A design methodology for a low volume road bridge alternative: steel beam precast units

Recent reports have indicated that 23.5 percent of the nation\u27s highway bridges are structurally deficient and 17.7 percent are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86 percent of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement;In a recent investigation, HR-365 Evaluation of Bridge Replacement Alternatives for the County Bridge System several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69 percent) have the ability and are interested in utilizing their own forces to design and construct short span bridges. In reviewing the results from HR-365, a new bridge replacement concept was developed;This concept involves the fabrication of precast units (two steel beams connected by a concrete slab) by county work forces. Deck thickness is limited so that the units can be fabricated at one site and then transported to the bridge site where they are connected and the remaining portion of the deck placed. Since the bridge is primarily intended for use on low-volume roads, the precast units can be constructed with new or used beams;In the experimental portion of the investigation, there were three types of static load tests: small scale connector tests, handling strength tests, and service and overload tests of a model bridge. Three finite element models for analyzing the bridge in various states of construction were also developed and extrapolated to various bridge configurations;Small scale connector tests were completed to determine the best method of connecting the precast double-T (PCDT) units. Handling strength tests on an individual PCDT unit were performed to determine the strength and behavior of the precast unit in this configuration;The majority of the testing was completed on the model bridge (L = 9,750 mm (32 ft), W = 6,400 mm (21 ft)) which was fabricated using the precast units developed. Some of the variables investigated in the model bridge tests were number of connectors required to connect adjacent precast units, contribution of diaphragms to load distribution, influence of position of diaphragms on bridge strength and load distribution, and effect of cast-in-place portion of deck on load distribution. In addition to the service load tests, the model bridge was also subjected to overload conditions. Using the finite element models developed, one can predict the behavior and strength of bridges similar to the laboratory model as well as design them;Based on the experimental investigation and analytical models that were developed to describe the model bridge behavior, a design methodology for the PCDT bridge has been developed for the bridge superstructure. This design methodology has been programmed in to an easy to use program that allows quick and easy bridge design. A pre-prepared set of plans has also been developed that can be used to construct the PCDT bridge superstructure