Field Testing Serviceability Performance of Missouri's First High-Performance Steel Bridge

The Missouri Department of Transportation (MoDOT) built the state's first high-performance steel (HPS) bridge in 2002. MoDOT Bridge A6101 uses HPS 70W in the design of the 138-ft–138-ft two-span, five-girder bridge. Design calculations show that using HPS in only the highly stressed regions (hybrid design) led to a superstructure steel weight savings of nearly 17% and an estimated cost savings of approximately 11% compared with building a conventional 50-ksi (50W) bridge. As in many other progressive states, in Missouri the future of HPS is promising. HPS 70W is a superior steel that can lead to more economical bridges than can conventional 50-ksi designs. However, with the higher-strength steel, sections become smaller and deflections increase. Many states, including Missouri, impose deflection serviceability limits that are stricter than those dictated by AASHTO design provisions. The researchers worked with MoDOT to instrument, field test, analyze, and evaluate the performance of completed Bridge A6101. Serviceability field testing confirmed that MoDOT's, and thus many states’, serviceability criteria are conservative compared with those of AASHTO. The conservative serviceability procedures used by some states will cause many HPS designs to be controlled by deflection, as A6101 was, instead of strength parameters. When deflection controls the design, there is no benefit in using higher-strength materials, and the weight and cost savings will not be realized. This paper presents the serviceability testing and serviceability performance of Bridge A6101.