East Buck Creek Bridge
Photo taken by Dave King on September 1, 2013
BH Photo #265450
Fmiser, you raise a very valid point... And, I did say "usually" :) and, there were many Warren ponies in northern Minnesota that have battened double-angle members for both member types...an example is here:
But, look closely...they actually are not identical...one has more battens spaced closer together than the other, and this would be the compression member. It basically serves the same purpose as the v-lacing does, which is prevent buckling of angle members.
An example with battened tension and laced compression members:
This one is much easier to tell the difference between member types--and, I think it looks a lot better.
Matt wrote: "the battened angle members are usually tension members"
Usually. *smiles* But only usually. There are cases of struts - or top chords - built with only battens. But I agree it is unusual.
And, unfortunately for those of us trying to attach labels to these bridges, a short span can be really trying 'cause there isn't space for a pattern to show.
A warren can be built with matching, OR non-matching diagonals. For me, a more decisive factor on this bridge is the vertical only in the center, so if it were a warren, only one panel is "with vertical" - which is unusual. And that there are a number of spans like this that are already labeled "half-hip pratt".
Glad I could help! :) It is a bit tricky with these short spans that can be considered either Pratt or Warren... I remember a couple of years ago, we had a good forum discussion going on this very subject, and it seems that the easy way to tell is that if both diagonals are identical in construction, it's a Pratt; and if they look different from one another, then it's a Warren. If they're different, then that means that they're designed to handle different load types, which is what a Warren is designed to do.
Julie, the battened angle members are usually tension members and are connected every so often, whereas the v-laced members are consistently and closely attached along the whole length. The reason for this is because the v-lacing prevents the actual loaded members from buckling outward from each other, which they would be subjected to being in compression. Tensioned members are being "pulled" rather than "pushed" and are not subjected to buckling, and so batten plates are sufficient.
I guess I went by configuration only, and didn't look at the construction of the diagonals. It would have been more obvious perhaps, if the bridge were more than two panels long.
Now the other question, How(e) did I post twice? I'll delete one.
Hey Matt, want to tutor me in engineering? I need to finally figure this all out. Why battens? Why lattice riveted lacing? Angles in......angles out?
This is actually neither a Howe nor a Warren, but a half-hip Pratt...the diagonal members slope downward as they go toward the middle, taking the Howe configuration out of the picture (the Howe diagonals slope up as they go toward the middle), and the best way to tell these apart from the Warrens is that the opposing diagonals are both identically built up of battens, suggesting that they both are tension members, which is indicative of a Pratt. If it were a Warren, one member would be like these, and the other would most likely be built up with V-lacing to handle compressive forces.
Howe is it not Warren? 8^p
This bridge has a fence on the west end stating no trespassing. Gate was open and could see tire tracks crossing the bridge. Nothing stated the bridge was closed. Looked open to private traffic on a Level B road. All photos were taken from the west side, never crossed the property line.