The Civil engineer and architect's journal, scientific and railway gazette . of rupture will be at the crown of the arch : this isnearly self-evident, and may be proved by experiments on anymodel of an arch ; it is, however, proved geometrically by applica-tion of the problem in Section 4. If the arch fails at the crown,by the voussoirs turning on their edges A,, at the extrados, as indiagram 7, then at some point in the haunches, the voussoirs willat the same time be turning on their edges A,,, at the intrados, inwhich case the crown will sink and the haunches will spread. If the arch fails a
The Civil engineer and architect's journal, scientific and railway gazette . of rupture will be at the crown of the arch : this isnearly self-evident, and may be proved by experiments on anymodel of an arch ; it is, however, proved geometrically by applica-tion of the problem in Section 4. If the arch fails at the crown,by the voussoirs turning on their edges A,, at the extrados, as indiagram 7, then at some point in the haunches, the voussoirs willat the same time be turning on their edges A,,, at the intrados, inwhich case the crown will sink and the haunches will spread. If the arch fails at the crown, by the voussoirs turning on their•dges at the intrados, as in diagram 8, then at simie point in thenaunches, the voussoirs will, at the same time, be turning on theiredges Aj, at the extrados, in which case the haunches will sinkand the crown of the arch will rise. Art. 8.—When the arch is failing, as shown in diagrams 7 and 8,then the points of application of the resultant pressures at theplaces of failure are beyond the edge of the voussoir, as shown in. sultant pressure must be at the extreme edge of the voussoir, andits direction must also be that of the tangent to the intrados, orextrados, at A,, Aj, &c., because if not, the line of resistancepasses without the boundary of the voussoirs, either on one orotlier side of the point A, and tlie structure has already failed, bythe turning over of some other voussoir. Therefore, wlien thearch is in the condition of unstable equilibrium, then, at all thepoints of rupture, the directions of the resultant pressures are tan-gents to the intrados, or extrados. Art. 9. Pruhlem 2.—To find the second point of rupture, in anarch whose voussoirs are incompressible, the form of whicli and thepressure sustained by it, as regards position, direction, and amount,being similar on either side of the crown of the arch. Also to find the amount of pressure at the crown and at thesecond point of rupture. Take for example an arch w
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