Rafael Guastavino

After that we find the line of the extrados of the arch in a graphical manner, derived from the formula given by [Édouard] Dejardin for tracing the equilibrium profile

We use the formula (1) to get the thickness necessary at the centre of the arch

General Formula for Segmental Arches [for distributed load:]\mathrm{TC} = \frac{\mathrm{LS}}{8r} \qquad (1)

[A] brick arch four feet six inches in span, ten per cent... rise, and four inches thick, with cement mortar... [is] equivalent to a ten or twelve foot span in a "Timbrel Arch," three inches thick, and with an eight to ten per cent rise.

is not a safe construction.

15 or 20-foot arches, three inches thick.., with ten per cent, rise... can be laid, taking away the centres and giving them... uses of the building in a few hours, when an arch of brick with a six-foot span, four inches thick and a ten per …

ten days laid... 80 to 150 pounds per square inch, while... our "Timbrel Arch"... test... 287 pounds for ten days

the tension will only equal the cohesive strength of the mortar between the bricks

[S]uppose an arch laid in brick... to receive a test for tension

There are other advantages... [I]n every arch the curve of pressure changes according to the position of the load; this means that every arch must be prepared for work by deflection or tension.

In our arch, in the same six feet (Fig. 14), we have only 13 joints, one-quarter of an inch each.., only three and one-quarter inches of mortar..; the arch with no joints is the best, the one with the least is... preferred.

When this arch rises only ten per cent of the full span it is very dangerous, because the development of the curve measures very little more than its chord C D.

represent about seven inches of mortar

of six-feet span... would have... 26 or 27 joints

[I]f we were able to build an arch without joints, it would be the best, as it would have no settlement; but as the gravity system has only s of stone or brick.., joints are necessary.

[T]his horizontal breaking joint, or new additional strength, is not the only great advantage of the system.

These three remarkable circumstances are of great value to architects, as they can be put in the specifications and can be depended upon as absolute proof of the safety of the .

[T]hird, we can run the centre under the arch again when it is completed, which is the most practical illustration that the arch has has the absolute repose necessary for its settlement.

Second, it is common to see the workmen walking over the arch, free from centres of any kind, some hours after it is built.

First, we can build arches of twenty-feet span only three inches thick, using a centre one inch thick, and moving it along as soon as a row of tiles is laid, which usually requires about fifteen minutes.

[I]n our " Cohesive System," with horizontal broken joints, with 17,820 pounds per square foot shearing strength, the reduction in the vertical joints is prevented absolutely, as can be proved by the following facts...

[I]n the " Gravity System " the mortar serves only as a cushion... because of bad setting, and adds no strength to the arch.

In the "Gravity System" (Fig. 10), the strength of gravity alone is the only force keeping the s in place by pressure against each other in the joints. These joints are not protected, and any reduction in the width of the joints in …

which is a peculiarity of the Timbrel Arch System