| The construction method of cable hoisting is mainly used in most bridges over rivers and canyons because of its unique advantages.At present,single-span cable hoisting is commonly used,and only one span is used for hoisting.But sometimes because of the limited site and height or the tight construction period,the single span cable crane can not complete the whole bridge lifting work or meet the requirements of the construction period,so the whole construction can be completed by multi-span cable crane.The difference of the structure of multi-span cable crane mainly lies in the main cable,because of the increase of the span,the main cable can be long in the whole structure system,and can also be disconnected and consolidated at the top of the saddle.At the same time,because the multi-span cable crane can lift many spans by itself,it can realize multi-span simultaneous operation.Compared with the single-span cable crane,the construction speed is faster,but the force is more complex,and in the multi-span cable crane,because the tower position is different,there are also some differences in the mechanical characteristics.At the same time,multi-span cable crane and single-span biggest difference,it can achieve multi-span simultaneously lifting,rapid completion of the entire project lifting work.Taking the fourth bridge of Xi River in Wuzhou,Guangxi as an example,the construction method is three-span cable crane construction.Through the research on the key construction technology and structure optimization of multi-span cable crane,this paper provides useful reference for the design and construction of multi-span cable crane in the future,the main research contents are as follows:(1)multi-span cable crane can be divided into two cases according to the main cable structure,one is the main cable in the overall length of the cable crane system,the other is the main cable in the top saddle of the consolidation.Because of the difference between the main cable and the Cable Saddle,the Mechanical Properties of the two structures are not the same.In this paper,finite element software Midas/Civil is used to analyze the load-bearing capacity of the whole bridge hoisting model.The results show that,no matter where the hoisting load is,the stress of the main cable through-length structure on the SOTTA column and the Crossbeam of the cable saddle is less than that of the main cable,and the displacement of the main cable through-length tower is much less than that of the main cable.In the process of Load Position Change,the mechanical performance of the pylons of main cable length is more stable,and there is no sudden change because of the load position change,and the forces on the saddle beams and pylons are more uniform,which is convenient for design.(2)because of the existence of multi-span cable crane with multi-span,whether the force and displacement of SOTTA will change greatly due to the change of stiffness of other span cable towers during the design optimization of the cable crane;In this paper,by constantly changing the stiffness of the side tower and the Middle Tower,the hoisting calculation and analysis are carried out.The results show that the change of stiffness of the side tower or the Middle Tower does not change the mechanical behavior of other pylons,at the same time,the force effect caused by the change of stiffness is not transmitted to other pylons through the main cable but to the pylons connected by the ventilation cable.Therefore,the optimized design does not take into account the impact of the optimized tower on the rest of SOTTA.(3)The biggest difference between multi-span cable crane and single-span cable crane is that multi-span cable crane can be lifted at the same time.The results show that when both sides of the pylon are lifted,the displacement of the top of the pylon is the smallest,and the load of one span,however,moves,has little influence on the other spans which are not lifted and are being lifted,other cross-effects can therefore be ignored at design time.(4)in order to solve the problem of how to continue the hoisting operation from one span to another when the single span cable crane is used,the saddle structure is optimized to ensure the hoisting operation.At the same time,the balance system of multi-span cable crane is more complicated than single-span cable crane.The results show that the multi-tower ventilation cable can ensure the displacement of the top of the tower,but the tension is greater than that of the two towers. |
