The Effect of Corrosion and Cracks on the Safety of Steel Bridges

Location

CSU 284

Start Date

21-4-2008 8:00 AM

End Date

21-4-2008 10:00 AM

Student's Major

Mechanical and Civil Engineering

Student's College

Science, Engineering and Technology

Mentor's Name

Karen Chou

Mentor's Department

Mechanical and Civil Engineering

Mentor's College

Science, Engineering and Technology

Description

The motivation behind this research was the recent collapse of the I-35W Bridge in Minneapolis, MN. The purpose of this project was to build models of single-span bridges to examine the change in their deflections due to corrosion and cracks. Four linear variable differential transmitters (LVDTs) were carefully calibrated and used to measure the deflections of the bridge models. The L VDTs were connected to a Vishay scanner and their outputs were recorded using Strain Smart software. All bridge models were tested by hanging known loads from the bridge and then measuring the corresponding deflections. The bridge models were first tested without any simulated corrosion or cracks. The theoretical deflections of the perfect models were calculated using standard beam deflection equations. Experimental deflection results were compared to theoretical values for consistency and to detect any unforeseen problems with the testing setup. Cracks were then introduced into the bridge models by milling away a measured portion of the steel models. Next, corrosion was induced by exposing the bridge models to a mixture of nitric acid and calcium chloride. The defective bridge models were loaded in the same manner as the perfect bridge models to determine the additional deflection caused due to cracking or corrosion. Current bridge inspection is based solely on visual examination. The results of this study suggest that in-situ deflection data should be used in combination with visual inspection to better locate areas of a bridge with potentially tragic structural deficiencies.

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Apr 21st, 8:00 AM Apr 21st, 10:00 AM

The Effect of Corrosion and Cracks on the Safety of Steel Bridges

CSU 284

The motivation behind this research was the recent collapse of the I-35W Bridge in Minneapolis, MN. The purpose of this project was to build models of single-span bridges to examine the change in their deflections due to corrosion and cracks. Four linear variable differential transmitters (LVDTs) were carefully calibrated and used to measure the deflections of the bridge models. The L VDTs were connected to a Vishay scanner and their outputs were recorded using Strain Smart software. All bridge models were tested by hanging known loads from the bridge and then measuring the corresponding deflections. The bridge models were first tested without any simulated corrosion or cracks. The theoretical deflections of the perfect models were calculated using standard beam deflection equations. Experimental deflection results were compared to theoretical values for consistency and to detect any unforeseen problems with the testing setup. Cracks were then introduced into the bridge models by milling away a measured portion of the steel models. Next, corrosion was induced by exposing the bridge models to a mixture of nitric acid and calcium chloride. The defective bridge models were loaded in the same manner as the perfect bridge models to determine the additional deflection caused due to cracking or corrosion. Current bridge inspection is based solely on visual examination. The results of this study suggest that in-situ deflection data should be used in combination with visual inspection to better locate areas of a bridge with potentially tragic structural deficiencies.

Recommended Citation

Marr, Christopher M.. "The Effect of Corrosion and Cracks on the Safety of Steel Bridges." Undergraduate Research Symposium, Mankato, MN, April 21, 2008.
https://cornerstone.lib.mnsu.edu/urs/2008/oral-session-02/4