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Acoustic Emission Monitoring of Fatigue Cracks in Steel Bridge Girders

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Date Created
1999-09
Report Number
1999-36
Description
This report presents results from a laboratory study and field implementation of acoustic emission monitoring of fatigue cracks in cover-plated steel bridge girders. The acoustic monitoring successfully detected growing fatigue cracks in the lab when using both source location and a state of stress criteria. Application of this methodology on three field bridges also proved successful by detecting a propagating crack in two of the bridges and an extinguished crack in a third bridge. Researchers tested a double angle retrofit, designed by the Minnesota Department of Transportation, both in the lab and in the field of girder with fatigue cracks in the top flange. This retrofit does not require removal of concrete deck, and only involves bolting the retrofit to the bridge girder web. The double angle retrofit applied to laboratory test girder resulted in a reduction of flange stresses by 42 percent. Field implementation of the retrofit had mixed success. On one bridge, stress ranges in the cracked flange was reduced by 43 percent. However, on a second test bridge, the reduction was only 8 percent, likely due to the inadequate space for proper installation of the retrofit.

Material Properties and Corrosion Condition of a Twenty-Year-Old Prestressed Bridge Girder

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Date Created
1992-05
Report Number
93-03
Description
This report presents results of a series of nondestructive tests to estimate the strength of concrete in a twenty-year-old prestressed bridge girder removed from an interstate overpass. Nondestructive test results were compared with compressive strength tests of cores. In addition, chloride ion concentration of the concrete was analyzed to determine whether corrosion of the bridge reinforcing steel may have occurred. Nondestructive tests included rebound hammer, pulse velocity, Windsor probe, and break-off tests. Included is a review of commonly encountered strength correlations for each of the tests. Of the nondestructive tests, the rebound hammer and pulse velocity tests predicted concrete strength reasonably well with existing correlations. With one major exception, results from chloride ion tests indicated that sections of the bridge with greater exposure to deicing salts had a greater amount of chloride penetration. The exception was a facia girder exposed to incoming traffic. Rain may have had a beneficial effect by washing salt residue from the facia girder. Chloride ion penetration at the leveI of the reinforcing steel for the bridge girders tested was not found to be great enough to expect corrosion.

Reusability and Impact Damage Repair of Twenty-Year-Old AASHTO Type Ill Girders

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Date Created
1992-05
Report Number
93-04
Description
Prestressed concrete has been used as a bridge construction method in the United States since 1949. Presently, there are thousands of pretensioned prestressed concrete bridges in service in North America. Each year, approximately 200 girders are damaged as a result of impact damage (primarily overheight vehicles striking a bridge from below). This report describes the results of a four girder test series used to evaluate impact damage and effectiveness of repairs. The girders used for the study were fabricated in 1967 and placed into service. The girders were removed from service in 1984 as a result of a road realignment project. The objectives of the research project were to: 1) determine the effective prestress in the strands after 20 years; 2) determine the influence of impact damage on girder performance; 3) evaluate the performance of two impact damage repair schemes under static, fatigue and ultimate loadings; and 4) develop a model to estimate the strand stress ranges in damaged girders.

Field Instrumentation of Steel Highway Bridges

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Date Created
1993-02
Report Number
94-15
Description
Two projects dealing with field instrumentation of bridges are described in this report. In the first project, a portable, rugged and multi-purpose bridge instrumentation system was developed. This was accomplished by using fourteen removable instruments and a portable data acquisition. The instrumentation included eight reusable strain sensors and six inclinometers, which allowed load distributions, stresses, and displacements to be measured in steel girder bridges. In the second part of the project the portable data acquisition system was used to measure strains near fatigue critical details in steel bridges to determine stress ranges under both controlled and random traffic. For this part of the project conventional strain gauges were also used. Overall this acquisition and modelling system worked quite well for determining strains and deflections of simply supported bridges under static loadings. A new measurement technique for finding deflections, based on slope sensors, was developed and verified. This technique can now be readily used in bridge evaluation. The system should be extended now to various types of bridges including continuous span, concrete girder, and timber bridges.

Retrofit of Wood Bridges

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Date Created
1993-02
Report Number
94-16
Description
A retrofit scheme to widen and strengthen nail-laminated timber bridges was evaluated in this project. The scheme consists basically of laying a second, transverse layer of timbers above the existing deck, and casting a grout layer between the two wood ones to insure good force transfer. An old wood bridge was evaluated before and after it was retrofitted in order to investigate the effectiveness of the retrofit technique. In addition, three laboratory specimens, representing portions of the retrofitted bridge deck (ungrouted and grouted), were tested to investigate the strength and the effects of fatigue on the retrofitted bridge deck, and to evaluate the transverse load distribution of the original and retrofitted bridge deck. An analytical model of the retrofitted bridge deck was also developed utilizing the finite element method, the deflection and transverse distribution results from the model studies were compared favorably with the laboratory results.

Putting Research into Practice: Creating a New Bridge Information Management Tool

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Date Created
2008-11
Report Number
2008RIC08TS
Description
This Technical Summary pertains to LRRB’s Research Implementation Committee’s product 2008RIC08, “Development of Scalable Technology to Enhance Transfer of Bridge Information,” released in October 2008. Note: because the final deliverable for this project was not a research paper, it is not stored in the MnDOT Digital Library.

Using Silica Fume Concrete With Full-Depth Bridge Deck Construction in Minnesota

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Creator
Date Created
2001
Report Number
2001-18
Description
This report presents the results of a research project to evaluate the performance of six full-depth silica fume bridge decks, constructed between 1997 and 1999. The Minnesota Department of Transportation (Mn/DOT) constructed these decks to compare their performance and constructability in Minnesota, which involves the use of a seven-inch structural slab followed by a two-inch low slump overlay. Researchers conducted air content and slump field testing, visual inspections, and laboratory testing on chloride permeability, compressive strength, and hardened air system properties. In addition, they compared initial costs between the current deck system and the full-depth silica fume decks. The overall performance of the silica fume bridge decks has been good; however, two of the bridge decks did have problems related to the development of silica fume balls. Laboratory testing has shown that silica fume concrete performs better in terms of chloride permeability and compressive strength. Field tests have shown that placement of the silica fume concrete is comparable to a conventional concrete mix. Finally, cost comparisons have shown the placement of a full-depth silica fume deck to be slightly lower than the current deck system.

I-35W & Mississippi River Bridge Anti-Icing Project

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Creator
Date Created
2001
Report Number
2001-22
Description
A bridge that spans the Mississippi River on U.S. Interstate 35W in Minneapolis, Minnesota has been fitted with a computerized system that sprays potassium acetate, the anti-icing chemical selected, on the bridge deck when data from sensors and a Road Weather Information System determine that hazardous winter driving conditions are imminent. The I-35W bridge (9340) was a candidate for this high-tech treatment due to the high incidence of winter traffic crashes on the bridge. The bridge is more susceptible to "black ice" and slippery conditions because of moisture from the Mississippi River's St. Anthony Falls, nearby power plants and industrial facilities, and of the high volume of traffic on the bridge. (Year 2000 average daily traffic is approximately 139,000 vehicles.) The formation of "black ice" is due to the combination of extreme cold and heavy vehicle exhaust from congestion on the bridge. In addition to traffic safety, the anti-icing system also contributes to sustainability, because the chemical used is environmentally less toxic and corrosive than sodium chloride, which traditionally has been used. This paper describes the anti-icing system and its operational test results.

Analysis Tools and Rapid Screening Data for Distortional Fatigue in Steel Bridge Girders

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Date Created
2001
Report Number
2002-06
Description
Fatigue cracking often occurs in composite bridges with unstiffened girder web gaps at the ends of transverse stiffeners. In this project, researchers sought to better understand bridge diaphragm deflection behavior and advance the ability to estimate web gap distortional stress. Trends from the parametric studies led to general observations that may assist in identifying fatigue-prone bridges. Variables that influence diaphragm deflection behavior include girder spacing, bridge skew, span length, and deck thickness. Transverse load distribution properties appear to play the most significant role in determining the magnitude of differential deflection. Parameter study stress trends indicate that out-of-place distortional stress in fatigue prone web gaps primarily depends on web gap properties, bridge span length, and angle of skew. Differential deflection and web gap dimension trends apply to a varied spectrum of bridge configurations. The research resulted in a method to assess bridge girder differential deflection and distortional stress in actual steel bridges without complex analysis and modeling. Proposed procedures for evaluating out-of-plane stress should prove practical and aid in screening, identifying, and assessing bridges vulnerable to distortion-induced fatigue cracking.