creep and shrinkage effects are the intrinsic characteristics of concrete. Both the effects always develop with the construction of building structures and members and the whole service life, and bring the long-term work performance of the structures and members significant influences.The subject about concrete creep and shrinkage effects has been researched through the last several decades at home and abroad. There have been rich achievements about the basic mechanics of concrete creep and shrinkage, the prediction models and calculation methods for the effects, and the long-term effects analysis of bridge and hydraulic concrete structures. While, in civil and construction engineering structures the development of concrete time-dependent effects has fallen behind the other structural subjects. The main lag problems include that, most of the current calculation methods of creep strain are inefficient, the research on long-term influences of steel is lack, the current software pays little attention to the time-dependent effects analysis of building structures, the long-term effects are easy to be neglected or solved by simply and rough methods in the actual project design, and it is hard to master the rules of time-dependent effects of the whole structures, and etc. For example, there is a super tall building in Doha, with incorrect tender design and neglect of long-term effects. It is shown that the long-term uneven compressive stresses in vertical members would cause obvious sideway deformation so as to influence the long-term service of building. Therefore, it is extremely urgent and significative to build the systemic research methods of the time-dependent effects of concrete structures and members, advance relatively practical calculation methods and effectively solute actual problems of projects.Based on the above problems, some research work is developed in this subject. The main research contents and achievements of this subject include successively, the optimization of basic calculation method of creep, the long-term analysis of R.C. members (member bar, shell), and whole structures (super long, tall). These researches are advanced gradually in due order and deeply step by step, stated in detail as follows:The current analysis models and theories of creep and shrinkage strain is induced and unified. The stress impulse function is built up applying the recovery theories of concrete creep. And a new recurrence method of total variables of creep strain is presented, which only need the memory of finite steps of stress changes. The recurrence method is suitable for all types of creep models and loading modes, and can effectively enhance the calculation efficiency of creep strain based on the precision requirement. The research contents about the time-dependent creep and shrinkage effects of reinforced concrete members are included as follows: the iterative method of the steel influence in axial compressive members and the equivalent method in software are deduced, and the theory of plane-section assumption is discussed. Considering the crack influence, the general analysis method and formulas of the time-dependent deflection of bending RC beam are founded, suitable for the linear or nonlinear stress distribution in the section and verified by experiments. Based on the research of deformation rules, a new multi-parameter adjustment method for the long-term deformation coefficient of bending beam is initially presented. The different analysis methods are applied in the research on the long-term effects of the little and large eccentric compressive members. Basic research on the long-term deflection of two-way slab under uniform distributional load is developed, and the time-dependent relationship among moments and angles of two-way slab is built by applying the yield line and the principle of energy. The time-dependent shear deformation of RC wall is also analyzed in this subject. The two kinds of long-term disadvantage effects of steel bar in RC members are researched, and the formulas and factors of maximum allowable reinforcement ratios are presented respectively.The basic model experimental research on the long-term shrinkage and creep deformation of concrete wall is carried out. And the applicability of current prediction models in the shell members is initially investigated. While, limited with the experimental conditions and etc, parts of the experimental results are not usable. The experiment about long-term concrete effects needs further adjustment.Considering the time-dependent concrete creep and shrinkage effects, the simplified methods of long-term temperature variables effect of concrete structures are deduced. Further, combined with the simulation of structural construction, the nonlinear FEM formulas for the time-dependent temperature variables effect of super long concrete structure are detailed presented and the analysis method is directly applied into the design and construction of an actual project.The nonlinear FEM considering the simulation of tall building structural construction and the influence of steel is built up. And the analysis procedure for tall building structural long-term effects is compiled by FORTRAN language and interface to software. To a certain degree, the procedure can make up the problems in the current software.The long-term vertical deformation difference and the side-way deformation is the typical problems of tall building structures. The simplified analysis method and basic influence factors are researched.Last, synthetically apply the research achievements into the time-dependent effects analysis of a foreign super tall building structure. The neglected important problems in original tender design are corrected. And favorable economic and technique benefits are received. The project has been completed smoothly.