Pouring sequence for box girder bridge on flexible truss scaffolding

I would like to thank both Austim & Hariharan for your prompt reply about the above subject.

From a Contractor's perspective, I would look at pouring the bottom flange first, then the webs, and finally the top flange. This way you not only have the falsework supporting the beam, but the bottom flange is distributing the load. On a structure constructed last year in this manner, the bottom flange was PT’d to an initial stress level for added support. The best I recall it was a PB design.

Dear ASDF

Thanks for your Eamil reply. However, can you let me know the span of the bridge and the type of scaffolding for the bridge you were involved with. If you poured in the manner you have described then the "U"section formed by the webs and the bottom flange would have been fairlystiff compared to the supporting flexible scaffolding and some considerable weight of the top flange would have been carried by the bottom falnge. How did the bottom flange and the webs i.e. "U" section carry the stresses due to this weight. Please write me in detail when you find time. Many thanks again.

Bimal 1

This cast in place box girder structure was approximately 1100' in length, and the average span length 225'. The bottom flange averaged 10", and was blistered near the corners for post tensioning ducts. The falsework system consisted of driven pile, supporting a homemade 'mabey' type structure, supporting a combination of timber and steel stringers, and a plywood platform. It sounds stiff, but was only stiff enough to cast the bottom flange.
After curing, the flange being supported by the pile system, became an excellent work platform to form and pour the webs, two internal plus the external, and the top flange, which was placed using a traveling form system. The overhangs were cast using another traveling form system cantilevered from the top flange.
After curing, a considerable amount of post tensioning, both longitudinal and transverse, was completed.
As best I recall, the top flange was 58’, including the 14’ overhang on each side, the bottom flange 22’, and the webs about 9’.