Photo taken by Mark Dellbringge in September 2010
BH Photo #175800
The historical term for a pony truss was a "low truss" and the historical term for a through truss was a "high truss" and as far as I know, half-through was a term usually used the way Art refers to where a bridge combines the features of a deck and through truss.
At least this bridge is properly categorized in bridgehunter as a "MODERN" bowstring, which is extremely important because bridge historians like myself use this website and for historians, a "bowstring truss" refers to one of the most significant types a bridge: a design of bridge that was initiated by Squire Whipple, and adapted and often re-patented by other companies. They were built from the 1850s mostly through the 1870s and are usually of cast and wrought iron. These masterpieces of engineering and craftsmanship deserve to stand on their own, separate of these modern mass-produced welded pre-fabs.
Thanks Art! Good explanation, although in my experience I've always seen "pony" used synonymously with "half through". I believe over the years the distinction between the two may have been lost, at least with the engineers I deal with. I am certain that the bridge pictured is a true "bow" design. Regards. Gil.
Sorry for the bluntness in my previous post.
In most definitions a pony truss is a bridge with no overhead bracing whereas a half-through truss is a bridge where the deck is part way between the lower and upper chord. So, although this bridge is a pony truss and a half through truss the two terms are not synonymous. A half through truss can have overhead bracing.
Regarding the bowstring. Technically you are correct you can call the layout a bowstring. However, while I haven't done the calculations, I strongly suspect that the curved chord structure is more decorative than structural on these new bridges.
Much as cheap computing power has eliminated most elegant code, cheap (relatively, as compared to the 19th century)reliable material has resulted in may brute force, inelegant designs (of course there are magnificent exceptions!).
Also, while I haven't researched it, during the 19th century, pony tended to mean small or diminutive. The term was applied to train engines as well as some types of non-driving wheel trucks on engines. So I suspect pony truss refers to a truss that is so small in stature as to not allow overhead bracing.
I may not, I'm just a bridge engineer, not a historian. I'll readily admit there is plenty I don't know. But that is certainly a bow truss, and present day engineers that I know refer to the cross section as a "pony" truss.
I don't think you know what you are talking about.
Correction to my last email - the pony truss is also known as a "HALF through" truss. Do any of you know where the term pony comes from? Thanks.
To the detractors... The bridge is in fact a bowstring truss, and it also is a pony or "through" truss, which merely refers to the cross section view having no overhead bracing. It may not fit your vision of what a "historic" bowstring should is, but that's what it is. I too agree it would be nice to relocate and save the old historic bridges.
THE OTHER ANONYMOUS BEAT ME TO IT BUT WHO CARES...
Squire Whipple turns over in his grave at the thought of this MOB being called a bowstring truss.
Gotta be honest here.......I don't like Steadfast MOB's!!
WAY too many historic bridges out there that need a good home to justify buying one of these "wannabe's".
Based on the provided photos, would this be more accurately described as a pony truss rather then a through truss?
A historic bridge on a pedestrian trail is replaced by a modern MOB...
MOB - another great pontist acronym!
As for the Turkey River Bridge, I witnessed a tractor (not mine) that had to weigh far more than five tons cross it. I thought for sure I was about to witness a bridge collapse, but that old bowstring held.
This is a MOB. (Mail Order Bridge). Steadfast is part of the same company as Continental Bridge, and both prefabricate welded spans mostly for non-motorized use. Every time I see one I see a lost opportunity to relocate and preserve an otherwise doomed historic truss bridge.
It is interesting to note that the weight limit of this new MOB bridge is only 5 tons. Had a historic iron bowstring bridge, such as the Little Church Road Bridge in Iowa, http://www.bridgehunter.com/ia/winneshiek/turkey-river/ been relocated to this site instead, they could have had a stronger bridge for probably not much more money, plus they would have a nationally significant historic bridge.