Research Of Construction Control Of Continuous Beam Bridge Under Different Time Limit

The actual force and deformation state of long-span prestressed concrete continuous girder bridge which in cantilever casting are difficult to accord with the design state because of the long construction period and the large span and the external environment is complicated and changing.In order to ensure that the linear and internal forces of the bridge structure meet the design requirements,it is imperative to take reasonable construction control measures for analyzing the stress and deformation state of the beam.To find the reason about the possible deviations between theoretical values and real values,and put forward the measures timely to correct the deviation,and guide the construction.This article took the special bridge of YangZhiShui as an engineering example,and the construction technology of prestressed concrete continuous control girder bridge under the time difference of construction was studied.The main work and conclusions are as follows:(1)The finite element model of the full bridge was established by Midas/Civil,and the deformation and stress of the main girder were analyzed.The camber and the formwork elevation of each section are determined;(2)The linear and stress monitoring of the beam were carried out.The theoretical and measured values of each construction stage were compared and analyzed to ensure the safety and reliability of the construction process.Finally,the bridge state met the design requirements.The theoretical displacement value and the measured displacement value of each construction stage were in good agreement with less than 1.5 cm.Within the allowable error range,the measured stress were in accordance with the specification requirements;(3)Under the effect of the difference construction period,the influence of the time difference of construction on the displacement of the beam is mainly caused by the time-dependent factors.Therefore,it is necessary to analyze the shrinkage and creep of concrete and the long-term prestress loss caused by the concrete creep and the relaxation of the steel.Analyzed these parameters to influence the displacement and stress of the beam for better guidance on site construction control.The displacement of the beam in cantilever state and closure by one after another span,with the time difference of construction was bigger,the deformation of concrete creep and shrinkage produced larger deformation,and the prestressed produced more small deformation.With the increase of time difference of construction,the maximum stress at the zero block of the beam decreased gradually.The maximum stress produced by the prestressed steel bars was gradually reduced,and the maximum stress caused by the creep and shrinkage of the concrete increased.10 years after the bridge completion,the difference of time limit has no effect on the displacement and stress of the beam.(4)In consideration of and do not consider the time difference of construction,the effect of stress and displacement of girder under different closure sequences were analyzed.In the continuous beam closure scheme analysis,consider and do not consider the time difference of construction has little effect on the displacement and stress of beam,and also on closure scheme selection.The best closure scheme selection should be combined with the actual theory,according to the site construction and duration and other factors to be considered.