Buildings

How Do Arches Work?

Norman arches  StewkleyThe two nearest arches support the weight of the tower. There's another arch over the window, and above it you can just see the ribs of the roof, which is in the form of two intersecting barrel vaults. A barrel vault is a long arch, like the tunnel at Gayhurst in last week's Monday photo. This is the Norman church at Stewkley.

The Monday Photo

I see a lot of arches travelling round for the North Bucks Wanderer. The last five posts have all had something to do with arches, even if you couldn’t see them in the photos.

So how do they work, and why don’t they fall down, even if they are hundreds of years old? It’s all due to the way stone, or brick, is strong.

Stone and brick are enormously strong in compression; when they are being squeezed. Arches take advantage of this, by directing the load or weight of whatever is above the arch sideways.

This is how it works. The bricks or stones around the arch are wedged shaped. The weight above them makes each wedge shape (they are called Voussoirs) try to drive itself deeper between its neighbours.

They all squeeze each other and the weight is directed around the arch and into the abutments on each side.

How arches work2

As long as the abutments (see the diagram) are strong enough to resist the weight, the arch doesn’t have to be a complete semi-circle, and some arches are very shallow indeed. This is very handy for things like railway bridges; a train won’t get over a hump backed bridge.

The red arrows show the direction of the forces involved. And yes, they do show the abutments pushing back at the arch. They have to, weird as it may sound, or they would be crushed. With arches like the ones in the photo, there are more voussoirs and they just direct the forces (the thrust lines) vertically down.

The Voussoir at the crown of the arch is sometimes bigger than the rest and called the keystone. That’s just for decoration; it’s no more important than any of the others.

Arches are very stable. Even if the foundations shift, it is likely the arch will stay up. With a simple wall, if the thrust lines stray outside the wall, it will hinge or crack around that spot and fall down. The wedge shape of the voussoirs in an arch means they will just settle into a different position.

You need at least four hinge points before an arch will fall down. You can see cracks above the big arches in the photo. Arches are great for spanning large gaps. That’s unlike stone slabs, which will just crack and fall if the gap is too big.

The first known arches were in Egypt and Mesopotamia, 5,600 years ago and were made of brick. Stone ones came later.

If you want to see a wide selection of arches here on the North Bucks Wanderer, look for churches or bridges in the categories in the sidebar.

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The Monday Photo

Norman arch

Booking the Chapel

This is the oldest building in Buckingham, but it’s not as old as you might guess, looking at the doorway. This is the Chantry Chapel, on Market Hill.

It really is a genuine Norman doorway and not some later imitation, but the building dates from a rebuilding in 1471. The original building was built as St John’s Hospital for the Poor and Infirm in the late twelfth century, and I suspect that the doorway dates from then.

It’s a pretty typical example of Norman masonry; the semicircular arch has several concentric rows of decoration, and the outermost rows are supported by a small column on each side.

The hood mould, the outermost row that directs rainwater around the door, is carved in a sort of double nailhead pattern. Each nail head is pyramid shaped and you might have seen actual nail heads like this in ancient doors. 

The next row is perhaps the most well known and common pattern, the chevron or zigzag. If you recognise nothing else from Norman times, you’ll have seen this pattern before.

The next row is plain, and the arch is all the better for it. The innermost row is carved with shallow pointed-arched arcading. On the inside face of this last row, you might be able to see a groove running all the way round the arch. Any rain that got as far as the last row and tried to slip in would be defeated by this groove.

This doorway may well be in its original position, and the chapel, sometimes known at the Old Latin School, was just rebuilt around it.

So why is this the oldest building in the town? There’s a couple of reasons. Churches are often the oldest local building in a town or village but Buckingham’s old church collapsed, not for the first time, in 1776. This time it was not rebuilt. A ‘new’ church was erected in a different spot.

And in the early 18th Century Buckingham had a disastrous fire which destroyed  much of the town centre, and many older buildings were destroyed.

But the Chantry Chapel has had its problems too. Three times over the centuries it has needed major work, and today is looked after by the National Trust. No longer a chapel, it’s just about my favourite sort of shop; a second hand book shop.

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The Mill on the Hill

Post mill  BrillThe mill faces into the prevailing West wind.

There used to be two windmills at Brill. The second mill, actually the first to be built, took a lightning strike in 1905 and had to be demolished the following year. The two mills made a nice pair, both being post mills.

Post mills have a massive centre-post around which the entire mill rotates to face the wind. At Brill, the centre-post was about two and a half feet square at the base, and rounded above, tapering to 17” diameter at the top. The post has to be strong enough to hold the weight of the mill, together with the great pressure of storm winds, high up on the hill.

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The Monday Photo

Behind the Green Man

This pub is on the Market Square, Aylesbury. It’s not particularly old or noteworthy, but for many years if you wanted entertainment, through the arch on the side of the pub to the building that stood behind it was the place to go.

At different times over the years there you could see performers like Genesis, The Who, Roxy Music, David Bowie, or Ronnie Barker, or even watched a film.

The Green Man  Aylesbury

There’s been plenty of live music. Ronnie Barker might not have sung on stage there, but like David Bowie, there’s a statue of him in the town.

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Looking Up, At Aylesbury

Aylesbury is like most towns we go to; we walk through the streets and never look higher than the ground floor. And we miss everything.

Here’s just a few of the things we can see around Aylesbury’s Market Square, if we just look up above the shop fronts.

The Dark Lantern  Aylesbury

I first knew this building as The Dark Lantern pub, but it hasn’t been called that for quite a while. It is now a nightclub called Pulse 51, that’s also a live music venue featuring rock acts. This means it can’t open during lockdown.

You might not notice as you walk past it down the cobbled alley into Silver Street (far right), but look up and you’ll see this is a 16th or 17th Century timber framed building.

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The Mill on the Hill

Quainton windmill

The Monday Photo

This is the tallest windmill in Buckinghamshire, and it’s at Quainton. The mill sits at the top of the village green, but it’s still 150 feet, or 45 metres, below the crest of Simber Hill on the North side of the village.

That’s why Quainton Windmill is 65 feet, 19 metres tall; so it can catch the North wind as it comes over the hill. This is the third tallest windmill in England.

By the way, Simber Hill is really just part of the great mass of Quainton Hill. The actual summit of Quainton Hill is another 110 feet or 34 metres higher, and half a mile further North.

Construction of the mill started in 1830, but a few years later the owners installed a steam engine into the base of the mill, so grain could be milled on calm days. This was a common ploy then.

There are photos of the mill in working order in 1860 and 1870, but a 1900 photo shows it to be disused. The fantail, red and white in the photo above, had been blown off the year before during a gale. The mill lay derelict through two World Wars and for decades after. Then in 1972, restoration began.

Work went on for years until grain was milled for the first time in nearly a century in 1997, but more work still had to be carried out. I remember it all working when I visited a few years ago, but I later heard that the mill was out of action again.

It’s now back in working order. Just over a year ago the sails were hoisted back into position after they had undergone a six year refurbishment project.

Once we’ve overcome the Coronavirus, we can visit the windmill again. The usual opening times are 10 am to 12:30 pm, every Sunday.

There’s a pub on the green, The George and Dragon. In normal times it’s open until 2 pm on Sundays.

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