Index

18 May 2011

Pitman's Vol 14 - Rough and Relieving Arches


Front Cover of Volume 14
Building Educator
Volume 14


by R Greenhalgh (Ed)

Published by Pitman & Sons Ltd
16th April 1927

No ISBN number

Extract from page 649
Rough Arches
These are constructed of uncut bricks, usually built up in concentric rings half a brick thick, the number of rings varying with the span of the opening

The only connection between each ring is the collar joint of mortar


Lacing Courses in Arch
Image from Chest of Books

In arches of very wide span, the different rings are often bonded to each other by inserting some stretchers

These are called lacing courses
The reason for using headers is to reduce the size of the mortar joint. It will be seen that when the voussoirs of an arch are not cut wedge-shape, the necessary radiation can only be obtained by a thick joint at the outside curve

For arches of sharp curvature, the use of 9" rings would result in excessively wide joints

Relieving, or Discharging Arches
Rough arches of small rise are used to relieve the weight above the heads of door and window frames, or over interior openings that have been spanned by timber beams

In constructing these arches, care should be taken to see that no actual load is permanently transmitted to any place other than the abutments of the arch


Rough Relieving Arch
Fig. 58 - Volume 14 page 651
The method of construction is to form a curved surface of rough brickwork called a core, cut approximately to shape by a wooden mould, which is tacked onto the lintel

A layer of sand is then spread to the correct curve, and the arch is built with its soffit resting on the sand, the skewback being formed clear of the ends of the lintel

When the bedding material, with which the arch has been built, has properly set, the sand is raked out, ensuring that the whole of the weight resting on the arch is being carried by the abutments

Thus, in the event of the lintel being destroyed, either by fire or decay, no settlement of the brickwork would take place

Plain Arches
Arches constructed with uncut bricks are frequently used with good class facings on elevations of some importance. In such cases they are called plain arches

They are usually arches of simple curvature, such as relieving arches over a series of small openings which
are spanned by stone lintels

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