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Can the use of temporary nose in incremental launching method reduce the cantilever moment of superstructure to the value of inner support moment?


Temporary nose used to reduce the cantilever moment, that arises from the nature of incremental launching of the superstructure, the temporary nose will be attached to the superstructure front temporary nose and the length of the temporary nose usually is 0.60-0.65 of bridge span length, central prestressing used in conjunction with temporary nose to reduce tensile stresses on concrete during the launching.

Figure 1









The bending moment due to self-weight of the long bridge with equal spans at piers=-0.0883WL^2 and bending moment at the mid-span equal 0.0417WL^2. where W is the unit weight of superstructure and L is the length of spa), without using temporary nose the bending moment at the lead pier could reach to a value of -0.5WL^2, theoretically the cantilever bending moment can be reduced to internal support bending moment by using very long temporary nose, the using of this huge nose will not be economical and practical at fields, therefore we use temporary nose with central prestressing to reduce the tensile stresses on structure to acceptable value.




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