Study On Concrete Creep In CFST Tied-arch Bridge

Creep is a time dependent problem with the whole life cycle of the structure.For the concrete filled steel tubular(CFST)arch bridge,in ten years or even twenty years,the creep will have a certain impact on the performance of the structure and can not be ignored.Due to the environment and the different materials used,there are some differences in creep between the concrete filled steel tubular and the ordinary concrete.The creep coefficient which considering the interaction between concrete and steel tubular were given in the Concrete Filled Steel Tubular Arch Bridge Design Code(JTG/T D65-06-2015).In this paper,the creep analysis of concrete filled steel tubular members and the whole bridge were carried out by using different codes.By comparing the results,a appropriate range of parameter values in the formula of creep coefficient of CFST were given in the paper and the mainly work done as the following aspects:1.The paper introduced the characteristics and the development of concrete filled steel tubular and its application in the structure.The present situation at home and abroad of CFST creep is briefly introduced,the mechanism and influencing factors of concrete creep are described in details.2.The calculation theory and model of concrete creep are introduced.In order to make the stress history not stored in the creep calculation process,the curve of creep coefficients was fitted by exponential function using Matlab.3.Different parameter values were used to analyze the creep effect of CFST short columns by using JTG D62-2004 and JTG/T D65-06-2015 respectively.The difference of the displacement and the internal force redistribution of the composite section were obtained,the analysis shows that JTG/T D65-06-2015 is more realistic.It is suggested that the component theoretical thickness can be taken as about 3 times of the concrete thickness,and the annual average relative humidity of the environment selection 85% is more appropriated.4.The creep effect numerical simulation of CFST arch ribs was carried out,the effects of steel ratio,the elastic modulus ratio of steel to concrete and the span ratio on the creep of arch rib is analyzed.It is pointed out that the creep effect decreased with the increase of steel ratio,the elastic modulus ratio of steel to concrete and the span ratio.In the later period of the creep,the impact of the elastic modulus ratio of steel to concrete was very small.At the same time,the development rate of concrete creep is basically same under different span ratio.5.The Midas model of the real bridge was established,the creep effects was analyzed by using the JTG D62-2004,ACI 92 and JTG/T D65-06-2015.According to the creep effect of the whole bridge structure,the variation law of displacement and internal force of arch ribs,hanger and tie beam due to concrete creep is obtained.The analytical results can provide theoretical guidance for bridge health monitoring...