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Report No.: CCEER-11-3

Title: Instrumentation and Monitoring the Galena Creek Bridge

Authors: Vallejera, J. and Sanders, D.

Date: September 2011

Sponsoring Agency: Nevada Department of Transportation (NDOT)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557

Abstract:

The Galena Creek Bridge is a large structure with a unique design for Nevada. To capture and analyze the structure's behavior, a field research project was conducted with two objectives: 1) instrument the southern portion of Galena Creek Bridge's southbound structure, and 2) use analytical models to subdivide total strain measured at the bridge into components of load induced, time-dependent, and temperature‐dependent strains. For the instrumentation plan, 108 instruments, each comprised of a strain gage and thermistor, were placed in seven cross sections in the arch and three cross sections in the deck. These instruments monitored the structure during construction from September 2008 to December 2010.
Three analytical models utilized staged construction, time‐dependent behavior of concrete and global temperature change in the structure to quantify the contribution of load, time-dependent effects, and temperature-dependent

effects on total strain. The analytical results showed temperature contribution to be insignificant in comparison to the contribution of time-dependent effects and load to total strain. Although temperature data from the thermistors gave readings and trends that were similar to the recorded temperatures at Galena Creek Bridge, strains from the bridge varied from the analytical results, from 20% up to 14,733%. Error ratios generally decreased as work progressed along the arch, and may be due to both UNR and the construction crews' familiarity with construction processes on the arch as time progressed. For both the arch and deck strain gages, the large error ratios may be attributed to strain caused by damage to instrumentation or cables during construction, faulty installation of the instrumentation, or the frequent power loss to the data collection system. With large error ratios, separating the temperature, time-dependent effects, and load‐induced strains from the total strain data collected from Galena Creek Bridge was difficult. For future field projects, improvements regarding planning and protection for instrumentation will decrease the contribution of outside variables to total strain, and allow for comparisons between analytical model results and field data.

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