Construction and testing of a low volume road bridge alternative: Steel-beam precast units
Date
1999
Authors
Fagen, Matthew Eric
Major Professor
Advisor
Smith, Gary R.
Klaiber, F.W.
Wipf, T.J.
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Abstract
A report published in the November 1998 issue of "Better Roads" stated that 35% of all city, county, and township bridges in the United States are considered structurally deficient or functionally obsolete. In Iowa, approximately 6,600 of the 21,118 such bridges are either structurally deficient or functionally obsolete. Most county budgets are limited, thus the number of bridges that can be replaced during a fiscal year is also limited. The need exists for a less expensive method of design and construction for bridges used on low volume roads. The steel-beam precast unit bridge concept fulfills this need. The steel-beam precast unit bridge requires the fabrication of precast double-tee (PCDT) units, each consisting of two steel beams connected by a reinforced concrete deck. The weight of each PCDT unit is minimized by limiting the deck thickness to four inches.
This allows the units to be constructed off-site (i.e. at a county maintenance shop) and then transported to the bridge site. The number of units required is a function of the width of bridge desired. Once the PCDT units are connected, a cast-in-place (CIP) reinforced concrete deck is placed over the PCDT units and the bridge railing attached. Since the steel-beam PCDT unit bridge design is intended primarily for use on low-volume roads, new or used steel beams could be utilized. This project involved three major divisions of work. The first division involved documenting the fabrication of four precast steel-beam units at an off-site location through photographs, slides, and a video. The second division consisted of transporting the completed units to the bridge site where final construction was completed by an independent contractor. The final division involved the service load testing of the units at different stages of the construction process.
Based upon the construction and service load testing, the steel-beam precast unit bridge was successfully shown to be a viable low volume road bridge alternative. The construction process utilized standard methods resulting in a simple to use system that can be performed with a limited staff. Service load test results indicated adequate strength for all legal loads.
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