Number of chairs on bridges with longitudinal timbers

[Off Tackle]

I'm currently having a crack at building a plate girder bridge with the rails being carried on longitudinal timbers. I'm using bullhead track with C&L 4 bolt chairs and I'm aiming represent a Victorian era bridge for a branch/mineral line. In the course of my (image based) research there seems to be a variety of spacings when it comes to how many chairs on used on such bridges. Some appear to use a similar spacing to normal sleepered track, but many images show somewhere between 40% - 100% more chairs attaching the rail to the longitudinal timber than is found on normal track. Are there any prototype rules or engineering guidelines that anyone is aware of? 

[Kris]

Can't say for the past but this is an image of current practice taken a few years ago on an organised walk across the Royal Albert Bridge. 

 

[Miss Prism]

On this old-timer, seems to be approximately the same distance as on normal track.

 

[Stephen Freeman]

Possibly, no probably not normal bullhead (maybe bridge rail), if it was then the chairs would be L1s (more commonly called Bridge chairs as they sit better on longitudinal timbers, normal chairs would be too wide).

[DLT]

Some good detail photos of Barmouth Bridge HERE  But the site is a blog, so very difficult to search.

A Google search for Railway Bridge Deck brings up some photos and diagrams.

Cheers, Dave.

[Trog]

21 hours ago, Stephen Freeman said:

Possibly, no probably not normal bullhead (maybe bridge rail), if it was then the chairs would be L1s (more commonly called Bridge chairs as they sit better on longitudinal timbers, normal chairs would be too wide).

 

L1 chairs are for use with ordinary 95lb RBS bullhead rail, they are often used at the heel end of switches as the rails are still often too close together to allow the use of two S1 / AS1 chairs. The even smaller M1 chairs are most often seen used in the middle area of slips where the rails are really packed together. While L1 and M1 chairs can be used on long timbers it is better to avoid particularly the M1 type as their smaller foot print increases the load per unit area on the surface of the long timber. There is however a special chair similar to an M1 designed for smaller cross section long timbers, where the chair screws are angled inwards to reduce the chance of them bursting the side out of the timber.

[Jeremy Cumberland]

On 27/11/2022 at 15:52, Stephen Freeman said:

Possibly, no probably not normal bullhead (maybe bridge rail), if it was then the chairs would be L1s (more commonly called Bridge chairs as they sit better on longitudinal timbers, normal chairs would be too wide).

 

I have only ever encountered normal rail (bullhead or flat bottom) being used on bridges. I always understood "bridge rail" to be called this because the section looks like a bridge, not because it was used om bridges. Bridge rail might have made sense in the days of wrought iron (Brunel clearly thought so), but It makes little sense that I can see to have a hollow head and incliined edges when rails are rolled from steel.

 

Bullhead rail uses bridge chairs with square bases, as you say.

[Off Tackle]

Thanks for all the replies everyone, much appreciated. Going with a 'standard' chair spacing with my bullhead rail, the deal was sealed by that wonderful image from @Miss Prism! Nearly every image I have (about 30 off the web, hesitate to post any here due to copyright issues) with additional chairs are with flatbottom rail and pandrol style clips/baseplates. I did look for bridge chairs before buying the C&L 4 bolt ones, and I think the ones I needed - the Exactoscale 4CH 201A  4-bolt L1 bridge chair - were only available via one of the societies. As my bridge is pretty short requiring less than 100 chairs I couldn't justify spending more joining a society than the actual chairs, but now I'm some way into building the bridge superstructure and am building the timbers I'm having second thoughts...ha'p'orth of tar and all that. The timbers I've built are 6.5mm wide to accommodate the chairs and that combined with the OO gauge does somewhat make the central trough look a bit too narrow. 

 

I'll post some pics as I progress. 

[Trog]

On 25/11/2022 at 18:59, Kris said:

Can't say for the past but this is an image of current practice taken a few years ago on an organised walk across the Royal Albert Bridge. 

 

 

I thought that current practice was to have a third rail sited on the sleeper ends usually on the 6' side and 3" above the plane of the running rails?

[Stephen Freeman]

15 hours ago, Jeremy C said:

 

I have only ever encountered normal rail (bullhead or flat bottom) being used on bridges. I always understood "bridge rail" to be called this because the section looks like a bridge, not because it was used om bridges. Bridge rail might have made sense in the days of wrought iron (Brunel clearly thought so), but It makes little sense that I can see to have a hollow head and incliined edges when rails are rolled from steel.

 

Bullhead rail uses bridge chairs with square bases, as you say.

I only mentioned bridge rail as the photo seems to show that in use, nothing to do with use on bridges, sorry if that confused.

[St Enodoc]

Have a look at the second photo on this post: