Analysis On Secondary Internal Force Of Simply Supported-to-Continuous PC Continuous Beam

The simply supported-to-continuous PC continuous beam is one of the widely used bridge structure forms for medium span prestressed concrete continuous beam bridges.Due to the system transformation during the construction process,the secondary internal force of the simply supported-to-continuous PC continuous beam bridge under the influence of concrete creep,foundation settlement,sunshine gradient temperature and late prestress is a problem that must be considered in the design calculation.However,at present,the research on the secondary internal force of the simply supported-to-continuous PC continuous beam is not enough,especially the research on the influence of concrete creep during the foundation settlement process is rare.Therefore,the study of the secondary internal force about the simply supported-to-continuous PC continuous beam bridge still has important practical significance.In this paper,the four-span prestressed concrete continuous girder bridge of Xianhe Bridge is used as the engineering background,and the calculation of the secondary internal force of the continuous beam and its distribution law are studied.The research on secondary internal force about creep and the creeping influce on the foundation settlement is the keynote.The specific research contents and related results are as follows.(1)Using the Dischinger method and the age-adjusted effective modulus method,the creeping secondary internal force of the simply supported-to-continuous PC continuous beam is calculated and analyzed.The comparison results show that the Dischinger method is not suitable for creeping analysis because that the creep coefficient prediction mode expressed by Dischinger formula has a large deviation from the currently applied creep coefficient prediction mode.(2)A comparative analysis of several commonly used creep coefficient prediction models shows that the coefficient of creep coefficient calculated by using the Zhong Jiao 04 model is the closest to that of the Model Code 2010 model.The creep coefficient curve calculated by CEB-FIP 1990 model is slightly.Compared with the former two,the creep coefficient curve calculated by using the China Railway 05 model and the China Railway 17 model is much higher than the creep coefficient curve calculated using the Zhong Jiao 04 model.(3)Based on the classical foundation settlement theory,the basic settlement internal force formula considering multiple factors is established,and the calculation results are compared with the finite element software results,which shows that the established formula is reasonable.(4)When the foundation slowly settles,the factor that has the greatest influence on the secondary settlement internal force is the final settlement of the foundation,which is proportional to the final settlement secondary force after considering the creep effect;secondly,the basic settlement age and system conversion age also have effect to the secondary settlement internal force,and the influence of the two on the final settlement secondary internal force accounts for less than 50% of the elastic internal force caused by the same foundation settlement;finally,the basic settlement rate has the least influence on the final settlement secondary internal force,and its influence on the final settlement secondary internal force is small.However,it has a great influence on the growth rate of the settlement internal force.(5)Under the condition that the system conversion age and the foundation settlement age are both earlier,the creeping internal force caused by the slow foundation settlement is about 45%~55% of the elastic internal force,and the creeping internal force caused by the instantaneous foundation settlement is about 70%~80% of the elastic internal force,so the creeping internal force caused by the slow foundation settlement is about 0.7 times of the creeping secondary internal force caused by the instantaneous instantaneous settlement.The instantaneous settlement secondary internal force considering the creep effect accounts for about the slow settlement secondary internal force.1/3~1/2(this value tends to 1/3 as the settlement age increases).(6)Taking the section at the fulcrum as an example,in the composition of the final secondary internal force,the largest proportion is the prestressed secondary internal force,which can almost offset the elastic internal force at the side fulcrum caused by the entire second-stage dead load;The positive internal force reached 60.4% of the elastic internal force caused by the second-stage dead load;again the creeping secondary internal force caused by the self-weight of the superstructure and the pre-stress,which accounted for 29.7% of the elastic internal force caused by the second-stage dead load;The base is the secondary internal force,The lowest specific gravity is the foundation settlement secondary internal force.Among them,the base slow settlement secondary internal force accounts for 5.7% of the elastic internal force caused by the second-stage dead load,and the base instantaneous settlement secondary internal force accounts for 3.1% of the elastic internal force caused by the second-stage dead load.