Front Cover of Volume 14
Volume 14
by R Greenhalgh (Ed)
Published by Pitman & Sons Ltd
16th April 1927
No ISBN number
Extract from page 652
Flat or Camber Arch
In setting out these arches, the top and bottom edges are equally divided for the voussoirs, as too much room would be required to line out the radials to a centre
The objection to this method is that very acute angles are formed on the voussoirs as they approach the skewback, creating a liability to fracture even under a small load, or through a slight settlement
If we consider the complete arch as a wedge, it is obvious that the flatter the splay of the wedge, the greater will be the friction on its sides. This wedge constructed in soft brick would, therefore, be bound to break across its weakest point before it would settle under a load, on account of the friction at its abutments
Whatever the actual depth of the arch, the angle of skewback is constant, and the arch should always be set out as being 12" in depth. The method of setting out a camber arch, either 9" or 18" high, is shown in Fig. 59
If these arches are set with the soffit perfectly level, they appear to sag in the centre. To overcome this illusion, they are given ⅛" rise to every foot in span
In setting out these arches, the top and bottom edges are equally divided for the voussoirs, as too much room would be required to line out the radials to a centre
Flat or Camber arch
Fig. 57 - Volume 14 page 651
One of the older methods, used for constructing these arches, was to build them up on an inverted equilateral triangle, the base of which represented the springing line, and the sides of the triangle forming the skewbackFig. 57 - Volume 14 page 651
The objection to this method is that very acute angles are formed on the voussoirs as they approach the skewback, creating a liability to fracture even under a small load, or through a slight settlement
If we consider the complete arch as a wedge, it is obvious that the flatter the splay of the wedge, the greater will be the friction on its sides. This wedge constructed in soft brick would, therefore, be bound to break across its weakest point before it would settle under a load, on account of the friction at its abutments
Flat or Camber arch
Fig. 59 - Volume 14 page 652
This type of arch at its best is weak, and will not carry any great load. To overcome this liability to fracture, these arches are now constructed with a skewback, obtained by the following rule: Allow 1" skewback for every foot in span, the depth of the arch on the face to be 12"Fig. 59 - Volume 14 page 652
Whatever the actual depth of the arch, the angle of skewback is constant, and the arch should always be set out as being 12" in depth. The method of setting out a camber arch, either 9" or 18" high, is shown in Fig. 59
If these arches are set with the soffit perfectly level, they appear to sag in the centre. To overcome this illusion, they are given ⅛" rise to every foot in span
ReplyDeleteGood stuff . Easy to understand . A bit of detail on how to make the template for each brick , would be helpful .
Thanks
Mark.