Study On The Long-term Behavior Of Steel Truss Stiffened Continuous Rigid Frame Bredge Considering The Influence Of Temperature And Humidity

As the span of the bridge grows,the deflection and cracking problems of the continuous rigid frame bridge become more and more serious,which become the key technical problems restricting the further development of large-span concrete bridges.Theory and engineering practice show that shrinkage and creep are the important reasons for the deflection and cracking of the bridge.In order to improve the long-term deflection and cracking of continuous rigid frame bridges,on the one hand,it is necessary to study a mo re accurate model of shrinkage and creep to predict the long-term deformation of the bridge;on the other hand,a new bridge structure system can be used.Bridge are in the natural environment in the process of construction and operation,but at present the research on shrinkage and creep effects under varying temperature and humidity are relatively lacking.As a new type of bridge,the steel truss reinforced continuous rigid frame bridges put into use in recent years,there is little research on the influence mechanism and degree of shrinkage creep effect on such bridges.In this dissertation,the shrinkage and creep under variable temperature and humidity were exploded by experimental and theoretical methods,and the influence on the long-term behavior of steel truss reinforced continuous rigid frame bridge was discussed.The main works were as follows:(1)Based on a box type concrete beam,the effects of temperature and humidity on shrinkage and creep were discussed.The results show that the influence of temperature and humidity on shrinkage and creep was obvious,and shrinkage was more sensitive to temperature and humidity than creep.Based on the superposition principle,the calculation method of shrinkage and creep under varying temperature and humidity was proposed and verified.(2)A one-year shrinkage and creep test was carried out in the standard environment of laboratory and outdoor natural environment.Using the calculation method of shrinkage and creep with varying temperature and humidity,the coefficient of corrections of creep coefficient and shrinkage strain were fitted according to the short-term test results.By modifying the CEB-FIP(1990)model,a shrinkage and creep correction model considering the effects of changing temperature and humidity was obtained,which could more accurately predict the long-term behavior of the actual bridge.(3)Based on the modified model of shrinkage and creep with variable temperature and humidity,the vertical deformation of the bridge was calculated by using the finite element software,and compared with the field measurement results.The results demonstrated that the modified model was accurate enough.The long-term deformation,stress and loss of prestress of steel truss-stiffened continuous rigid frame bridge in natural environment were analyzed.The effects of temperature,humidity and loading age on shrinkage and creep effects were explored.(4)The influence of steel truss on the long-term behavior of continuous rigid frame bridge was analyzed systematically.The results showed that the steel truss had obvious effect on improving the overall rigidity of the bridge.The analytical formulas of the jacking force under different closure sequences were derived,which could be used to determine the jacking force in practical engineering.The effects of different closure order and jacking force on the deformation and stress of the bridge were discussed.It was recommended to adopt the closure sequence of first side span and then middle span,and applied reverse thrusting force,which could effectively reduce the deformation of the bridge and improve the stress of the pier.