A Study of Girder Deflections During Bridge Deck Construction: Final Report

About the report:

Problems involved in obtaining the desired thickness of bridge decks were investigated. The study, which was limited to decks which were longitudinally screeded during construction, included (1) field measurements of the girder deflections during construction, and (2) a theoretical frame analysis of the girder deflections under the field loading conditions. Each of the two spans investigated were simply supported steel plate girder designs. When full span length longitudinal screeding is used, the finished grade elevations are set on the screeding edge of the machine and remain independent of the bridge girder deflections during deck placement. Consequently, any factor affecting the girder deflections, and thus the forming elevations, will, in turn have bearing on the final thickness of a bridge deck. In addition, all factors which, in effect, cause the deck forming to be too high at the time the concrete is screeded to grade have the potential of causing a shy deck thickness. The most significant factors were found to be: (1) Plan dead load deflection values which are in error, (2) the differential temperatures existing between the top and bottom flanges of the girders during concrete placement as opposed to those that may have existed when the forming elevations were established, and (3) the transverse position of the concrete dead loading at the time a final screeding pass is made over a given point on a span. Based on the results of the study, certain recommendations are offered regarding the computation of dead load deflections and precautions to be observed during construction when longitudinal screeding of the concrete deck is used.

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