incremental launching method

(1)The bending rigidity of launching nose and main span (EnIn, EIrespectively), dead weight and load intensity (qn, q) are constant.
(2)Each span length is l; the length of launching nose is ln.
The main span and the launching nose in the process of incremental launching can be regarded as multi-span continuous beam. Calculation methods consist of analytic method and finite element method based on force method (continuous beam three momentequations). Using this equation Jixiang Zhou has found out some numerical solutions in several sections whereas he cannot provide general analytic solutions.Many engineers have announcedtheir analytic solutions which howeverlack for precise evidences.This paper introduces the equal-span three moment equation of continuous beam. According to arrays and limitation methods, this paper illustrates the analytic solutions ofbending moment and reaction of supports in the cross section of continuous beam as well as reasonable launching nose parameters. As a result, the control inner force can be found.
(3)Without regard of any other load except theself-weightof launching nose and main span.
(4)Without regard of the shrinkage and creep of concrete and support settlement, calculate by lowering the framework once only.
Define the incremental launching process by x, which is the distance between the front-end of the main span and the second support (n, n 2). According to the features ofincremental launching stress, separate the process into two phases: firstly, from the front-end of main span leaving out of support n (x=0) to maximalcantilever point (x=l-ln), now the launching nose reaches the first support while this support is out of work, so n. In the figure 1, the left side of support 0 is platform area, where the next is the same.
Asthe incremental launching span grows, in the front region of the main spanthe hogging moment of the support (reinforcedcontinuous concrete beam) or the reaction of supports (continuous steel box girder)are the factors which control the incremental launching. In order to reduce the hogging moment or the reaction of supports the safest, swiftest and the most economical way is to connect the front region of main span with a launching nose.
1 Launching nose –main span theoretical model
1.1Basic suppose and phase division
In general case, the contiቤተ መጻሕፍቲ ባይዱuous beam applied to incremental launching method possesses these features: equal cross section, multi-span, equalspan (or equal span at the inner spans butless at the outer spans). In order to simplify the calculation, the basic supposes of launching nose-main span theoretical modelare the following:
Method for Determination of Reasonable Parameters of Launching Nose for Continuous Beam
Abstract
According to the common characteristics of continuous beam built byincrementallaunching method, including constant cross-section and equal span (or equal span at the inner spans but less at the outer spans), using three-moment equations based on thethinkingof lowering the formwork once only and force method, by means of sequence of number and its limit, theexpressionsof bending moments atthe twoouter supports and the uniformly distributed dead load of the deck during the incremental launching were formula of the reasonable length of the launching nose was deducted. It was gained by means of numerical analysis that the reasonable ratio of the flexural stiffness of the nose to that of the deck is 0.2. Furthermore, thecontrolinternal forces were presented when nose parameters were bining some practical projects, the common structural types and design principles were explained.
Keywords: bridge engineering; continuous beam; three-moment equation; reasonable parameters of launching nose; incremental launching method
Withreinforcedmaterial(such assteel stranded wire), low-friction-resistance material(Teflonboard andrustless steel plate),incrementallaunchingdevice(such as jack and continuous jack)and computer simulation technology develops,incremental launching methodconstruction technology increasingly matureand the prospect ofitsapplication is turning more comprehensive.For instance,the Millau Bridge in France completed and opened to traffic in 2004, whosetotalspanis setas204 m+ 6 x 342 m + 204 m; the main span was constructed using the incremental launching method. In addition, the launching span is 171 m which is the top technique in the world. Furthermore,Zhenzhou Yellow River combined bridge in the Shi-Wu line is being constructed. The total span is projected as 120 m + 6 x 168 m + 120m with the launching span of 168 m, which has dramatically enhanced the level of incremental launching technology in China.