Number of Transoms per Panel

[Kevin Hunter]

Apologies in advance if this is a daft question...... but have been thinking about dragging my bridge out of storage to build it, and I'm curious about some details.

Photographs of real Bailey Bridges appear to show 2 transoms per panel, one crosses at the end of a panel and one at the mid point. At either end of a bridge there is an extra transom fitted outside of the final panel and held under the clamp on the end post. This is usually the top of the on/off ramp.
Hopefully the photo will illustrate the point I'm trying to make (thanks, Charles, for supplying the original picture in a recent post).

The model appears to have 4 transoms per panel, one at each end and two in the centre. As panels are joined, the transoms at either end of each panel "double up". The same is true at the ends of the bridge, where the transom held under the end post clamp supports the ramp and doubles up with the panel transom.

So.... were bailey bridges always built with single transoms or did it vary depending on intended load? Most pictures suggest fewer transoms were used than in the model, besides which I suspect the load bearing capabilities were determined by the side panels (single, double, double double, etc). Is the Armortek bridge built with (apparently) extra transoms in order to guarantee weight bearing integrity in small scale? Or, is there some other explanation which I'm missing?

Interested to hear any thoughts.

Kevin

[Adrian Harris]

As far as I can recall, it was two transoms per bay up to a 40 ton load (Class 40 bridge ?) and four transoms per bay over 40 ton loads.

Adrian.

[Kevin Hunter]

So, a slightly daft question after all
Despite many pictures only showing 2 per bay I clearly should have researched further to spot the more "beefed up" versions. Act in haste...... as they say.

As always Adrian, many thanks for your assistance.
Regards
Kevin

[Charles A Stewart]

Afternoon all, found this on web which may be of use, apologies if I am talking to the converted.

https://archive.org/details/in.ernet.dl ... 2/mode/2up

Certainly explains the metal ribands though, still working on the wooden ones, lunch ready must go.
Take care

Charles

[Pete Mallett]

Your Question isn't daft at all and you do seem to have partly answered it for yourself. The more Transoms they greater weight it could take. The problem with the Armortek BB is that it can actually take more transoms than the original. On the middle vertical brace it was only ever possible to place one transom because there was only hole, in the vertical member, for one transom clamp (see transom marked 2 in your own photo). The Transom Clamp went through the vertical member and a swing arm then came down and hooked under the transom seat on the bottom chord. Because there is only one hole in the vertical it can only take one transom clamp so it is impossible to have two transoms here, one either side of the middle vertical.

Incidentally, the end transoms, where the ramp joins, were always packed, from underneath, at several points. This was because when the tanks drive up the ramp they rock for a moment of that transom before transferring all their weigh on to Bridge deck. For that single moment the entire weight of the tank is bearing on on a single transom and and in order to stop that transom from buckling under the sustained weigh the transom was packed!

The Steel Curb was designed by the Yanks and was very similar to the curb they used on the Steel Treadway. They called it a Guard rail. it was brought in following four accidents, on the Treadway, when Sherman tanks rode up on the existing curbs and caused an eccentric load on the Treadways causing the rubber Pontoons to pop out and the tank to slide into the water. All the accidents happened in one month, September 1943, during training the the US. Seven men lost their lives in these accidents. It was felt that the curved steel curbs helped prevent tracked vehicles from riding up on Curbs. The British didn't agree and said so, 'Driver error will cause any tank to drive over the edge of a bridge, no matter what protection is put there to prevent it'. The Steel Curbs were not used anywhere in the ETO during WWII, as they were not wholly compatible with British Bridges and no, usable, US-manufactured Bridges arrived in the ETO before the end of hostilities.

[Kevin Hunter]

Thanks for your input on this Pete, it's very interesting. However:

On the middle vertical brace it was only ever possible to place one transom because there was only hole, in the vertical member, for one transom clamp (see transom marked 2 in your own photo).

That makes the photo posted by Adrian curious as there are clearly 2 transoms, one either side of the middle vertical brace "a la" Armortek version. Before you say anything, I appreciate that only one of the two centre transoms seems to be clamped and there is no clear evidence in the photo of the 2 transoms being tied together in any way. Could the road deck be relied on to hold "extra" transoms in place?

Kevin

[Adrian Harris]

If you zoom in on the original picture on WikiPedia, you can see the middle two transoms are clamped one into each panel, as it's a double panel bridge.

Whitefish_Falls_Ontario.jpg (101.56 KiB) Viewed 4793 times

I doubt you would build ever a single panel bridge with double transoms, so only having one hole wouldn't be a problem.

Adrian.

[Armortek]

[Kevin Hunter]

Thanks Adrian and Kian, suddenly becomes obvious.
Downside…..will need to think about even more clamps from Dave

Thanks again
Kevin