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Monitoring of the Bonnet Carré Spillway Bridge during extreme overload.
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2003-10-01
[PDF-1.34 MB]
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Abstract:This report concerns the monitoring of a portion of the Bonnet Carré Spillway Bridge during an extreme overload. On Tuesday, November 5, 2002, Tulane University was requested to monitor strain at the bottom flange of two adjacent prestressed girders before, during, and after the passing of the overload. On Thursday, November 7, this request was modified to include monitoring of strain in the following regions of interest:
a. Positive moment region on three adjacent girders
b. Negative moment region over the pile cap at the center of the bridge width
c. Positive and negative moment region on one pile cap
d. Shear region on one pile cap
e. Compression region on one square pile
It was originally believed that the overload would cross the bridge at approximately 4:00 a.m. on Saturday morning, November 9. Access in the form of a "Reach-All" vehicle was provided on Friday, November 8, and strain gauges and wires were affixed to appropriate locations of the structure. Due to mechanical difficulties the overload did not pass until approximately 3:00 pm on Sunday, November 10. On Saturday, November 9, access was also provided to the structure, and instrumentation was placed. During the day of Friday, November 8, an additional request was made to monitor the strain on a reinforcing bar in the negative moment region of the concrete deck over a pile cap. Furthermore a request was made to monitor the displacements at midspan of the girders on Saturday, November 9. These strains and displacements were monitored during the passage of the overload. Acoustic emission was monitored on three girders at midspan during the passage of the overload as well. When the overload crossed the bridge on Sunday, November 10, many of the strain gauges were still functional but a few had been lost due to environmental exposure or other factors. Due to the very short notice prior to the monitoring, some compromises were made in the data collection. These included, but were not limited to, the use of a quick curing epoxy for the mounting of the strain gauges, the use of long runs of 18-gauge shielded three-conductor wire from the strain gauges to the data acquisition system, the elimination of weatherproofing in some instances, and the use of portable generators to power the data acquisition system. After the monitoring was performed, efforts were made to quantify and reduce the error that may have arisen from these necessary compromises. These efforts included additional laboratory testing described in this report.
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