Effect Of Stress And Deformation On Tension Control Of Super Long Prestress Bar For Continuous Rigid Frame Bridges

With the continuous development of modern construction technology,the span of continuous rigid frame bridges is also increasing.If the elevation control of each beam section in the cantilever construction stage is not in place,it will cause a series of engineering problems: the main beam is not linear,the Collapse segment Excessive elevation difference between the two ends is difficult to close;the deviation of the beam section elevation affects the thickness of the deck pavement layer,especially for the continuous rigid frame bridge with the leveling layer removed,reducing the normal service life of the bridge.The linear control of large-span continuous rigid frame bridges is mainly reflected in two aspects: one is to give each beam a pre-cavity for construction;the other is the prestressed steel beam tensile force and tensile load time,which directly affects the latter Construction pre-camber and main beam stress.In engineering,steel bundles with a length of more than 60 m are usually called super-long bundles.However,the current "Technical Specifications for Construction of Highway Bridges and Culverts" does not specify the load holding time of general beams and super-long beams,but only specifies3-5 minutes,which often results in insufficient effective pre-stress of ultra-long prestressed steel beams.To this end,this article relies on the Mabianhe No.2 Bridge under construction to study the effect of extra-long steel beams on the stress and deflection of the main beam during tension:(1)Establish MIDAS / Civil simulation model of Mabianhe No.2 Bridge,analyze the relationship between prestress loss and box beam deflection and cross-section stress during tensioning of the steel beam,and find out that the main beam deflection and cross-section stress influences are more significant Prestressed steel bundle.(2)Carry out analysis of the influence of pipeline friction resistance and pipeline deviation coefficient.By changing the friction coefficient of the prestressed steel bundle in the simulation model,the influence of the friction coefficient u and the pipe deviation coefficient k of the prestressed steel bundle on the stress and deflection of the main beam is analyzed.(3)Carry out field test research on the effect of the ultra-long prestressed steel beam holding time on the deflection and stress of the main beam,select three types of ultra-long steel beams of 79 m,98m,and 139 m,and carry out effective prestress tests under different loading times,combined with the site Collect the stress of the main beam,the deflection of the beam end and the elongation of the steel beam,and use the inversion method to establish the relationship between the holding time of the steel beam and the effective stress,and propose a reasonable holding time of the steel beam of different lengths.The results of the study show that for prestressed steel bundles of different lengths,it is reasonable to control the tension loading time according to the length of the steel bundle in 5min ～ 15 min.The measured results show that the beam deformation after prestressing is in good agreement with the theoretical value,and the maximum error can be controlled within 4mm.The research results of this paper can provide reference for the construction of the same type of bridge.