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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.

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.

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.

A report summarizing the results of field surveys done on the Tenth Avenue Bridge in Minneapolis, Minnesota, with recommendations for repairs.

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.

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.

This Technical Summary pertains to Report 2023-13, “Assessment of Bridge Decks with Glass Fiber-Reinforced Polymer (GFRP) Reinforcement,” published March 2023

By February 1 of each odd-numbered year, the commissioner shall submit a report electronically to the members of the Senate and House of Representatives committees with jurisdiction over transportation policy and finance concerning quality assurance for bridge inspections. At a minimum, the report must: (1) summarize the bridge inspection quality assurance and quality control procedures used in Minnesota; (2) identify any substantive changes to quality assurance and quality control procedures made in the previous two years; (3) summarize and provide a briefing on findings from bridge inspection quality reviews performed in the previous two years; (4) identify actions taken and planned in response to findings from bridge inspection quality reviews performed in the previous two years; (5) summarize the results of any bridge inspection compliance review by the Federal Highway Administration; and (6) identify actions in response to the Federal Highway Administration compliance review taken by the department in order to reach full compliance.

This cover letter accompanied the 2009-2010 Biennial Report on Bridge Inspection Quality Assurance.

By February 1 of each odd-numbered year, the commissioner shall submit a report electronically to the members of the Senate and House of Representatives committees with jurisdiction over transportation policy and finance concerning quality assurance for bridge inspections. At a minimum, the report must: (1) summarize the bridge inspection quality assurance and quality control procedures used in Minnesota; (2) identify any substantive changes to quality assurance and quality control procedures made in the previous two years; (3) summarize and provide a briefing on findings from bridge inspection quality reviews performed in the previous two years; (4) identify actions taken and planned in response to findings from bridge inspection quality reviews performed in the previous two years; (5) summarize the results of any bridge inspection compliance review by the Federal Highway Administration; and (6) identify actions in response to the Federal Highway Administration compliance review taken by the department in order to reach full compliance.