INDEPENDENT STUDY OF SIX HOT DIPPED GALVANIZED BRIDGES
FLCA full life cycle assessments indicate cost reductions of 15.46 to 26.45 dollars per sq. foot to the first maintenance stage of the bridge. Additional cost reductions would be expected beyond first reconditioning.
An independent engineering consultant Mr. John Malone of Galvanizing Consultants, and Mr. Donald Wetzel of the AGA conducted this study. This information plus the application of "Full Life Cycle Assessments" analysis confirms the cost-effective benefits of hot dipped galvanizing for township, city, county and state DOT highway bridge structures. The study was conducted in the fall of 1991 on six hot dipped galvanized bridges located in the state of Ohio. At the time of the study these bridges ranged in age from 19 to 24 years. Today these bridges average 30 years of age, and application ranging from industrial to rural, and lengths ranging from 60 to 227 feet in length.
In the United States, today it is estimated that approximately 600,000 bridges exist. At the time of this article it was estimated that approximately 500 full-galvanized bridges were in existence.
The engineers tested the thickness of the zinc coating on all six bridges. The average thickness that remained after approximately 20 years of service was 6.26 mils. The rate of zinc erosion is very stable and known and can be measured. This exceeds the standard for newly galvanized steel by 2.36 mils or exceeds new standards by 60%. The current ASTM 123-89 galvanizing standard for new steel is 3.9 mils It was also noted in the study that the life expectancies were EXTREMELY CONSERVATIVE and projected a remaining conservative life of 40-90 years at which time 5 % of the bridge structure would be rusted.
STUDY CONDUCTED IN 1991 and THE ESTIMATED LIFE OF THE BRIDGES ARE BELOW
| Bridge | Built | Location | Item | Avg. Remaining Zinc in mils | Years to 5% rust | Comments |
| A | 1969 | Industrial | Structural | 6.34 mils | 53 years | Limestone environment |
| B | 1970 | Rural | Structural | 5.17 mils | 73 years | Evidence of Heavy salting |
| C | 1973 | Industrial | Structural | 5.39 mils | 40 years | Refinery environment |
| D | 1972 | Rural | Structural | 6.68 mils | 90 years | Looked new |
| E | 1968 | Over creek | Structural | 5.51 mils | 75 years | Superb condition |
| F | 1967 | Oldest studied | Structural | 5.88 mils | 49 years | Excellent |
Note: ASTM 123-89 galvanized coat thickness industry standard is 3.9 mils on newly dipped galvanized steel |
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BOTTOMLINE: application of FULL LIFE CYCLE ASSESSMENT (FLCA) principles determine the full cost during the life cycle of the item being measure. Information provided presently indicates in the state of Ohio, the normal practice is to paint highway bridges every 10-15 years. The repainting costs in 1999 dollars are running at 3.00 to 4.00 dollars per foot with a 10-15 year paint cycle life.
COST REDUCTIONS: With 1999 hot dipped Galvanizing costs of approximately 4.00-5.00 dollars per sq. ft. at installation, the below FLCA cost reductions would be expected to the first significant maintenance.
| Bridge | Built | Avg. Remaining Zinc in mils | Years to 5% rust | Year date maintenance |
Total
bridge life w/o maintenance |
Projected FLCA cost reductions over life of bridge @ 15 year cycle |
| A | 1969 | 6.34 mils | 53 years | 2044 | 75 years | 17.64 dollars per sq. |
| B | 1970 | 5.17 mils | 73 years | 2064 | 94 years | 25.06 dollars per sq. |
| C | 1973 | 5.39 mils | 40 years | 2031 | 58 years | 15.46 dollars per sq. |
| D | 1972 | 6.68 mils | 90 years | 2081 | 109 years | 29.16 dollars per sq. |
| E | 1968 | 5.51 mils | 75 years | 2066 | 98 years | 26.13 dollars per sq. |
| F | 1967 | 5.88 mils | 49 years | 2040 | 73 years | 19.46 dollars per sq. |
| Note: in the table above, the Ave. Remaining Zinc thickness in mils after 30 years is still 60% greater than the current ASTM 123 standard for new coating thickness. This is normal occurrance in bridge applications. | ||||||
BOTTOMLINE: If the additional installation cost is less than the expected cost for the alternative then the first choice is better. In this case, if hot dipped galvanizing can be purchased for less than 15.46 dollars per square foot (bridge C) then the choice is definitely galvanize purely based on costs. In this example, accumulated cost reductions over the life cycle of the bridge would range from a minimum of 12.61 to a maximum of 26.31 dollars per sq. ft. Application of present and future dollar principles represents even greater cost reductions. Stark County estimated that on the 247-foot galvanized bridge to install galvanizing was 2.85 dollars per sq. ft.
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