| The shrinkage and creep are the inherent time-dependent characteristics of concrete materials. It is urgent to accurately estimate and predict the influence of concrete shrinkage and creep on the deflections of large-scale prestressed concrete bridges (especially the prestressed box-sectional beams in light rail trestle projects). The research on prediction model of concrete shrinkage and creep has been paid less attention at home, and the current model can't meet the requirement of modern concrete and prestressed concrete structures. The introduction about the finite element method considering shrinkage and creep of concrete is mostly sketchy, and the factors taken into account are not comprehensive, which goes against widely applications of the method. The reasonable construction time for tracklaying after completing the civil work of the Wuhan Light Rail Trestle Project has to be confirmed. Those problems urgently need to be resolved through some special research work.The mechanisims and influential factors, as well as the newly research findings, are firstly expatiated before the factors that should be involved in a reasonable prediction model are clarified. Then the the main characteristics and disadvantages of the current prediction models at home and abroad are clear understood, after the detailed comparison and commentary on the theoretical principle, factors considered and the fitting precision to the test data of those models are carried out. Based on the foregoing research and the ASRI (1986) model, which sumarried the main results of the domestic experimental research, a prOpositional prediction model for the shrinkage and creep of concrete is developed by the author. In addition, the basic equation of the age-adjusted finite element method considering shrinkage and creep of concrete in the same time is derivated by means of the energy principle before the calculation procedures of the FEM are presented. Finally, the according computer programme CAPB is compiled, to calculate the creep displacements of some partial prestressed box beams of the Line one in the first stage of the Wuhan Light Rail Trestle Project adopting the propositional model and CEB-FIP (1978) model respectively, and the calculation results are compared with the prototype observed data.Through the foregoing research work, the major findings are as follows:(1) By analyzing the mechanisims and influential factors of concrete shrinkage and creep, it is deemed that the member volumn-surface ratio have a significant impact on the developing process rather than the ultimate value of that. The compression strength of concrete have no direct relation to shrinkage and creep, but it can reflect the influences ofwater-cement ratio and cement content on shrinkage and creep, and it should be take into account in the predition model with the enhancement of concrete compression strength of current structures.(2) Comparison research indicate the GL 2000 model performs best for predicting shrinkage and creep, followed by RILEM B3 (1995) model, CEB-FIP (1990)model and ACI 209R (1992) model, among the four neoteric prediction models. So the GL 2000 model RILEM B3 (1995) model are firstly recommended in case of lack of test data and the overseas models have to be chosen.(3) Based on the comprehensive research on the mechanisims, influential factors and prediction models of concrete shrinkage and creep, a prepositional prediction model for the shrinkage and creep of concrete is developed by the author. The prepositional prediction model reveals explicit concept, considers more factors and has a better prediction precision than the ASRI (1986) model or the CEB-FIP(1978)model adopted by the design code JTJ 023-85.(4) The basic equation of the age-adjusted finite element method considering shrinkage and creep of concrete in the same time is derivated by means of the energy principle, and the shrinkage and creep analysis computer programme CAPB for prestressed concrete bridges, which involves the author's prepositional prediction model, is co... |
