| The local stress characteristics of the contact area between wide steel box girder and launching support are lacking research,and the state of local stress is crucial to ensuring the safety and smoothness of the launching process.Walking-Type incremental launching requires higher synchronization control accuracy.For long-span and wide steel box girder launching,proper synchronization control accuracy and strategy is also one of the key technologies of incremental launching.In view of the above situation,taking the launch of curvature vertical curve steel box girder in Tuojiang Fourth Bridge in Luzhou as the background,Research and analysis are carried out in four aspects:The method of determining the elevation adjustment scheme,stress state of the construction process of steel box girder with variable curvature vertical curve,,the local stress state of the lateral four slide track type launching wide steel box girder and the walking-type incremental launching synchronization control strategy.The specific contents are as follows:(1)Based on the finite element model and the calculation method of "once falling frame+ pier moving beam is not moving".,the "single step modulus search and composition method" and "beam adjustment method" are adopted to determine the adjustment scheme of the slideway elevation in the whole process of launching curvature vertical curve steel box girder.the amount of calculation,the amount of adjustment and the stress state of the structure are compared and analyzed,It is further clear that the single step modulus search and composition method is a better method to determine the scheme of support elevation adjustment during girder launching process with vertically varied curvatures.(2)Based on the scheme of support elevation adjustment determined by the single-step modulus and composition method,the stress state of the beam body and the piers and its sensitivity to support elevation adjustment error are analyzed.the results show that(1)In the process of launching of steel box girder,all the stress indexes of the structure do not exceed the limit value,the scheme of support elevation adjustment is feasible,and the whole process of the launching is safe.;(2)The reaction force of the support point is very sensitive to support elevation adjustment,and the adjustment precision of the slide elevation error should be controlled within 5mm.(3)When multiple positions are adjusted at the same time in the adjustment condition,the adjustment of each pivot should be synchronized(such as 1cm a level).(3)A "beam-shell-solid-contact" hybrid finite element model under typical disadvantageous condition was set up by the software ABAQUS,the stress of the steel box girder at the L5 temporary pier with the most disadvantageous local force and its sensitivity to the material parameters and the construction error are analyzed.the results show that(1)the linear elastic local stability coefficient and stress of the steel box girder at the slipway under the typical disadvtageous condition meets the requirments of the specification;(2)In the unstress state,the transverse four slideway has the same elevation on the top surface and the same height at the bottom of the beam,under the self weight effect of steel box girder,the counterforce of transverse four slideway is not equal,the stress distribution of the steel box girder at the slideway is not uniform,and the distribution ratio of the counterforce to the internal and external slideway is 1.69:1;(3)On the condition of the pad adapting the design area,local stress of the steel box girder at the slideway is the best when the pad's equivalent elastic modulus reduced to 60%of the steel;(4)The stress of the main force of the steel box girder at the slideway is sensitive to unsynchronized jacking and rotation error of transverse four slide way;(5)The safety threshold of the vertical jacking height difference is ±5mm,the maximum equivalent stress value of the steel box girder at the slideway is minimum whe the top surface of the outer steel pad is higher than the top of the inner steel pad 2mm;(6)The allowable value of the axis deviation for the incremental launching in?Technical Specification for Construction of Highway Bridge and Culverts?is 10mm,According to the background of the project,the value of the steel box girder launching construction with transverse four slide way can be relaxed to 30mm.(4)In view of the phenomenon of "channeling" in the process of launching the steel box girder and the problem of unsynchronized launching,The force analysis of the pier shows that the oil pressure pulse is related to the swing of the pier top and has nothing to do with the place of the swing.When the amplitude of the imbalance force on the pier top(which is reltated to the difference between the dynamic and static friction force and the oil pressure pulse)and the frequency of the pier are same,the amplitude of the pier top has nothing to do with the mean size of the unbalanced force,but it is related to the amplitude of the unbalance force.In the launching process,the setting of the top thrust of the top of each pier should be balanced with the friction force in each place.Based on the above analysis results and the original pushing strategy,the strategy of step synchronization control is further optimized. |
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