MNA - White River Bridge (Cotter)

The railroad swing truss bridge at Cotter was designed to swing open so that steamboats (with tall smoke stacks) could pass through when going up or down stream.

It is common that many call this type through bridge as a "Pratt" Truss. But it is not. It is a "Howe" Truss.

Reference:

https://skyciv.com/education/types-of-trusses/#howe

This through truss bridge at Cotter is really a "Howe" truss design. A Howe Truss is an upside-down Pratt.

For a "Pratt" type, when supported by piers on each end, the diagonal structural members (within the truss) slope downward in the direction to the center of the span.

For a "Howe" type, when supported on each ends by piers,

structural diagonal members within the truss slope downward in the direction of the ends of the span.

In the "Howe" design, (all but one) vertical structural members are in tension, directly holding up the bridge's deck below.

For the "Pratt" type, when supported on each end by piers, within the truss it has sloped diagonal downward members that point towards the center of the truss; and those "diagonal" members are in tension holding up the bridge's deck below. Just the opposite as in the Howe design where it pulls up "vertically".

If the Cotter "Howe" bridge was swung open, then the center bridge pier holds up the entire through truss bridge. The end piers no longer hold the truss bridge up. During the open period all the prior tension structural members become in compression. During the open period all the prior compression structural members become in tension. In the open position the bridge become a double cantilever structure. Since the Howe truss design has structural diagonal members sloping downward towards the bridge's ends, when swung open, those sloped members are pulling on the bottom of the truss, to effectively hold up the ends from straining downward.

The Howe and Warren truss designs are desired for swing bridges with only a center pior (when opened). For truss bridges that are not to be swung open, the truss can be either a Pratt, a Howe or the Warren design.

Take a look at;

Reference:

https://skyciv.com/education/types-of-trusses/#howe.

...

I think it would be prudent not to say that the bridge

swung open only once! That should be deleted. It is not needed in the description.

There are some people in Mountain Home, AR

that think that is not the case.

A few steamboat records imply they went

north from Buffalo City.

Just a few times, but can not be proven since

the St. Louis Iron Mountain and Southern Railroad

did not have any records. Many steamboats even operated at night.

It's hard for me to believe that the White river was a navigable steam to begin with. That being said,I think the placement of the the swing pier could interrupt the natural flow of the river and cause it to change course. I've been to Cotter and the river there looks more like a float trip stream. Can't imagine any steam boats going by here.

The Cotter Bridge photos below were taken by me but posted to the RR bridge, so I'll post RR bridge pictures here also. Visted the bridges about 5 pm on 2 March 2007. As mentioned below the RR bridge is best photographed from the west bank parking lot and from the overlook on Hwy 62. The RR crossing at the west bank also gives a good perspective of the tracks running under the smaller Cotter Bridge arch. There is a large ring gear on the center pier so this bridge would have pivoted when built. None of the other swing mechanisms remain.

Webmaster's note: The photos that were here have been incorporated into the main site.

This bridge has not moved in my lifetime...in other words since early in 1959. I grew up visiting my grandparents who lived about 3/4s of the way up the hill on Hwy 62 in Cotter on the river side. We could see this bridge, and the entrance to the tunnel from my grandpa's deck and back yard. A man named Frank Young (my grandpa's best fishin buddy), who grew up in Cotter, (the old water tower was in his back yard at the top of the hill)said the bridge was unique because it went directly into the tunnel.

Riley, this is a bridge you should see if you are in the area. The center cement pier is round and the bridge sits on a large cog wheel gear. I believe I was told there use to be a little operator cab on the side of the bridge at the center. It was motorized, (I don't know how, electric or gasoline engine?) and the bridge turned sideways to allow steamboats to pass up and down the White River. The center span is now mostly over dry ground, as the course of the river has shifted.

There is a nice book about the White River Railway written by Walter Adams, if you could get a copy if it. It is no longer in print, but one might showup on Ebay.

If you would care to email me direct I will send you a photo I took last Sunday of the large center pivot gear.

I hope this is helpful.

Dave near Branson, Mo.

I would like to know where I could find more information about this particular bridge.