31 August 2014

Lancashire Bridges: 3. Penny Bridge, Caton

This bridge spans the River Lune midway between the two former railway bridges in my last post.

Built in 1883, it comprises three elliptical sandstone arches. The roadway is level, with straight balustraded stone parapets either side.

The road originally crossed the river here at a ford, until a privately funded bridge was built in 1805. Like the present bridge, this had three elliptical stone arches. A penny was charged as the toll for the use of the bridge. As of 1880, the bridge was badly deteriorating, and the County Council took over the bridge, building the new one for £8,500.

The bridge was designed by the Lancashire County surveyor, with local architects E.G. Paley and Hubert Austin, and is now Listed Grade II. The builders were Benton and Woodiwiss, a Derby-based firm, who were also extensively involved in railway construction.

This bridge just leaves me with questions: why is the roadway level, when a curved alignment would have looked much better? Why are the parapets solid over the piers and only balustraded over short lengths over the arches?

Further information:

28 August 2014

Lancashire Bridges: 2. Crook O' Lune Railway Bridges

I'm featuring a few bridges on the River Lune, working downstream towards the see. Most of these are readily accessible from a cycle trail, the Lune Millennium Cycleway, which runs along a disused railway line between Caton and Lancaster, indeed the first two bridges, at Crook O' Lune, carry the cycle trail itself.

The two bridges were built around 1880 and carried the Midland Railway (formerly the "Little" North Western Railway) across a long U-shaped bend in the river. The railway line was closed to passengers in 1966, and dismantled in the 1970s. Both bridges are Grade II Listed.

I have seen the bridge design credited to Edmund Sharpe, but there seems to be a discrepancy with dates. English Heritage list the bridges as being in the 1880s, but Sharpe's involvement with the railway line dates from when it was first constructed in the late 1840s. If anyone knows anything more, please post in the comments.

Both bridges are essentially identical, consisting of a number of wrought iron arch spans supported on sandstone masonry piers and abutments. The choice of material may explain the discrepancy in dates. The shape of the arches seems to indicate cast iron, but closer examination shows riveted construction. Perhaps cast iron spans were replaced in wrought iron?

Whatever the case may be, these are fine bridges.

The east bridge was extensively refurbished in 2013 at a cost of between £1m and £1.5m.

Further information:

26 August 2014

Cumbria Bridges: 12. Devil's Bridge, Kirkby Lonsdale

This is one of several bridges I visited back in May, all around the border between Cumbria and Lancashire, and all of which span over the River Lune.

"It is by far the finest bridge in the north of England", wrote Edwyn Jervoise in 1931. Like the similarly ancient Twizel Bridge (in Northumberland), it is a ribbed arch, a type I always find visually attractive. It is a Scheduled Ancient Monument, and a very handsome structure.

The bridge dates to the 13th or 14th century, and as with many other structures around Europe, it was reputed to have been built by the Devil. An old woman made a deal with the Devil for him to build the bridge in return for the first soul to cross over. She then tricked him by throwing bread across the bridge so that her dog ran over it first. The story is recounted in more detail in George Bernard Wood's book, Bridges in Britain.

There are many variants on this tale for the many so-called Devil's Bridges, suggesting that the poor fellow struggled to learn any lessons from being repeatedly tricked.

Further information:

24 August 2014

Yorkshire Bridges: 5. Scammonden Bridge

This is the last, and largest, in a set of Yorkshire motorway bridges which I visited earlier this year.

Spanning 125m, it is the biggest concrete arch bridge in the UK. It carries a local highway across the motorway where it passes through a huge cutting. In some photographs, Scammonden Bridge can appear almost "small", as it is scaled appropriately to its setting.

Its sheer size becomes more apparent only when passing underneath. A construction photo from 1969 showing the scaffolding used to erect the arch also gives a much better idea of quite what an enormous structure it actually is.

The concrete arch comprises a twin-cell reinforced concrete box section, supporting slender spandrel columns. These are hinged at the top to allow thermal movement of the deck to take place. The deck is built from conventional precast, prestressed concrete "T" beams.

As with the other bridges I visited in the area, this structure was designed by the West Riding County Council. Sri Sriskandan was credited with a key role in an obituary published by the New Civil Engineer.

The bridge provides spectacular views along the motorway and onto the moorland that the road bisects. It's startling to try and imagine this setting before the motorway was built, as the huge "valley" that the road passes through is entirely artificial.

The bridge seems to be in generally good condition, with the notable exception of the parapets, which are in serious need of repainting.

Aesthetically, it is appropriate to the place, and generally well-proportioned. The only "wrong note" is the way that the profile of the arch at its crown cuts into the deck profile, but this is a minor matter.

It would be fascinating to see what kind of bridge would be built today if a new motorway were built in the UK requiring a similar span. However, it's hard to imagine such a road being allowed to be built, given the visual impact on the rural landscape.

Further information:

28 July 2014

Yorkshire Bridges: 4. Needle Eye Bridge

Okay, I'll continue this series of posts a little further north along the M1 Motorway. I'm bypassing the Cock Inn Bridge simply because it proved impossible to get a decent photograph, which means the next bridge of interest is the Needle Eye Bridge.

This is a three-pin concrete arch "accommodation bridge", built to carry farm traffic and pedestrians. The arch spans 88m between springings, and was cast entirely in-situ in reinforced concrete.

It seems to owe more than a little to Robert Maillart's 1933 Felsegg Bridge, the first of the Swiss designer's concrete arch bridges to adopt an angle at the upper hinge rather than a continuous curve. This is a departure from pre-conceived notions of what an arch should look like, and is structurally more rational, responding appropriately to the full envelope of possible live load effects. Needle Eye Bridge lacks the sharp angle at the crown of the arch, but overall the bridge is shaped in a similar manner.

It is better than Maillart's bridge, however, in its use of prestressed suspended side spans, preserving a simple, clear geometry. Maillart's designs paired the solid main span with finicky, slender approach structures, often over-fussy in their detailing.

My sense is of a design team very aware of precedent, and enjoying the rare opportunity to experiment with form.

As with the other two M1 bridges I featured recently, at Droppingwell and Smithy Wood, I find it amazing that this bridge is not protected by any kind of heritage status. Sure, it only dates to the 1960s, but the whole set of bridges along this part of the motorway, designed by the West Riding County Council, is remarkable and worthy of wide recognition.

Further information:

26 July 2014

Pedestrian Bridges of London: A Short Guide

Updated 27th July 2014 - THIS OFFER IS NOW CLOSED (see below)

I mentioned this little booklet recently. It was given free to attendees at the recent Footbridge 2014 conference in London. It is based on (much shortened) articles about significant footbridges in London, with all text and photos contributed by The Happy Pontist.

There are twenty pages, covering the following bridges: Bridge of Aspiration; Challenge of Materials Footbridge; Millennium Bridge; Golden Jubilee Footbridges; Chelsea Bridge Wharf Link Footbridge; St Saviours Dock Bridge; Royal Victoria Dock Bridge; South Quay Footbridge; West India Quay Bridge; Plashet School Footbridge; Stratford Town Centre Link; Green Bridge; Rolling Bridge; Merchant's Square Footbridge; Sackler Crossing; Xstrata Treetop Walkway.

The booklet also provides some (very) brief details on significant bridges and structures encountered along the River Thames, the conference's Gala Dinner boat cruise route.

I have eight of these booklets left over from the conference, and I will post them to the first people to email me (happypontist at gmail dot com), having first made a donation to Bridges to Prosperity. I wrote about B2P and their excellent efforts to build low-cost footbridges in the developing world, way back in 2009.

The booklets will never be reprinted, so this is a unique chance to get a copy.

It's very simple:
  1. Donate to B2P whatever amount you wish, although an absolute minimum of US$5 please.
  2. Email me your address and a copy of your B2P donation receipt - if you want to keep any details private, just take a screenshot and cut out any private bits.
  3. This is a bit silly since I blog anonymously, but I will sign the booklet on request. Minimum US$10 donation for a signed copy.
  4. I will post you a copy of the booklet, free of charge. Please bear in mind that I am covering international postage when you decide how much to donate to B2P!
  5. I will post here when all copies are gone, but there can be no refunds - if you donate, and I've run out of copies, never mind, at least B2P will benefit!
  6. Did you attend the conference and already have a copy of the booklet? That's great, but please consider donating to B2P anyway, they're a great organisation.
Updated 27th July 2014 - THIS OFFER IS NOW CLOSED

All the spare booklets are now allocated, many thanks to those who have donated to Bridges to Prosperity! I have also made a donation myself, and together we have raised US$350 to support their excellent work around the world. I'm absolutely delighted to have helped create this opportunity.

24 July 2014

Yorkshire Bridges: 3. Smithy Wood Footbridge

I first became interested in the Smithy Wood Footbridge when Tallbridgeguy posted about it on his blog.

It's another great example of how the West Riding County Council engineers in the 1960s applied real innovation to deal with a specific technical challenge. Their concern when designing new bridges over the Sheffield to Leeds motorway was with possible mining subsidence, which could lead to foundation settlement and severe damage to their new structures.

Three new footbridges were designed as concrete Wichert trusses, possibly the first such designs in concrete, and almost certainly the first such designs in Britain. Only one now survives, the footbridge at Smithy Wood. The concept, originally developed by E.M. Wichert in Pittsburgh in 1930, is for a bridge which is statically determinate but also continuous, such that pier settlement can occur without causing damage.  It achieves this by incorporating a quadrilateral bay within the truss immediately above the support pier or piers.

Don't ask me quite how that works: any first-year structural engineering student will look at it and ask why the quadrilateral truss bay doesn't simply "squish". I look at it and I don't really know why either, although I think it has something to do with the feasible displacements of the two adjacent spans. To make it work, the designers had to undertake basic research and testing for the tri-hinge, the point directly above the pier. The upper hinge also has to be prestressed.

It's interesting to think that engineers of the time were designing structures with hinges partly to deal with settlement but also to make them determinate and hence amenable to analysis. Today's engineer would struggle to analyse this bridge: modelling it in any conventional structural analysis software would be fruitless, as the quadrilateral bay will be treated as a mechanism and the software will just output an error and come to a halt.

The bridge looks to be in much worse condition than it really is. It looks like it had a concrete coating which is now peeling away.

Perhaps the thing I found the strangest about this bridge is not its supremely odd structural system, but its incongruity. One end of the bridge is terminated with a series of switchback ramps. This gives the bridge a very urban feel, it's the sort of arrangement you often see in an urban environment. But at Smith Wood, it's in the middle of a field, and it seems completely out of place. This is probably what I liked most about the bridge ...

Further information: