Longterm sensor-based monitoring of an LRFD designed steel girder bridge

The new AASHTO LRFD bridge design specifications allow the use of the arching action mechanism in concrete slabs to design lightweight bridge decks. The Star City Bridge in Morgantown, WV is designed according to the LRFD code and measures 306 m over 4 spans. In an effort to demonstrate the long-term performance of in-service light-weight bridge decks, the bridge was heavily instrumented with over 700 sensors that record the response of main superstructure elements to various loading parameters. Data are being recorded every 20 min and provide continuous monitoring and evaluation of the performance of the bridge since construction in 2003–2004. This paper describes the instrumentation system installed on the Star City Bridge and demonstrates the performance of the steel superstructure over 4 years from the time of deck pouring. The expansion and contraction of the superstructure at one end contributed to the relief of environmentally induced internal stresses in the longitudinal direction. Bearing movement constrains on the other end introduced normal forces in the steel girders that are not taken into consideration in deck designs. Straining action variations due to environmental loading amounted to 20% of their initial values after pouring the deck. Temperature data shows development of a non-linear gradient across the bridge width, which explains an additional build-up of stresses found on diaphragm members at the outside girders. Compared to the LRFD specifications, the measured maximum positive temperature gradient across the bridge superstructure was found to have close values, while the maximum negative temperature gradient recorded a higher profile.