Railway  Bridges

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Railway trains come in many colours, with a variety of electric, diesel electric and steam locomotives. What they all have in common is that they are heavy, they don't work well on gradients, and they don't work well with sharp curves in the track. So when you go to a town with a railway station, you are likely to find level crossings and bridges, often with the road dipping down to provide headroom. Nothing wrong with that, until a heavy downpour occurs, and then you find out that the drains have become clogged up since the last downpour.

Because of its stiffness in three dimensions, and the cost of bridges to take the heavy weights, a railway is liable to divide a town. The phrase "wrong side of the tracks" will be known to many who live in such a place. Motorways and other large roads are almost as stiff, but usually cut a wider path through everything they meet. Both railways and large roads can be found in cuttings, where at least they are a little less noisy, or on embankments, but even when they are on ground level, their effects are about the same. Canals are stiff for a different reason: they have to follow the contours if expensive, time-wasting and water-wasting locks are to be avoided.

Several pages in this web-site discuss these effects, for example - Foot bridges and Town bridges. There is also a page about railway bridges over the river Severn. These pages include examples of the main types of railway bridges that were built in the 19th century - masonry spans, plate girders, and, to a lesser extent, trusses.

If you make a journey on an English country road, you may make all manner of detours, sometimes even around three sides of a rectangle. Such weird alignments probably date back to times when the rich and powerful could refuse access to their land. When journeys could take all day, a few detours may not have been as annoying as they now appear to be, when we expect to drive at 70 mph for most of a journey. Improvement of a section of road leads very soon to demands for elimination of bottlenecks, which are, of course, sections that did not stand out as problematic before.

The successive advent of canals, railways and motorways could not take place while people could refuse access, and government took powers, through acts of parliament, to acquire the needed land.

The page about town bridges is concerned mainly with the bridges of Gloucester, a city of fairly average size, on ground that does not slope steeply at any point (unless you are on a bicycle). In contrast, the pictures below show railway bridges in Stroud, a much smaller town between Bath and Cheltenham. Stroud lies at or near the confluences of several deep valleys in the Cotswolds, and lies on the railway line that connects Swindon to the main line from Birmingham to Bristol. Building this line through the Cotswolds required the building of many bridges, and a tunnel or two. It was not cheap, and much of the line is single track.

StroudArchA.jpg (115957 bytes)  StroudArchB.jpg (113787 bytes)  StroudPlateA.jpg (93604 bytes)

If you drive through Stroud on the A46, you will notice the high arch bridge. Already at this point, the railway has begun to hug the high ground in preparation for the Cotswold crossing. Most of the arches are hidden by buildings, and as with so many of these bridges, they shelter now derelict workshops and garages. The second picture shows that all the piers are themselves pierced by arches, saving on material and perhaps reducing the chance of cracking if anything should shift. As Maillart discovered, less is often better. The third picture shows the railway crossing a street, the high retaining wall and the bridge creating a dark passage. Both types of bridge are common throughout England. Often they are in a shabby condition, with rust, peeling paint, stalactites and other flow products disfiguring their spans and walls.

Near the big railway bridge, a footbridge attempts to overcome the problem of crossing the busy A46 on foot. It illustrates, very clearly, the difficulty of providing pedestrian access to a high bridge in a confined space. In fact both steps and ramps are provided, the ramps forming long zig-zags, not to difficult to climb, but tedious in the waste of time they require. But for a person with a child's buggy, or for an old person, that is the only way. The ramp on the left does not continue the line of the main span, which detracts a little from the appearance. Ground level is reached by three ramps, so for those in a hurry, a steep stairway is provided.

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If you want to escape the noise and bustle of a town, go to the railway station.  Here are some pictures of Stroud railway station. In earlier times, the silence would occasionally  be broken by the arrival of a terrifying, smoking, sulphurous, clanking locomotive. After it had gone, the silence would be deeper than ever.

StroudStationA.jpg (88135 bytes)  StroudStationB.jpg (106969 bytes)  StroudStationC.jpg (120600 bytes)  StroudStationD.jpg (77441 bytes)

The cantilevered roofs, reaching out past the edge of the platform, protected passengers from the weather until they were safely on the train. How do you think these roofs are anchored in the building? The modern equivalents are the trunks that take you to the door of an airliner.

StroudBrunel.jpg (65943 bytes)Shunters.jpg (83145 bytes)It's almost impossible to think about the Great Western Railway without thinking of Isambard Kingdom Brunel, though the locomotive designer Daniel Gooch should be remembered too. Brunel's ambition, imagination, obstinacy, and unwillingness to delegate, sometimes tended to derail his projects, and to cost the shareholders dearly, but his brilliance is not in doubt.

Not too far from Stroud is Swindon, where many GWR locomotives were built, the last being the Evening Star. In the Railway Museum you can see a replica of the magnificent North Star. Unfortunately, the original was destroyed after its useful days were over. What would a museum of today's achievements look like? Row upon row of almost identical integrated circuits? Walls covered with listings of software? The fact is that museums cannot give the whole story. Even in a railway museum you will find little about the thermodynamics, the metallurgy, the fabrication techniques, and the sheer hard work that went into the railways.

Much railway building took place in an era when the most suitable materials were not yet known. Engineers, for a long time, had to make do with wood, stone, brick and cast iron. Excellent though these materials are, in the right places, there are things you cannot do with them. Opening up the United States to railways required large numbers of cheap bridges, and many kinds of truss were invented. Until wrought iron became available, there were many problems, and not a few disasters. Brunel, too, had to face financial problems in Devon and Cornwall, where the incised landscape required many bridges and viaducts. The problem, as always, is building before the money has come in from the travelling public. One of Brunel's solutions was to build timber spans, often on masonry piers. The spans were designed in such a way that timbers could be replaced easily when they started to rot or crack. The idea was to build cheaply, and replace the cheap by the durable when the cash flow allowed it.

M25ArchesFebA.jpg (80391 bytes)Here is a railway viaduct across a wide valley. The arches were wide enough for three lanes of the M25 motorway to pass through.

The communication age is built on algorithms for computation, compression and expansion, encoding and decoding, error-detection and error-correction, multiplexing and demultiplexing, and many other ingenious techniques.  These are not easy to understand for the layman, and perhaps unlikely to be commemorated in museums.  But the spirit of ingenuity is the same as it was during the 19th century. 

And the connection with the 19th century is closer than you might think.  The laws of thermodynamics have been summarized as follows.

You can't win: you can only break even.

You can only break even at absolute zero.

You can't get to absolute zero.

So your refrigerator and air-conditioning system not only pump heat from where you don't want it, out into the atmosphere, they also pump out energy that came in from the public energy supply.  

What has this do do with communication?  It turns out that the laws of communication are surprisingly parallel to the laws of thermodynamics.  As in thermodynamics, there are reversible processes and irreversible ones, though we must be careful not to take the analogy too far.  Making a JPEG is an irreversible process, because it throws away information, leaving an approximation to the original.  Many audio and video systems reduce bandwidth by throwing away information that the average person cannot detect among the dominating signals.

Returning to the mechanical systems of the age of railways, have you ever wondered how people created the first accurate screws and nuts, lathes and milling machines, where none existed before.  How do you build up accuracy from inaccuracy?  We don't need to know about information theory to know that this was a tricky problem.  Think about it.  How would you make something that is ten times more accurate than anything that exists?  And how would you check it?

Earlier, we mentioned Swindon, where all that remains of the GWR is the railway museum and a railway worker's cottage.  The railway works were enormous, and even now, a long road tunnel under the tracks reminds us of their extent.  Swindon was divided into "Old Town" and "New Town", but the railway and works divided New Town just as effectively.

Those who have been in those works while they were still operating cannot forget what they saw and heard.  The noise in the rivetting shop, so intense that you could not hear yourself shout.  Not in bursts, but continuous, all day, every day.  The steam hammer, controlled by a man with a simple lever, silently bouncing a twenty ton steel hammer on a trampoline of steam to amaze the children.  The mighty driving wheels, small compared with those of Daniel Gooch, but impressive enough, even so.  The massive axles.  The huge chassis of the locomotives.  It all came together in a giant machine that roared into the station, fascinating and frightening the children at the start of their holiday.

Every parent had to have pennies ready when the holiday began, because on the station there was a massive cast iron machine, with a big dial showing all the letters of the alphabet, and a long pointer.  For one penny, you could produce a metal strip bearing your name in embossed letters, to replace the one you made last year, and lost.

Everyone "knows" that the industrial revolution began in England, but this phenomenon obscured the fact that leadership in science was already passing to other countries.  If you make a chart of important scientific discoveries, by country, from 1600 to 2000, you might, if English, be surprised by the results.  The first steam engines were almost unimaginably inefficient, and their fuel consumption would horrify the even the least "green" of people today, not to mention economists.  The science of heat and thermodynamics was unknown.  Do you know at what date the law of conservation of energy was finally established?  What about the other laws of thermodynamics?

Those early engineering pioneers had to work with very primitive knowledge and understanding, yet they achieved tremendous results.  Do you know when the law of conservation of energy was finally realised?  

Here is a very good book about early railway pioneers and other engineers.  It's people, not formulas, that get things done.

Sweat and Inspiration - Pioneers of the Industrial Age

Martin Worth     Sutton Publishing     ISBN 0-7509-2675-9

Town bridges    Severn railway bridges 


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