verifying 1920 bridge steel type by hardness testing
 

verifying 1920 bridge steel type by hardness testing
we are trying to confirm the actual steel type and allowable stress for a 1921 historic truss bridge which some in our city are targeting to demolish and replace with a new concrete bridge. one caltran calculation error has already been discovered which increased the bridge sufficient rating from 2 to 53.9. if the steel can be confirmed to be a7 carbon steel, the rating would be increased to 65 which is significant since the 20 foot width of the bridge lowers the rating by 19 points soley due to the width.
tensile testing of coupons cut from the floor members has been suggested as a verification means. however, statistical modification of such data would require an unreasonable number of samples.
it has also been suggested that the less invasive method of hardness measurement could also confirm the steel type. sufficient data could be taken to raise the statistical confidence.
does anyone have any references or professional contacts who can advise on the feasibility, practicality and cost of such hardness testing? the bridge presently has a lead-based coating which is reasonably intact.
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you might have more luck in the structural or bridge engineering forums.