Study On Long-term Deflection Characteristics And Mechanism Of Multi-span Continuous Rigid Frame Bridge

Multi-span continuous rigid frame bridge are widely used in important traffic arteries such as highways,railways and urban roads.Cracks and deflection are the vital and troublesome problem in the bridge engineering,which normally caused by the dead load and live load during the structural service life.In order to investigate the long-term deflection mechanism of multispan continuous rigid frame bridge,the measured deflection data of a five-span continuous rigid frame bridge are summarized and analyzed firstly.On this basis,the long-term deflection characteristics and mechanism research of multi-span continuous rigid frame bridge are studied systematically.The major achievements are as follows:(1)The existing research and analytical methods about long-term deflection of multi-span continuous rigid frame bridge are summarized.Due to the shortcomings of the current way to investigate the long-term deflection,the subroutine of concrete shrinkage and creep considering the bridge construction process is developed based on the three-dimensional solid element analysis function of ABAQUS software,which can carry out the time-varying effect analysis of the multi-span variable section continuous rigid frame bridge.(2)The growing characteristics of long-term deflection and cracks of a 20-year serviced five-span continuous rigid frame bridge are concluded through the analysis of measured data.The results indicate that the mid-span deflection of the bridge is most severely,the deflection of the secondary side span around the pier is upward and the same results presented at the side span;the amount of cracks on the web are the biggest,followed by the bottom plate and the roof is the lightest.The cracks of web and bottom are mainly distributed between the 1/4～1/2place of each span,and the roof cracks are mainly occurred in the mid-span and the junction of each pouring block place.(3)Using the MIDAS model,aiming at the problem of excessive deflection of the fivespan continuous rigid frame bridge in the long term,the internal force and deformation distribution of the bridge at the completion stage and 20 years after the completion of the bridge were analyzed,and the internal force and deformation distribution characteristics of the bridge under different shrinkage and creep models,different ages and prestress were studied.The results show that the unreasonable internal force distribution at the completion of the bridge is one of the main reasons for the serious long-term deflection of the five-span continuous rigid frame bridge;compared with CEB-FIP(1990)and ACI209 code,the deflection of middle span of "Highway Bridge Regulation" is larger,while the deflection of secondary span and side span is less different;the age has a more obvious influence on the mid-span deformation,and the secondary side span and the side span have little effect;it is more effective to reduce midspan deflection to increase roof prestress than to increase floor prestress.(4)Based on ABAQUS and its subroutine,the time-varying deformation law of threedimensional solid model,the time-varying stress distribution of mid span roof and web,and the time-varying prestress loss law of roof,web and bottom are analyzed,and the influence of prestress relaxation on deformation and prestress loss under fatigue is carried out.The results show that compared with MIDAS model,the calculation results of long-term deflection under spatial effect will increase;The law of prestress loss of roof shows that the later the tensioning stage is,the smaller the prestress loss is,the closer the prestressing tendon is to block 0,and the smaller the prestress loss is;Considering the prestress relaxation under fatigue,the mid span deformation will increase by 15.92%,the mid span deformation of secondary side span will increase by 13%,and the prestress loss of roof and floor will increase by about 4%.(5)In view of the long-term deformation development of the structure under the action of crack coupling,the MATLAB calculation program was developed.By comparing the calculation results of the program and the experimental results of the existing literature,the theoretical method and the program were verified,and the deformation characteristics of the anti-bending point section of the mid-span of the bridge after considering the crack were studied.The results show that the cracking rate is fast within the first 50 days,and gradually eases with time,and the cracking range basically becomes stable after 1000 days.After considering the effect of cracks on the long-term deformation,the deflection of the middle span will increase by about 25%.