Laboratory Testing of Low-Volume Road Bridge Alternative

In Iowa there are over 20,000 bridges on the secondary road system. The majority of these bridges are under the jurisdiction of county engineers with limited budgets; therefore many county engineers design and construct their own short-span bridges with their own labor force. The objective of this research is to perform laboratory testing on a bridge alternative that counties can design and construct. This concept involves the fabrication of precast units composed of two steel beams connected by a thin concrete deck. The concrete deck thickness is limited so that the units can be fabricated at one location and then transported to the bridge site. The number of units required is obviously a function of the width of bridge desired. After the precast units have been connected, an additional concrete deck is placed. The concrete surface of the units is scarified so that the two layers of concrete are bonded together, thus providing the required deck thickness. Since this bridge replacement system is primarily intended for use on low-volume roads, the precast units could be constructed with new or used steel beams. The laboratory testing program consisted of a series of small-scale tests on different types of precast deck connections, “handling strength” tests of the precast units, a series of tests on the model bridge with only the precast portion of the deck in place, and a series of tests on the fully constructed model bridge. For the bridge model tested [L = 9750 mm (32 ft), W = 6400 mm (21 ft)], five precast connectors gave the desired lateral load distribution; the addition of the cast-in-place deck significantly improved the load distribution characteristics of the bridge system. The units developed and tested result in a simple-span bridge for low-volume roads that is relatively easy to construct.