Wow, those pictures are very telling. Rod use is totally different than any that I have looked at. Mr. King kept designing. From the Springfield with no lattice to lattice on the outrigger struts in 1878....love the craftsmen's record.
Looks like the eyebars need a little tightening up. Could be slippage at the feet, we've seen that in the Springfield Bridge.
The Kern Bridge in Blue Earth County, Minnesota, is the longest single-span bowstring in the U.S., at 190 feet. Built in 1873 by WIBC, it's the oldest truss bridge in Minnesota.
Calvin: Thanks for contributing this excellent collection of photos, particularly the detail and under-bridge photos that make much more clear the unique construction of the bridge including post-tensioned floorbeams.
And as long as the discussion here has been about long bowstring spans (I didn't realize Boner bridge was such a large span) its also worth noting that you have to go to Canada to see the longest known remaining bowstring, a Wrought Iron Bridge Company span of 225 feet http://www.historicbridges.org/truss/blackfriars/
WIBC built a number of 200+ bowstrings in America too according to a company list http://www.historicbridges.org/truss/blackfriars/notes1.jpg, but all are gone today.
Simply had to see this beautiful structure for myself. When I visited to update the pictures and see the specifications, I measured the bridge from abutment to abutment. The exact length is 52.2107 meters, or 171.295 feet. Even the King Iron Bridge Company noted it was an unusually long single Bowstring, with the height at the apex at 19.1 feet.
Boner Road Bridge main span is 161 feet bracketed with ponies that are around 47 feet each.
Good information as always. The Boner Road Bridge in Warrick/Spencer County Indiana as well as the Austin Bridge in Chanute, KS have spans reported to be 160 feet.
The 170 foot measurement is from the historic bridge inventory. It was actually the photos which showed a very long bridge that inspired me to look it up. 170 feet would actually make it the second longest bowstring span in the country, pushing the Freeport Bridge in Iowa with its 160 foot span into third place, where previously it was assumed to be 2nd place.
If the 170' length is accurate, then this appears to be the longest single span King Iron Bowstring Bridge listed on this site.