A study was conducted to determine the structural and economic benefits of using high-strength (6, 000 to 12, 000 psi) concrete in boxbeams for highway bridges. The goal was to establish a range of application of various beam designs in terms of span capacity. The study focused on long-span, simply supported, prestressed concrete box beams. The application of high-strength concrete was investigated in two ways. First, high-strength concrete was substituted for normal-strength concrete in the design of standard beam sections. Second, toimprove structural performance, modifications were made to the geometry of the standard beams in conjunction with use of the high-strength material. In both cases a parametric study was performed to identify the most structurally efficient designs. Results indicate that the maximum attainable span of the box beam can be significantly increased by using high-strength concrete in conjunction with a modified internal void shape. In addition, attainable span lengths were generally longer and had 1/2-in. Rather than 0.6-In. Strands for the beam sections studied. Those designs found to provide the greatest structural benefit were subsequently examined for their relative cost-effectiveness. Coparisons were made on the basis of a total superstructure cost per square foot of bridge deck. For shorter span lengths, spread box beams 3 ft wide were found to be the most cost-effective. For longer spans, the 4-ft-wide adjacent box sections were less costly. Strand size does not appear to significantly influence the cost of a box beam. This paper appears in transportation research record no. 1275, Bridge research 1990.
Abstract