Pre-stressed Losses in Decked Bulb-tee Girders

The American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) Bridge Design Specifications provides guidance for the calculation of pre-stress losses in precast concrete beams. Changes (2007) in the AASHTO code results in inconsistent pre-stress loss predictions for decked bulb-tee girders such as those used by the Department. Specifically, the simplified procedure for pre-stress loss prediction results in much less loss than that predicted from the previous versions of the AASHTO codes and are less than that resulting from the "refined" method of the current code. Better design predictions for long-term pre-stress losses may result in longer spans, few girder lines or shallower girders. Saving one girder line would save the Department about $75k per span (~5% of bridge cost) for the typical highway bridge. More accurate per-stress loss values would result in more accurate girder strength predictions.