Qualitative Measure of Efficiency of Post-Tensioned Concrete Bridges

This article presents the results of a study of the efficiency of post-tensioned bridges. It is an initial step toward a broader goal of providing designers with a simple and rational basis for assessing the efficiency of bridge design concepts. The approach consisted first of establishing a set of parameters defining the primary characteristics of the bridge type considered, simply supported multiple-T systems. Within a defined range of parameter values, designs were generated and checked by computer against applicable safety and serviceability criteria. A subset of valid cases was extracted with the lowest value of reference depth, defined as the ratio of the cross-sectional area and deck width. Reference depth was used as the primary measure of efficiency because it measures concrete quantity, independent of span or width. The study shows that cross sections with three webs minimize reference depth. For each span length, the range of values for span-to-depth ratio for efficient cross sections is well defined and limited. Minimizing reference depth does not require large quantities of prestressing steel.