Low-Volume Road Bridge Alternative

Recent reports indicate that a significant number of the nation’s bridges are either structurally deficient or functionally obsolete. A large number of these bridges are on the secondary road system and fall under the jurisdiction of county engineers with limited budgets and engineering staff. In response to this problem, a bridge replacement system was developed for simple span bridges with minimal to no skew that county engineers can design and build with limited resources. The bridge system involves fabrication of precast units consisting of two steel beams connected with a thin reinforced concrete deck. The precast deck thickness is limited to reduce the weight of the units so that they can be fabricated at one site and then easily transported to the bridge site. Multiple units are then connected on site to give the desired width of bridge, after which a reinforced cast-in-place concrete deck is placed over the entire bridge. Development of the design methodology for the steel beam precast unit bridge consisted of four phases. During the initial phase, small-scale bridge components and a full-scale model bridge were constructed and tested in the Iowa State University Structural Engineering Laboratory. These specimens were tested under a variety of loading configurations under service and ultimate loads. After completion of the laboratory testing, finite-element models of the laboratory bridge were developed and validated with data collected during the first phase. The validated finite-element model was then used to extrapolate analyses of common bridge configurations. The results of the analytical investigation were then combined with classic bridge engineering principles into a design methodology that is easy to use and understand. Although it is not discussed in detail, a demonstration project in which this concept was used has recently been completed and tested.