Highway improvements drive UH engineering efforts in bridge design

08/02/05

Researchers work to increase efficiency and economy of Texas bridges

HOUSTON, Aug. 2, 2005 A way to build steel bridges cheaper and quicker has been developed by engineers at the University of Houston.

Associate Professor Todd Helwig and Assistant Professor Reagan Herman, both in the Department of Civil and Environmental Engineering at UH's Cullen College of Engineering, collaborated on a project to develop new, more effective and less expensive bridge construction methodology. Helwig and Herman were awarded a Top Research Innovation award from the Texas Department of Transportation (TxDOT). Each year, TxDOT selects top research innovations based on anticipated or already realized dividends to TxDOT and the state. These dividends may be in terms of saved lives, more efficient operations, improved services or financial savings. In addition to the recognition of this research by TxDOT, a paper written by Ozgur Egilmez, a graduate research assistant on the project, earned Helwig and Herman the Vinnakota Award from the Structural Stability Research Council (SSRC).

"The main drive for the project was to achieve better economy during both construction and over the life of steel I-girder bridges," Herman said. "The results of the research study, which enable utilization of permanent metal deck forms for bracing, will facilitate easier bridge inspections and generate fewer ongoing maintenance concerns."

Laboratory tests were conducted in the UH Department of Civil and Environmental Engineering Structural Research Laboratory, with full-scale experimental investigations conducted with a variety of girder cross sections and bracing layouts utilizing a 50-foot long test setup. The research work will be put into practice this fall in the construction of bridges used in the renovation of the Fulton and Irvington overpasses on Loop 610 in north Houston. The current overpass bridges will be removed, and metal deck forms will be used for bracing in the construction of the replacement bridges. Construction of the implementation bridges will be monitored by UH.

Addressing not just bridges in the city of Houston, but those across the state of Texas, the research idea came from initial collaborations between Helwig, Herman and TxDOT engineers. The key with this work is that the research enables an existing bridge element metal deck forms to be used to brace the bridge girders during construction. The research work has generated a modified connection detail that enables the deck forms currently being used to do double duty as both a form for the wet concrete deck and a brace to the steel bridge girders.

In the past, design engineers typically have used cross frames to brace bridge girders during construction. Cross frames are conventional bracing systems that are used to prevent twist of a bridge's girder cross section and are specifically used on the bridge to maintain stability of the bridge girders during construction. According to Helwig, this type of framing is expensive and there can be long-term problems associated with their use, such as fatigue and added cost and length of inspections throughout the life of the bridge. Cross frames also are expensive to fabricate and require heavy machinery to install.

The UH research proposes that permanent metal deck forms that are already used in bridge construction to hold the wet concrete in place as it cures can be used for stability bracing, thereby eliminating a number of cross frames from the bridge. By using an element of the bridge that is already in place, the cost of these bridges is lowered significantly, without reducing their stability.

While cross frames will still be required at all support locations and some intermediate locations, using the permanent metal deck forms for bracing will allow elimination of approximately half of all intermediate cross frames. Although permanent metal deck forms are currently used in the bridge industry to hold the weight of the wet concrete deck during construction, they are not currently relied upon for bracing. The connection details developed at UH allow the metal deck forms to be used to provide bracing for the bridge girders, thus lessening the demand for cross frames on the bridge.

"This simple method can dramatically improve the bracing," Helwig said. "The implementation project on Loop 610 where TxDOT is using metal deck forms as bracing is the first time they've been relied on and have eliminated 340 cross frames on the implementation bridges, saving more than $200,000. One application of this work has almost paid for the research, so it's been money well spent."

Source: Eurekalert & others

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