Chap. XXIII.
1373
polygon was given to the several struts and supports : regarding each side of the polygonthat abutted on the piers as a simple truss, and proportioning the timbers to theduty they had to perform, there perhaps could not be a more simple arrangement, orone that offered, with the same amount of material, greater strength ; but the quantity offramed work and the liability to cecay in the several joints have occasioned this system tobe abandoned.
Bridge of St. Clement , over the Durance , with a span of 115 feet, was an early instance ofthe application of the suspension principle. The length was divided into nearly three equalparts; in the middledivision an addition-al timber was placedunder the main lon-gitudinal beam, towhich it was firmlybolted, and the di-vision was held upby four radiatingposts, which werekept in their positionby strong straining Fig -2251. bridge of st. clement.
pieces introduced between their heads, and by a St. Andrew’s cross framed in between them;the centre framing formed almost a single mass, and was kept from sinking by diagonalstruts resting on the abutments ; the lower of the two, from their inclination being so flat,could not be very effective, and the principal stress in consequence must have been thrownupon the others, which abutted against the top of the suspendant posts; these diagonalstruts had also two pendant binding-pieces and cross struts, to assist in carrying theplatform of the bridge, and prevent their springing. After the timbers had shrunk,the whole weight of the bridge must have been thrown upon the upper pair of struts,which abut against the pendant binding-pieces.
Bridge at Savines has a clear width of way of 10 feet, and a span of 75 feet; it is alsoupou the suspension principle, but the timbers are more simply arranged ; the abutments
Fig. 2252.
BRIDGE AT S<Y' INES.
are of timber. In the centre is a post 16 feet in height above the platform of the bridge,into the head of which are framed two diagonal struts or principals, one on eachside, for the purpose of suspending it; this post is struttedto the principals, and holds up the middle of the longi-tudinal timbers of the bridges, as a king-post sustains thetie-beam of a roof; other pendant pieces are attached tothe inclined principals, and shorten the bearing, by holdingup the longitudinal timbers at regular distances: all thosebridges formed of braces diversely inclined are defective instrength, and consequently in duration.
Bridge of Schajfhausen was constructed in the year1757, by John Ulrich Grubenmann, a village carpenterof Tuffen. It was formed of two arches, one spanning172 feet, the other 193 feet: this bridge, so cele-brated for its beautiful carpentry, was destroyed by theFrench troops in the year 1799. The abutments as well asthe middle pier were of stone ; the longitudinal timbers orplates were formed by uniting two strong pieces together,en cremaiUere , which were supported underneath by four
inclined struts on each side: above the platform six other inclined struts on eachside supported another longitudinal series of beams; double binding pieces hangingperpendicularly from the upper longitudinal beams, under the eaves of the roof, heldthese struts in their proper position, and prevented their springing. The transverse
Fig. 2253. savines.