Method for Determination of Reasonable Parameters of Launching Nose for Continuous Beam

According to the common characteristics of continuous beam built by incremental launching 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 the thinking of lowering the formwork once only and force method,by means of sequence of number and its limit,the expressions of bending moments at the inner supports for continuous beam during two phases of incremental launching process were educed.Based on these results,the evolutions of bending moments at the inner supports of continuous beam with the moments at the two outer supports and the uniformly distributed dead load of the deck during incremental launching were discussed and disclosed.On the principle of minimum bending moment of the deck at the front support,the 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,the control internal forces were presented when nose parameters were reasonable.Combining some practical projects,the common structural types and design principles were explained.