Incremental Launching Force Analysis And Research On Key Problems Of Double-layer PC Box Girder Bridge

The incremental launching method in,the construction of PC bridge in our country is very extensive,PC box girder concrete incremental launching method has formed a set of relatively perfect theory in various aspects after the past few decades'development.But the domestic research about double layer PC box girder incremental launching is still a minority.Because of the asymmetry of the cross-section form,the biggest characteristic of double layer PC box girder is that the cross section does not around on both sides of the temporary track center line,so its force has significant difference with the symmetrical box girder.Taking the sixth Liuyang River Bridge double layer PC box girder incremental launching as the engineering background,studying the stress characteristics and construction control technology of the double layer PC box girder,some useful conclusions are obtained,which have important theoretical significance and engineering application value.The main contents of this paper include the following:1)Using MIDAS/civil 2012 software to establish a full-bridge finite element model of the whole incremental launching construction,the change law of the main variables such as the internal force,the supporting force of the girder and the deflection of the guide beam during the incremental launching are obtained,which provided numerical reference for the construction control.2)The construction state and the bridge state of incremental launching bridge have great differences in the stress,prestressed has to meet the requirements of the bridge state and the requirements of construction state,but it is often limited by the size of the cross section.Therefore,it is necessary to optimize the PC box girder with prestressed concrete beam.Now taking the sixth Liuyang River Bridge prestressed concrete girder as an example,some measures to optimize the stress of bridge are put forward,which has certain reference value for the same type of bridge prestress.3)It is impossible to avoid the alignment of the box girder during incremental launching.Especially for double PC box girder,section centroid is not on the left and the right slide center line,so left and right slideway anti force have a bigger difference which results more serious box girder deflection problem.The two methods of weighting and changing the direction of traction force in the horizontal plane areput forward to solve the phenomenon of deviation.The formula derivation of these two methods is carried out and numerical analysis is carried out according to the weighting effect;On this basis,a new type of limiting and rectifying device is put forward according to the form of double layer PC box girder cross section.4)In the process of incremental launching,the pier will carry out a certain horizontal force,so checking calculation of bearing capacity is a necessary factor to guarantee the construction safety.In this paper,simulation analysis model of the overall lower support piers and steel structures is established and the influence of the friction coefficient and the force on the bearing capacity of the lower structure is studied.The effect of the pull cable is studied,which shows that this method is very practical.5)The application of "double layer"cross section in the incremental launching is less,lack of relevant construction experience and technical summary,so according to the construction control of the sixth Liuyang River bridge,the stress and deformation of the structure and the key technology of the construction are studied,which can ensure the safety of the structure and the smooth construction,which provides experience summary for the construction of the same type of double deck box girder.