Nose-Deck Interaction in Launched Prestressed Concrete Bridges

Abstract

Incremental launching is a competitive construction method for medium-span prestressed concrete bridges. Compared with the other techniques for in situ casting, in short bridges it is an alternative to the use of falseworks and reduces the cost of labor with the same investment. In longer bridges it is an alternative to self-launching centering and reduces investment with the same cost of labor. Compared with segmental precasting, it may reduce both investment and the cost of prestressing. The design of a launched bridge is affected by temporary stresses arising from its movement over fixed bearings. These stresses tend to increase the cost of materials, reducing the competitiveness of the construction method. Of the various devices used to reduce temporary stresses, adopting a launching nose has virtually become standard, permitting an effective control at competitive costs. The techniques of optimizing the nose-deck interaction are illustrated here through several graphs, and the analysis of special cases may be carried out by means of an ordinary spreadsheet.