Skewd Stone/Brick Arched Bridges - Minimum Angle

[Captain Nick]

I wonder if anyone knows the minimum angle that was allowed, engineering wise, of an arched over bridge over a railway, i.e.. the maximum skew. I am looking to build a bridge with brick arch and stone vousoirs  with the angle of the bridge carrying a road at 25 degrees to the railway. Is this feasible on the real railway I wonder?

 

Cheers

 

Nick

[Bristol_Rich]

All in here for you...

 

http://books.google.co.uk/books?id=gZtB-RLzTw8C&pg=PA211&lpg=PA211&dq=skew+arch+angle&source=bl&ots=FoBsy70JE7&sig=YHteUTfOwuV8ouPhEXedAq2xslE&hl=en&sa=X&ei=Y21nU4PyOoKMOM38gIgM&ved=0CGAQ6AEwBg#v=onepage&q&f=false

 

If mentions "Barlae Bridge" was tested to destruction and had a 29deg so a skew would be feasible... however I would assume a road would be more likely be aligned to cross a railway as near 90degrees as possible than a railway.

[Rivercider]

Hava a look at the pictures of the Skew Bridge at Parson Street in Bristol,  

it carries the A38 over four tracks at quite an angle

 

cheers

[Orinoco]

Roads were sometimes carried over a railway on a skew by building a kind of cut & cover tunnel over the railway. The road was then built on top of the "tunnel".

 

I don't have any photos to hand, unfortunately.

[Silver Sidelines]

Hello Nick

 

Had to join in when I see the name Barlae Bridge and then read an extract from one of Professor Bill Harvey's papers!

 

I think the angle of skew needs defining - at Barlae the motor road was realigned to cross the 'Port Road' and c30 degrees seems to me be a reasonable compromise between the shortest / cheapest bridge structure and not making the road detour too long.  My purely personal view would be that an angle even as high as 45 degrees for a road would be regarded as uneconomic on the grounds that the arch would be too long.

 

From childhood there are some very interesting skew arches in the approach viaduct from Liverpool across the Mersey at Widnes - in this case the overhead railway had to cross existing tracks beneath laid to the docks - the old map suggests a very flat angle.  Perhaps someone else has a more detailed knowledge of this location.

 

Regards

 

Ray

[Captain Nick]

Many thanks for your replies and certainly the Barlae Bridge was an interesting read. We have a couple of interesting skew bridges here in Plymouth, in Devonport to be particular. One especially skewed is in what is now over the car park at Plymouth Tech College but originally crossed over the up line into Devonport Station on the old Oakhampton route. For my model I am representing a station approach road over a double track of about 35 degrees. As for the method  suggested by Orinoco above, there is a good example at Disley where the A6 crosses the Stockport to Buxton line. If anyone has any pictures of particularly long arches made necessary by skew crossings then I'd be grateful to see them.

 

Regards

 

Nick

[Highlandman]

Here are a few pictures for you to look at.

 

The first is at Rainhill on the Liverpool and Manchester line. Go to this website http://www.8dassociation.btck.co.uk/Stations/TheLM and scroll down about halfway. There is a picture taken by Terry Callaghan of a lovely stone skew bridge at the end of the platform.

 

The second one is at http://www.47soton.co.uk/2011/09/ashfield-bridge.html. And the third site is RMweb and Coachmans build of Greenfield. Here he shows construction of a skew bridge used on the layout. http://www.rmweb.co.uk/community/index.php?/topic/58427-around-greenfield-in-the1950s-standedge-route/?p=1415704.

 

I hope these links are of some use. The are also plenty of decent pictures on Google. Use 'skew arch road bridges' as a search term then click on images.

[Rivercider]

Here is a photo of the Skew Bridge at Parson Street, a look on Google Earth shows it crosses at quite an angle.

 

 

47477 passes the Skew Bridge at Parson Street with the 10.23 Penzance - Leeds 3/2/81

 

cheers

[coachmann]

Skew bridge over Greenfield railway station.....

[buffalo]

A couple of points might be worth bearing in mind here. Firstly, in rural areas most bridges carry relatively minor roads over the railway and land acquisition costs were probably low when the railway was built. Similarly, the earth moving costs for the road slopes up to the bridge would also have been quite low. Unless there were constraints such as steep slopes to one side or other of the railway, the usual solution was a minimal skew as seen in the Barlae example. There were, of course, exceptions such as the "long arch bridge" on the Somerset and Dorset just north of Midford station. Here, there was a very shallow angle between road and railway so a long bridge or short tunnel was built so that the road passed over with little change of direction.

 

On the other hand, existing buildings and land use in urban areas would make acquisition costs high and, perhaps, any necessary demolition would have been unacceptable. The Parson Street and Greenfield examples show that quite severe skews could be acceptable. btw, the angle between track and road at Parson Street is around 35 degrees (using the same way of measuring as used in the Barlae descriptions above, this would be 65 degrees).

 

Modern bridges carrying major roads are designed to keep the road straight no matter what the angle of crosing is, so very tight skews are possible. They are, however, built using quite different technologies.

 

Nick

[Captain Nick]

Thank you all for your input to this thread and also for the links to the photos etc. I have been following Coachman's Greenfield thread and his post above really shows the skew I'm after and I know it uses the same design as I'm after for my layout. I hadn't taken on board until now how much of a skew it was but thanks for taking the time to post all your thoughts.

 

Regards

 

Nick