From  Arch  to  Zither

Arches, bicycle wheels, cembaloms, chimneys, dams, domes, harps, 

pianos, scrums, tennis rackets, tunnels and zithers.

See also - How Arches Work - Arches Two - Arches Three


Very small arches

Larger arches

Niagara Falls bridge

Bridges of Paris

British Arches


Lune arch

Severn arches

Telford's arches

How arches work

From beam to arch

Outward thrust

Natural arches

Hinges or pins

Arches, beams and frames

Line of thrust - funicular

Propped beams

Thrust and sagging


Box Girder    

Cable Stayed    





Severn Arches     

Arch Varieties    

Musical Arches

Arches in secular buildings    

Arches in religious buildings


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.  arch bridges 1

Imagine a grotesque animal with legs sprouting in all directions, but with no apparent head. It seems to be engaged in a futile struggle within itself, sometimes making convulsive movements in seemingly random directions. What is it? It's a rugby union scrum. Sixteen people push with thirty-two legs, each half trying to push the other half back. If fifteen of the people could be instantly removed, the remaining one would fall to the ground. You don't need to be a student of Zen to know the answer to half a scrum. One half cannot stand without the other.

Sometimes the scrum is almost perfectly balanced, at other times one side can push the other back. The scrum can even turn, which is not allowed, or it can be made to collapse, which is dangerous. What keeps it up? The heads and shoulders of the players push forward, and their weights pull down. These forces are resisted by the upward and forward push of the ground. The scrum is a living arch, and it demonstrates all the principles of that structure. It exerts a weight on the ground, and it exerts outward thrusts, resisted in this case by friction.

SevilleA.jpg (34419 bytes)The cathedral of Seville, with its double row of buttresses on each side, is the structural equivalent of a scrum, with the two sides of the nave corresponding to the two front rows, and the two rows of buttresses on each side corresponding to the remaining two rows of players on each side.

Another living bridge is the case of a climber bridging across a wide chimney. In this example, her or his weight is resisted by the vertical friction that is generated by the outward force on the walls.

.  arch bridges 2

The problem

Here is the problem - how to get a road across a river. 

Ford.jpg (32473 bytes)

The small river running from left to right in the picture is the river Windrush at Upper Slaughter, in the Cotswolds.

The solution

Cotswold1262.jpg (111093 bytes)The simplest solution, shown above, is a ford, and as this river is normally only about 15 cm deep, a ford is adequate, if you drive slowly. On this occasion, however, the river was much deeper after heavy rain, almost covering the openings of the small two-arched footbridge on the right. The picture at left shows the bridge with a lower water level.  Fords are only useful for small, shallow, slow-flowing rivers. Sometimes, in time of flood, water flows across roads or even bridges. Vehicles can be borne away by the water, which has lifting power that is astonishing. Remember that one cubic metre of water weighs one tonne, and that the lifting and carrying power of water doesn't just double when the water goes at twice the speed - it increases much faster than that.

Ford7Hampton.jpg (104122 bytes)SevenhamptonSmall.jpg (271383 bytes)Here is another ford, about a kilometre from the source of the river Coln, flowing from right to left. Again the pedestrians can use a small bridge. The second picture, a typical Cotswold view, shows a part of the nearby village of Sevenhampton.

The real answer is commonly a bridge, and rarely a tunnel, though ferries are still found. It is rare for a road to pass under a river, though aqueducts, including some famous and large ones, carry canals over roads, railways and rivers.

RampJ.jpg (110714 bytes)What about this "ford"?  It has only one side.

RampJB.jpg (66221 bytes)The answer is a boat, as I K Brunel realised during the 19th century. He imagined people travelling from London to Bristol by train, and then boarding a huge ship to travel to New York. The idea of integrated transport systems was sound, but the technology was not there at the time. Brunel did design three revolutionary ships, but economic and technical considerations got in the way of success. For completely different reasons, Bristol was associated with another transport failure during the 20th century - the Bristol Brabazon airliner.

.  arch bridges 3

Some  Very  Small  Arches

Arch1.jpg (48254 bytes)BrickArchHG.jpg (82726 bytes)The arches in the first picture, over the River Windrush at Barton, near Guiting Power, in the Cotswolds, must represent about the smallest size of arch that was worth building. In fact they are culverts rather than bridges, carrying the river under a minor road.  Nowadays the bridge might be built another way, as in the examples in the panel below. Notice the deformation from the original semicircular shape. The other picture shows a similar construction in brick. Notice the voussoir (sector) that has moved out of position.  We already learn something about arches. They seem to be quite stable when deformed.

ArchTinyUU.jpg (117860 bytes)Here is another small arch.

ArchSmallKT.jpg (68608 bytes)AbingAK.jpg (56981 bytes)Here are more examples which have been constructed as pipes.

.  arch bridges 4

Arch2.jpg (44397 bytes)  AbbeymeadGL.jpg (32768 bytes)

The small arches in these pictures are based on tubes made of corrugated metal. Plenty of space has been provide for extra flow in times of spate. The ends are faced with reconstituted stone, which has not been arranged to look like arches - just layers of "blocks". Whether structures should be made to conceal their workings is an interesting subject for discussion. If one function of a structure is to look pleasant, then it may not be obligatory that its structure and technical workings should be obvious at the expense of appearance. In case, in a real structure, foundations and pre-stessing cables are never visible, for example.

A bridge that looks like this appears in William Hogarth's satirical frontispiece to Dr Brook Taylor's Methods of Perspective. The picture includes not only ridiculous examples of wrong perspective, but a bridge that could not stand up. David Hockney copies the bridge in Kerby (After Hogarth) Useful Knowledge. Hockney has pointed out that the errors in perspective can actually create space, just as correct perspective does, but differently. So both Hogarth (with the bridge) and Hockney (with the perspective) remind us how very differently the artist and the engineer look at the world. In both pictures, the layered blocks resemble those of a "corbelled arch" (not an arch at all), described elsewhere.

After all, stressing wires are seldom visible, so the observer cannot see true nature of a structure which uses them. And foundations are never visible.

A pleasant feature of both arches and suspension bridges is that their structure and function are fairly clear, in combination with an attractive form. The great importance of appearance is emphasised by Fritz Leonhardt in his book "Bridges".

M5CL.jpg (111108 bytes)CorrugSX.jpg (63581 bytes)A similar construction takes a brook (left picture) under a slip-road of the M5 motorway. You might think that this is a fairly simple thing to construct, but when you go into the tunnel, which is about fifty metres long, you find that large piles of stones have been placed along the stream on alternate sides, making artificial meanders which reduce the speed of flow in times of flood. Even the simplest project requires thought about possible future events. The bridge in the right hand bridge even has a road under it as well as over it: it allows access to a large car-park.

.  arch bridges 5

HorsebereY.jpg (68455 bytes)HorsebereW.jpg (80070 bytes)HorsebereV.jpg (42534 bytes)Further upstream, the brook is crossed by the link road from a business park to a bypass and a motorway, over an arch based on curved concrete slabs. The use of a slightly non-circular profile increases the headroom over the farm track and the footpath. Although this bridge is seen by a relatively small number of people, the designers have achieved a very pleasant appearance. At the other end of the tunnel, a wooden beam footbridge crosses the brook.

.  arch bridges 6

This picture shows the bridge carrying the B4425 road over the river Coln at Bibury in Gloucestershire. This is definitely a real bridge, even having small cutwaters.  

Bibury.jpg (103878 bytes) There are many such bridges, of varying sizes in the Cotswold region, usually made, like this one, from Cotswold limestone. Other regions of Britain have bridges made from their own local stone.

.  arch bridges 8

Some  Larger  Arches

Arches vary enormously in appearance, as the following pictures show. Some of the variables are - 

Length of span

Width of deck

Height above ground or water

Height of piers

Ratio of span to width of pier

Ratio of span to rise

Number of spans


Segmented or curved

Type of construction

Norman.jpg (68311 bytes)  Cize.jpg (40648 bytes)  AlpViaZ.jpg (343209 bytes)  AlpineViaductR.jpg (119044 bytes)  Monnow.jpg (50566 bytes)  Devils.jpg (75909 bytes)

Arch  at  Niagara  Falls 

Niagara2.jpg (59495 bytes)     Niagara1.jpg (16123 bytes)

Bridges  of  Paris

Paris1C.jpg (15288 bytes)Paris3.jpg (14897 bytes)The arches of le Pont des Arcs are very unusual. They appear to support the footway only at the half-span and quarter-span points, while requiring support themselves from the piers.

Orsay1.jpg (120159 bytes)This is a part of the Mus ee d'Orsay in Paris. This wonderful building was once used to house a railway station.

Val d'Herens

Arolla.jpg (187511 bytes)This is a short tunnel, rather than a bridge, but it is a neat solution to a problem. Will the solution outlast the problem?

.  arch bridges 9

Some  British  Arches

Links to other arches in this website - Lune Arch  Severn Arches  Telford Arches

Bradford.jpg (32393 bytes)This is a very old bridge at Bradford-on-Avon, near Bath. This bridge, like the towns of Bradford and Bath, was built from Cotswold limestone, which is attractive, but susceptible to sulphur in the air.

Pulteney1.jpg (63629 bytes)Until Bath was cleaned in the 20th century, many of the buildings were almost black. The Pulteney bridge, built by Robert Adam between 176 and 1774, over the Avon at Bath has shops along both sides.

BWArch1.jpg (42455 bytes)This bridge has two rows of very small voussoirs. There seems to be a concrete arch above them.



M42ArchU.jpg (31904 bytes)An elegant footbridge over the M42 motorway south of Birmingham. Is there a hint of Maillart?

BrumBroadSt.jpg (190153 bytes)And in Birmingham itself, here is Broad Street canal bridge.

RABridge1846S.jpg (231998 bytes)Click here to read about the Royal Albert bridge at Saltash, a unique arch bridge.


BohinjArchA.jpg (98509 bytes) BohinjArchB.jpg (89978 bytes) BohinjArchC.jpg (107493 bytes) BohinjArchD.jpg (99836 bytes) BohinjArchE.jpg (149524 bytes) BohinjEast.jpg (351116 bytes)

Here is the bridge across the Sava Bohinjka at the eastern end of the beautiful Bohinjsko Jezero in Slovenija. The church is that of St John.  It includes 14th century frescoes and is well worth seeing. The bridge has pedestrian refuges at the centre, and the wooden posts in the river bed are probably the remnants of defences against scouring in times of flood. After a heavy downpour in the Julian Alps, the river can rise rapidly, with an enormous increase in the rate of flow. Unfortunately these rather poor pictures don't do justice to the scene. In the sixth picture, you can see, at the eastern end of Bohinjsko Jezero, the same bridge and church.

Some Technical Terms

ArchDrawn7Oct2A.gif (10796 bytes)Sometimes in books about architecture you see technical terms about masonry arches. Here are some of them - archivolt, coping, dentils, extrados, haunch, impost, intrados, parapet, pilaster. You probably don't need these, but the diagram at left may be useful to explain the use of others. There are also numerous types of masonry arch - convex, curtain, elliptical, horse-shoe, lancet, ogee, round, segmental, shouldered, trefoil. tudor. Again, you probably don't need these names unless you have a specific interest in architecture. For other types of span you may come across fewer specialist words, one reason being that they are less frequently used in architecture, another that they were much more recently developed.

Toscana.jpg (59541 bytes)

Elegance in Toscana

Continuation - How Arches Work