circular, fig.21, whose thickness is one-ninth of its radius, the line of equalhorizontal thrust just touches the extrados at the crown, andthe intrados at the haunches, pointing out the places wherefailure would take place with a less thickness or an unequalload, by the voussoirs turning on their… … they are well backed up. Pointed arches have a tendency torise at the crown ; and, to prevent this, the cross springersof the ribbed vaults of the middle ages were often made of asemicircular profile, their flatness at the crown being con-cealed by the bosses at their intersections. 70. If the…
Architecture · Building
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![An illustration from Rudiments of the art of building : represented in five sections [...] for the use of architects, builders, draghtsmen, machinists, engineers and mechanics (1853)](https://img.insideoutlibrary.com/img/200/ia-rudimentsofartof00bull-51-15.webp)
