25 June 2011

Twisted Pillars

This animation shows the construction of a twisted brick pillar, 440 by 440mm and offset by 10 degrees

Due to the lack of plumbing points, it can sometimes be difficult for beginners, to keep such spirals absolutely up-right

One method is to use triangular templates and rest these on the corners

A better method is to use a timber-board, cut to the right shape, and threaded onto a central steel rod, see diagram


Image from Bricklaying
by Cartwright, pg 268
Calculating the offset angle


Offset at 20°, shaded
Although an angle of 20° would make the pillar twist round quicker, there are some design issues

Not only would the frog be seen, but the offset at the corner is over ¼-brick

This makes the structure behave like corbelling and
it is likely to become unstable


Usually, oversailing is no more than 28mm, which means reducing the angle
of twist, and so increasing the number
of brick courses, before the pillar turns
a full circle

10° is often used, since this gives nine courses for a quarter-turn

The black and white photo shows the twisted chimney at Buckingham

It was built over 500 years ago!

Image from:A History of English Brickwork
by Nathaniel Lloyd, page 341

More recent examples are shown below...


Twisted pillar in America
Image from wemasonry.com

Twisted pillars in India
Image from Design flute.com
...and this one is even better!


Twisted Arch in Wales
Image from Follies.org.uk

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