The American Council of Engineering Cos. of Michigan (ACEC) and the Michigan Society of Professional Engineers (MSPE) presented the annual Engineering and Surveying Excellence Awards on Feb. 25 at the Henry Ford Museum in Dearborn, Mich. The I-94 Modified Tied-Arch Bridge designed by Alfred Benesch & Co. in Detroit received Honorable Award recognition.
The structure is a single-span inclined through arch. The interior and exterior arch ribs are inclined 25° towards each other. The inclination is limited to 25° in order to maintain the desirable vertical clearance, and the ribs are braced together using five football shape braces. The bases of the exterior arch ribs are located at Telegraph Road, while the bases of the interior arch ribs are located at I-94 level. The arch ribs are restrained longitudinally by a reinforced concrete foundation ties that are located four feet below Telegraph Road roadway. The exterior arch ribs are restrained transversely by a short reinforced concrete foundation ties that are located below ground level and tie the exterior arch rib foundations to the abutment foundation.
This is the first modified tied arch with its longitudinal ties buried under the road. It is also one of the few arches with unequal rise. The modified tied arch concept solves the redundancy issue with a tied arch bridge, and also eliminates the requirement of a good soil condition required for a true arch bridge with a foundation system that is independent of the soil condition at the bridge site. The design of the bridge sets some new records that will be followed by others in the near future.
Benesch was responsible for the design of the twin bridges and provided construction assistance services throughout fabrication and construction.
Geotechnical investigation was performed by SOMAT Engineering Inc. and peer review was performed by URS Corp.
The I-94 Modified Tied-Arch Bridges is a response to the efforts of the Detroit Regional Gateway Advisory Council to revitalize Detroit’s economy. The local business community and other parts of the private sector have given their support to enhance the I-94 corridor. With visitors from all over the world coming to Detroit, this structure at the gateway to the Detroit Metro Airport will function as a landmark to the city.
For motorists on I-94, the 72-ft wide structure allows a future fourth lane to be constructed with minimal impact to traffic. For motorists on Telegraph Road, the change from the existing four-span bridges to a single-span bridge improves the aesthetics and driver comfort with a clear sight distance.