Illustration 229 Iron-framing to fireproof flooring (Source: Fairbaim, 1870) Turned through ninety degrees, the end bay arches [form a strong and powerful resisting abutment to the thrust of the transverse arches running from one end of the building to the other'.
(Illustration 228). Some of the floor dead weight may be carried by composite action if the beams are backpropped prior to placement of the concrete. To some extent the brickwork may be self-supporting between the columns by three-dimensional vaulting action. In an arched floor the internal arch bays are mutually supporting. The thrust from the end bays is resisted either by a substantial solid masonry external wall (usually the gable wall), or by wrought iron ties to a cast iron 'thrust beam' built in to the wall. In some buildings, the arches to the end bays are turned through ninety degrees (Illustration 229).
A number of arched floors were patented. From the late 1840s, corrugated wrought iron arch formers were used in a number of building floors (Illustrations 230 and 231). Protected from the weather, the few surviving examples provide a rare opportunity to view riveted corrugated iron in close to its original condition. Gypsum combined with aggregate made 'Nottingham concrete'. This material, with excellent fire resistance, was used in Dennett's patent arch floor (Illustration 232). Dennett's business partner Mr F Ingle described the system as suitable for spans of 6' to 12', the arch thickness at the crown varying from 3" to