Cottonwood Creek Bridge

Thanks Tony, that makes sense. I had just used the term diagonal members or tension rods, so thanks for the more specific terminology.

I have often suspected that wrought iron and steel was both used on some bridges during the 1890s and perhaps even the early 1900s. Have a look at the Long Shoals Bridge in Bourbon Co. Kansas. This is a 1902 Parker through truss with highly decorative portals. I suspect that both wrought iron and steel were used on that bridge.

For anyone reading this, it should also be noted that cast iron was used on bridges before 1876.

You will have to excuse the typo's on the previous post. It's late and I've been up way to long. Good Night!

Robert

Don't worry, it took me years to learn all this stuff. When I went to take Indiana's bridge inspection certification (to work on an iron bridge-mind you, there wasn't one sentence in it about truss bridges. ANYWAY...lets see if I can explain this without being more confusing. In the Pratt truss you have the verticals and diagonals that make up each panel. Designers found that stress reversal(from tension to compression and vice-versa) on a live load could cause fatigue, and possibly even break a diagonal. This is where the counter comes in to "counter"act the effects of the stress reversal. So the diagonal member that crosses the truss diagonal is the counter, together they form an X in the panel. On the earliest bridges it is not uncommon to see every panel countered. As truss bridges became heavier and stronger, counters were usually limited to the center panels where the load was the greatest. In the later years they were sometimes omitted altogether. This turned into a small essay, but I hope helped you.

As for Wrought iron vs. steel. I can't always tell. As a general rule most bridges built prior to 1890 were probably wrought iron. In the early 1890's iron and steel were often mixed. And by the late 1890's stell had pretty well taken over. Wrought iron was such a superior material to steel. I have seen iron bridges unpainted for many years with little or no section loss(rust through) on members, whereas the same bridge in steel would have severe structural problems.

OK I think I've said all I can for now, but feel free to contact me with any other questions. And thanks for all your great pics of Kansas bridges.

Tony

I am going to have to show my ignorance here, but what is a counter?

I also would like to know if this bridge is wrought iron or steel. Are there any easy, simple ways to tell? I know that wrought iron can be bent into different shapes and consequently can be used for more decorative portals.

I've never seen one quite like this. A through truss this short, and all of the panels having counters(including that unusual center panel) would normally indicate a fairly old bridge. It is a pinned span, but can't tell if it's steel or wrought iron.

Upon quick glance, this would appear to be a standard Pratt through truss. The bridge has some rather unique features however. The middle panel is considerably narrower than the others. Notice also that none of the panels have only one vertical member.