When the superstructure is pushed forward, a temporary nose is usually adopted at the front end of the superstructure to reduce the cantilever moment for which the central prestress is designed. The length of temporary nose is about 60-65% of bridge span.
The bending moment of self-weight for internal spans (equal span) of long bridge is -0.0833WL2
at piers and +0.0417W L2 at mid-span (W = unit weight of deck and L = span length). However, without the use of temporary nose, the bending moment in the leading pier when the deck has to cantilever from one pier to another would be -0.5WL2, which is 6 times higher than normal values at support.