CHAr. XXV.
ON STONE BRIDGES.
1499
Fig. 2738. Fig. 2739.
abutments were 24 feet, and the weight was increased upon the arch, they each slid uponthe platform, as shown in fig. 2739., and the three voussoirs altered their position.
Fig. 2740. shows one similar abutment to the last, and the other replaced by one 36 feetthick, formed by three stones; on striking the centre, the abutments, which was of one
Fig. 2740. Fig. 2741.
stone, did not move; the upper portion of the other slided horizontally, whilst the lowerremained stable, as in fig. 2741.
Fig. 2742., one abutment being substituted, 32 feet thick, of a single piece; the secondof the same thickness, composed of four pieces, three of which were cut, with joints radiating
Fig. 2742.
Fig. 2743.
to the centre of the arch: the abutments resisted until one-seventh of the weight of thearch was added, when it assumed the form shown in fig. 2743.
Fig. 2744. shows one abutment of a single stone, 36 feet thick, and others of 65 feet, com-posed of four pieces : when the centre was struck, the key sunk, and the joints opened at
Fig. 2744. Fig. 2745.
the intrados, and it remained in this position; but a trifling weight added gave it thecharacter shown in fig. 2745.
Fig. 2746., two abutments of 36 feet, one divided into five pieces : in this case the archsupported one-fifth of its weight; it then gave way, as seen in fig. 2747. : if a resistance be
placed beyond the abutment, composed of severalpieces, the arch will support more than three-fourths of its weight without yielding, as seen infig. 2748.
Fig. 2749., with two arches and one pier, thefirst abutmentformed of fivepieces, 36 feet inthickness, and theother six pieces,and 72 feet thick:on adding a slightweight to thearches, theupper part ofthe latter slipt,and the otherresisted, as infig. 2750.
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1 . . ■ V
r
Fig. 2748.
Fig. 2749
1
Fig. 2750.