The Civil engineer and architect's journal, scientific and railway gazette . they were built of any material at present known, because atthe points of rupture, the resultant pressures act at the extremeedge of the voussoirs, and therefore all the pressure has to be re-sisted by these extreme edges, or by a single line, which cannot bethe case, unless the material is incompressible. So that in allpractical cases of arches, even the condition of unstable equili-brium cannot be attained, unless the position of the line of resist-ance is some distance within the section of the arch. The ques-tion
The Civil engineer and architect's journal, scientific and railway gazette . they were built of any material at present known, because atthe points of rupture, the resultant pressures act at the extremeedge of the voussoirs, and therefore all the pressure has to be re-sisted by these extreme edges, or by a single line, which cannot bethe case, unless the material is incompressible. So that in allpractical cases of arches, even the condition of unstable equili-brium cannot be attained, unless the position of the line of resist-ance is some distance within the section of the arch. The ques-tion which then arises is, how near to the intrados or extrados canthe line of resistance pass, without causing the failure of the ma-terials . Art. 13.—Experiments to determine the strength of stones toresist compression, have for the most part been made by the ap-plication of pressures on cubes of the stone, in a direction perpen-dicular to the face of the cube, as in diagram 10. The resultantof this pressure, and the weight of the stone, acts in the direction Diagram Diagram 11. of the axis of the cube. Its point of application being in the centreof the base at p ; so that if any line be drawn through this point p, tothe edges of the block, as the line A B, the portion p A\% equalto the portion p B : and as, by the principle of the equality ofmoments, the pressure on the point A, multiplied by the lengthAp, is equal to the pressure on the point B, multijdied by thelength Bp; since the length Ap, is equal to the length B p, thepressure on the point A, is equal the pressure on the point B; andsimilarly the pressure on the w hole edge of the stone e h, is equalto the pressure on the opposite edge/g. Now let the block of stone, as shown in diagram 11, be actedupon by a pressure whose direction is inclined to the axis of theblock, but which is applied in such a position, that the resultantof it, and the weight of the block, acts through the point p, inthe centre of the base. Dr
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