Shortening the Critical Path in the Construction of Concrete Viaducts

摘要

There are two typical environmentally friendly "in situ" construction methods for building mediumspanrnlong concrete viaducts: span by span construction with travelling scaffolding and launchingrnmethod. Both ways share one important characteristic; the deck can be constructed independentlyrnfrom the valley they are bridging. This is why, sometimes, these construction procedures arernimposed by the owner whereas other economical procedures, such as the use of precast concreternbeams, are strictly forbidden. Concreting of span by span construction with travelling scaffolding isrntypically made in two phases. In the first phase, webs and bottom flange of the box girder arernconcreted. In the second phase, top flange is concreted. Once the cross section is self-supporting,rnthis is to say, once the concrete of the top flange is hardened, the segment can be prestressed and thernscaffolding can be shifted to the next span. This procedure takes usually two weeks per span. Inrnorder to shorten the critical path, it would be advisable to look for self-supporting cross sectionsrnafter the concreting of the first phase, prestressing and shifting the scaffolding subsequently andrnpouring the second phase out of the critical path. First phase would include the concreting of webs,rnbottom flange and the overhung top flanges. The trade-off of this procedure will imply somernstructural problems to be studied, such are the connection between different phases and therntransverse bending moments to appear until the cross section is closed. The paper will provide anrninsight into the modification of the traditional construction methods and into the associatedrnstructural problems and potential solutions.