Hai Nguyen, PhD, Research Associate, Rahall Transportation Institute, Marshall University
Weathering steel (WS) is a high-strength, low-alloy steel that has been proven to provide a significantly higher corrosion resistance than non-weathering carbon steel. It is best known under the trademark COR-TEN or Corten steel. Although the initial material cost of WS is more expensive than that of traditional steels, it eliminates the need for painting, leading to reduced maintenance cost. In addition to its cost-effectiveness, WS provides some environmental benefits since no painting is required, no volatile organic compounds are released during maintenance painting, nor does disposal and containment of paint pose a concern. There are a large number of WS overhead sign structures in the West Virginia Department of Transportation, Division of Highways (WVDOH)’s inventory, but official inspection guidelines from WVDOH have not been developed yet. This research focuses on developing comprehensive inspection forms and rating methodology to document all structural deficiencies of sign structures in the state.
The inspectionprocess is very important to prevent sudden structural failure of signs and to ensure safe highway operations. Routine inspections of sign structures are typically completed using only the visual inspection technique and as such rely heavily on subjective assessments made by inspectors. Although the visual inspection has the advantage of being simple and powerful, only surface cracks can be found by this technique. In addition, the size of cracks that can be found is limited by the capability of human eyes. In light of this, the visual inspection should be combined with a non-destructive evaluation technique, which can effectively detect defects in structural components without damaging the material. The ultrasonic testing (UT) technique was used in this study to (1) measure section losses of vertical columns near the column bases; (2) detect fractures of anchor bolts and connection bolts; and (3) quantify thicknesses of base plates and splice plates.
Twenty-six comprehensive inspection forms were developed to objectively evaluate the current condition of the 11 general types of sign structures. The work included performing extensive field inspection of the elements of each sign structure including the foundations, drainage issues, base plates, grout pads under base plates, anchor bolts/nuts/washers, connections between base plates and vertical columns, vertical columns and horizontal chords, connections between vertical columns and horizontal chords, welded splice connections, and attachments. A rating methodology was developed to evaluate the sign structures at both the element-level and their overall condition. The element condition was rated based on the developed rating criteria and score. The overall condition of each sign structure was then evaluated by the ratio between the total score of each structure (S) and its maximum possible total score (Smax).
The interstate system within the Charleston, WV area includes 82 WS overhead sign structures (Photo 1), which were evaluated using the inspection forms and rating methodology. Based on this analysis, 10 percent were found to be in poor condition, 64 percent were in fair condition, and 26 percent were in good condition. The rating system is intended to assist the WVDOH to make rational decisions on whether there is a need to repair or replace at-risk elements or connections. Future works will focus on development of a management system such that if a field inspection reveals any serious element or defect that is common to a particular structure type or failure of a particular sign component(s) poses imminent danger to the structure or the traveling public, the WVDOH Project Manager would be notified immediately. Inspection guidelines will also be developed based on the outcome of this study. Final report of this project is publicly available in the below link:
http://www.mticutc.org/assets/pdf/Final_Report-_Weathering_Steel_Overhead_Sign_Structures.pdf
For more information about this project, contact Dr. WaelZatar at zatar@marshall.edu
Photographs:
 |
| Photo 1 Weathering steel overhead sign structures in WVDOH’s inventory |
 |
| Photo 2 Moderate-to-severe corrosion of connections between vertical column and horizontal chord |
Authors’ information:
Dr. WaelZatar is a Structural Engineering Professor and Dean of the College of Information Technology and Engineering at Marshall University. He also serves as Director of the Multimodal Transportation &Infrastructure Consortium (MTIC) and Associate Director of the Mid-Atlantic Transportation Sustainability UTC.
Dr. Hai Nguyen is a research associate at the Nick J. Rahall, II Appalachian Transportation Institute, Marshall University. He is a member of Precast/Prestressed Concrete Institute (PCI) and International Institute for FRP in Construction (IIFC).