Summary:

A unique network tied-arch bridge with free-standing arches was designed to carry 2nd Avenue traffic over Interstate (I-94) in Detroit, Michigan. This 245-ft-long, 96.5-ft-wide bridge, skewed at 18 degrees, is the first skewed, unbraced network arch bridge constructed in the United States. The superstructure frame was erected off-site at a bridge staging area and subsequently transported and placed over the I-94 freeway using self-propelled modular transporters and a lateral launching technique to complete construction. Based on observations from analytical models and discussions with the Engineer of Record (EOR), the peer review engineer, and the Michigan Department of Transportation (MDOT), an instrumentation system consisting of 112 vibrating wire sensors was designed to: (i) monitor strains in major structural components during construction to establish post-construction stress states; (ii) track strain changes during the service life to support bridge maintenance and load rating decisions; and (iii) collect sufficient data to verify key design assumptions. Of these sensors, 96 were embedded in the concrete during construction, and 16 were mounted on the hangers after erection of the arches and hangers. This instrumentation strategy enabled continuous monitoring of strains in the concrete frame and forces in the hangers, providing a clear understanding of the structural behavior throughout construction. The collection of a little more than two years of post-construction monitoring data provided valuable insight into the bridge’s behavior under service conditions. Analysis of the monitoring data demonstrates that the structure is performing within established design limits, thereby increasing confidence in the implementation of innovative structural systems and complex construction methods that minimize traffic disruption and enhance safety. Load testing results indicate that the bridge exhibits minimal sensitivity to live loads, with seasonal temperature variations governing the stresses developed in the structure. A fully functional monitoring system, along with operational stress limits for each instrumented location, was delivered to MDOT. This system enables continuous, data-driven monitoring of the bridge, facilitating timely identification of maintenance, repair, and load rating needs over the long term without reliance solely on traditional visual inspection methods.

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