1380
THEORY AND PRACTICE OF ENGINEERING.
Book II.
to unite closely and firmly together ; the carpentrywas well executed, all the mortises and tenons cutwith great precision, and the whole protected fromthe weather by a light timber roof.
Bridge at Seurre, on the Saone , is supported uponthe ancient stone piers: the arches are 95 feet span,and are formed of five principal ribs, placed 4 feet9 inches from centre to centre, each composed ofthree pieces, bent one over the other, each piecebeing about 10 inches in width and 16 inches deep ;the versed sine is 11 feet 6 inches. The timberswhich carry the floor are 12 inches by 10, andare supported by inclined pieces, which are not ofmuch utility : the eight pendant binding-pieces areformed out of timbers 9 inches square, and iron boltsand straps are frequently introduced to add to itsstrength.
The Bridge at Choisy has five arches supported onstone piers and abutments, the span of winch is 67 feet, and their versed sine 8 feet9 inches: each of the three timbers which form them is 10 inches in width and 12inches in height; pendant binding-pieces with iron bolts are introduced in the intervals,to secure the bent timbers. The longitudinal timbers that carry the parapets and platformhave a double thickness over the piers ; on these lie the transverse timbers that supportthe planking of the floor, which is formed of two thicknesses : this bridge was completedin the year 1811.
M. Ifiebeking, director-general of the bridges and roads in Bavaria , has published manydesigns of bridges executed under his direction since the year 1807. and by him the con-struction with curved ribs has been greatly improved : instead of using short pieces of tim-ber he employs those of considerable length,and bends them one over the other to suitthe curve required ; the number of joints islessened as much as possible, which rendersthe ribs stronger, and less liable to decay.
The Bridge of Xeucettringen , over the Inn,was one of M. 'Wiebeking’s first workswhere curved ribs were used : it is com-posed of five arches with stone abutments,the span of which are 102 feet 6 inches,and the versed sine about of theirspan. The breadth of the bridge is 24 feet6 inches, and there are but two principals toeach arch, each formed of three courses oftimbers, one over the other ; the courses are13 inches in height and width: five trans-verse girders rest on the curved ribs, andoccupy the depth between their topand the horizontal timbers that support thefloor ; those in the spandrills have an extradepth : between the transverse girders, which F ’g. 2276. brjdge of neccettringf.n.cross the principal ribs, are struts laid hori-zontally, and the whole is pinned securely and bolted with iron : into the projectingends of the transverse girders are framed upright posts, which are strutted and form theparapets.
In the spandrills, or the space between the curved ribs and the longitudinal timberswhich carry the floor, are vertical timbers, called piers of tension; from these issue struts,which are more or less inclined as they are placed farther from the abutments. The abut-ments of the arches are 10 feet within the face of the masonry ; the piers consist of arow of nine piles, the ones inclined, to give the greater stability. Starlings are formedabove bridge: all the timbers were well pitched, and the whole was covered with planksexternally, which are removed in the fig., to show the construction.
Freysingen Bridge , over the Isar, in Bavaria , was constructed by M. M’iebeking in theyear 1808, and consisted of two arches, 152 feet span, with a rise of 11 feet 6 inches, theradius of curvature being 246 feet: the width of the bridge is 24 feet 6 inches; therewere three sets of curved ribs in the section transversely; each arch of these sets had threecurved ribs, united at seven points by as many pendant binding-pieces, which supportedseven ranges of beams laid in the direction of the length of the bridge, with diagonal bracesbetween them, the joists that supported the road being laid across them The ribs that
PELDKIRCH.