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ENGINEERS IN
OHIO HAVE BEEN PINONEERING GALVANIZED BRIDGES IN THE U.
S. FOR THE LAST THIRTY YEARS. Galvanizers in the state have been
instrmental in the
fabrication and galvanizing of bridges. Pictured above is a
bridge in Medina County, OHPrior
to galvanizing the county relied on lead-based paints and
expensive sandblasting and repainting programs. Life
expentency of the galvanized ridges under study for 30
plus years indicate extremely conservitive life to first
maintenance of 60- to 90 plus years. First maintenance is
defined as 5% (five) percent rust. County engineers faced with the EPA requirements make it very difficutl and very expensive to repaint truss bridges especially over water. RFP paint contracts for bridges arecoming back as high as 16 to 20 dollars per square foot. Wit hthe cost of hot dipped galvanizing even at todays prices of 3-5 dollars. Galvanizng is cheap. Painting systems have improved over the years, however, even the highest quality painting coating system can not approach galvanizing performance. Testing engineers continue to report galvanizing out performs the best painting systems by 300-500 percent. |
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engineers who are using hot dip galvanizing, where a zinc
coating is applied by immersing the fabricated steel in a
bath consisting primarily of molten zinc, very long
maintenance free life is expected. Maintenance free
bridge life of 50 to 100 years is the norm not the
exception. The vast majority of the galvanizing kettles in the United states are bathtub in size. These small kettles made galvanizing large bridge trusses impossible as a completed unit. There the rules ae are now for ever changed regarding galvanized with our new kettle. The old engineering principles for building bridges are gone with the horse and buggy. The new rules for VERY LARGE fabricated steel structures i.e. bridges follow only one rule.It is the largest kettle in North America.. Galvanizing Galvanizing provides complete coverage of all surfaces, inside box beams, cracks, crevis. As sections of the bridge are fabricated, galvanized covering all welds with a zinc coating. This coating is at least 5 to 7 mils-a level of protection that exceeds the minimum ASTM specification of 3.9 mils.
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Galvanizing forms a mocular bond with the steel mocules providing a rust free coating where as paint coatings fail as soon as a nick occurs. Galvanizing self-healing characteristic is due to the sacrifical cathodic zinc principle which prevents the steel from rusting. 100 percent emersions of the entire fabricated steel structure into the zinc bath assures all nooks, inside surfaces of the bridge will be protected, unlike paint which only covers the visable surface of the bridge. Everything is galvanized on the bridge. If assembling is requred in the field, galvanized bolts are used to join the trusses together. When welding is necessary, for joints or customization in the field, zinc sodder coatings are applied that nearly equal the kettle zinc coatings. |
Summarized from Modern Steel Construction, October, 1997 issue |
In a rural
atmosphere away from the sulfuric and the other corrosive
fumes more common in urban or industrial areas, the
expected service life exceeds 80 years (the expected
service life is defined as the life until 5% of the
surface is showing red iron rust).
Galvanized bridges cost about 10% more than painted or weathering steel bridges, at the time of installation. However, with todays repainting cycles 4 to 5 times more frequent than any hot dipped galvanzing option clearly support galvanzing. In 1999 highway engineers are facing sandblasting and repaiting costs over water of 15 to 20 dollars per square foot, and 4 to 6 dollars per square on state highways. With galvanizng costing at the time of installation in the range of 3-4 dollars makes galvanzing look like a bargain. |
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