Weathering Steel Bridges Were Generally A Cost Effective

Weathering Steel Bridges Were Generally A Cost Effective

Weathering steel bridges were generally a cost effective In 1984, Albrecht and Naeemi also conducted an extensive evaluation of weathering steel performance. This study reviewed the bridges inspected and states considered in the AISI (1982) study as well as the experiences of other states that...
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Weathering steel bridges were generally a cost effective

In 1984, Albrecht and Naeemi also conducted an extensive evaluation of weathering steel performance. This study reviewed the bridges inspected and states considered in the AISI (1982) study as well as the experiences of other states that had reported less than optimal performance of weathering steel bridges. Specifically, bridges in both Alaska and California that exhibited excessive corrosion were evaluated; it was concluded that site conditions with heavy rainfall, fog and high humidity were subjecting these structures to prolonged periods of wetness leading to the poor performance of weathering steel. Albrecht and Naeemi (1984) also reported that two of Louisiana’s sixteen weathering steel bridges were not performing as expected. Both of these were located in close proximity to the Gulf of Mexico and it is believed that salt contamination (as a result of salt-laden wind and fog) and high humidity were both factors preventing formation of a protective oxide coating. They also reported several cases of inadequate weathering steel performance in Ohio. The cause of corrosion in these structures was also attributed to prolonged periods of wetness caused by low clearance over underlying streams. Chemical analysis of rust samples taken from one of these bridges showed only trace amounts of sulfates 361-3 and chlorides, indicating that neither salt contamination nor pollution was a likely cause of the excessive corrosion observed. Conclusions of the Albrecht and Naeemi study (1984) were in general agreement with the finding of the AISI First Phase Report (AISI 1982); Albrecht and Naeemi also state that the majority of weathering steel bridges are in good condition, but local areas of pronounced corrosion exist in several structures. Subsequent to the initial investigation on weathering steel bridges by AISI a second study was conducted and the results are summarized in “Performance of Weathering Steel in Highway Bridges: A Third Phase Report” (AISI 1995). In this study, researchers from AISI revisited the bridges that were initially inspected in the Phase I Report (AISI 1982, referenced above) and also inspected several additional bridges. These were located in West Virginia, Louisiana, Iowa, California, and Puerto Rico.

Findings of this evaluation indicated that weathering steel bridges that are designed and detailed in accordance with the FHWA Technical Advisory on weathering steel bridges (T 5140.22, FHWA 1989) were performing well throughout the United States, including those in marine and industrial environments. However, other researchers have found that the distribution of airborne salts in marine environments may vary greatly from location to location and have noted structures in these environments where the weathering steel has not performed adequately. AISI also reports that several bridges inspected were located in areas of high rainfall, high humidity, or frequent fog and no problems were observed with any of these bridges. The only weathering steel bridges that were found to be performing unsatisfactorily were those located in the metropolitan Detroit area. It was thought that the negative performance of these bridges was due to the amount and frequency of deicing salts used in the Detroit area, the chemical composition of these salts, or a combination of both of these factors. Additionally, local areas of corrosion were reported for some bridges; the most common causes of these problems were reported to be leaky deck joints and clogged scuppers. In addition to the above-mentioned studies, several states have independently evaluated weathering steel bridges in their inventory and these include: Louisiana, Idaho, and Texas. Louisiana has cited corrosion problems in some of its weathering steel bridges, particularly along the gulf coast, due to airborne salts (Raman and Naszrazadani 1989). The primary locations where excessive corrosion was found to develop include areas: (1) near piers, (2) where wildlife (particularly birds) sheltered, (3) where condensed water collected and pooled, and (4) at locations with accumulated debris. In their research, Raman and Naszrazadani cite instances in which the application of a tannic acid solution was found to stabilize the corrosion rate (1989). However, it is not yet known if this would be acceptable as a general practice. In 1995, the Idaho Transportation Department inspected 12 of its 40 unpainted weathering steel bridges (Jobes 1996). A protective oxide coating was observed on all 12 of these bridges and the continued use of weathering steel bridges in appropriate environments was recommended. The Texas Department of Transportation (TxDOT) has also recently completed a study focusing on the performance of weathering steel used in bridges in that state (McDad et al. 2000). During this project, 40 weathering steel bridges throughout the state were independently inspected. The bridges were selected to be representative of five different site conditions: coastal, industrial, urban, suburban, and rural. The inspections revealed similar findings for all of the bridges except for those in coastal areas. In particular, the interior surfaces of bridges in coastal areas had larger flakes than the other bridges inspected; the exterior surfaces of the coastal bridges were similar to those of the other bridges evaluated. McDad et al. (2000) concluded that weathering steel bridges were generally a cost effective alternative for use in Texas. The situations in which they did not recommend its use were: (1) in the presence of corrosive industrial or chemical pollution, (2) in locations of heavy salt-water spray or salt-laden fog, (3) uses in conjunction with timber decking, and (4) in depressed roadway conditions over roadways on which deicing salt is used. While the above studies confirm that weathering steel bridges perform favorably in most locations in the U. S., they have also revealed that there are some sites where weathering steel may not perform as intended. Specific areas 361-4 where weathering steel should be used cautiously include: (1) locations with frequent rainfall, fog, or high humidity, (2) sites with topography that may subject the steel to excessive periods of wetness, (3) low-level water crossings, (4) marine environments, (5) locations where concentrated chemical pollution may drift directly onto the structure, and (6) in depressed roadways. The above studies have also attributed the excessive, local corrosion of some weathering steel bridges to problems with design details. One of the most significant sources of this type of corrosion is due to leaky bridge joints. Similarly, it is of significant importance that consideration is given to controlling drainage on and around a weathering steel bridge.

weathering steel bridges were generally a cost effective