Ch_ap. XXIII.
1S77
Bridge of Mellingen, constructed by Ritter, a carpenter of Lucerne , in the year 1794, has anarch of 157 feet span. The two principal timber arches are arcs, equal to the sixteenth ofthe entire circumference of the circle of which they are portions j they are formed
Fig. 2265.
BRIDGE OF MELLl.NGEN.
of six pieces of fir, each 10 inches square : twelve vertical binding-pieces are suspended
to them, extending from the plate that carries the roof to the longitudinal timbers whichsupport the platform or roadway of the bridge, and down to another timber arch, of a flattersegment than those already described, formed of single timbers, and, though apparentlyintended to assist in supporting the roadway, adds very little to its strength, but materiallyto its weight.
Bridge of Tournous , constructed over the Saone in the year 1801, has five equal arches of 89feet span, carried on stone piers, 16 feet 6 inches in thickness : they are arcs of circles, one-sixth of the circumference, and each is formed of six ribs composed of three pieces of benttimber, 9 inches in height, and 11 inches in width; the ribs are 4 feet 8 inches fromcentre to centre; twelve radiating pendant binding-pieces, about 6 feet 6 inches apart,support the longitudinal timbers that carry the platform or road ; in the intervals betweenthese is an iron bolt, which passes through the three thicknesses of bent timbers, screwsthem firmly together, and prevents their springing.
Bridge over the Seine, in Paris * erected in the year 1802, has two arches, each 104 feetspan, with a versed sine of 6 feet 6 inches: the two main arches consist of four
i ii inf
Fig. 2266.
BRIDGE OVER TUB SEINE.
thicknesses of timber, 10 inches
Imirfril
niUiilli 8 ii HUlti T11'
liiiilJlil
ia2 ai
square, bolted together with great ^
v. , tuci«; ai c uv niktri iiicuidtc J.11 iw
cipals, although the bridge is 32 feet
wide. An arch is thrown acrossthe space between them, continuing
the whole length of the bridge, andabutting against the two principallongitudinal arches, which areprevented from yielding to thethrust by a number of iron tiesabove and below the arch, and I 1crossing from one side of the bridge j— A —
to the other. J_ 'J-
The Timber Bridge at Grenelle was p == f =an excellent specimen of an arch ofbent timbers supporting the plat- •form: there was another of this kind T
constructed over the Seine at Ivry, I — Tin 1828, by M. Emmery, who pub- '—<
lished a description of it a few years Fig. 2267. timber bridge at grenelle.
4 T