Chap. XXIII.
1371
Bridge of three Arches over the Loire , each 92 feet span, with a clear width of car-riage-way of 27 feet, and a versed sine of 8 feet 6 inches; they are well framed
Fig. 2239.
BRIDGE OVER THE LOIRE.
together; nine pendantbinding pieces radi-ating to a centre main-tain the polygonal tim-bers that form the archin their position; andwhere these pendanttimbers increase inlength towards theabutments, they areagain strutted securely.
Over another arm ofthe Necker is a horsebridge 90 feet span, anda clear width of way of10 feet, in which thependant pieces are theposts that form theparapet.
The king-posts inthis bridge are placedperfectly perpendicular,and the side braces ap-
Fig. 2242.
BRIDGE OP VRACH IN WURTEMBERG, OVER AN ARM OF THE NECKER.
Fig. 2240.
Fig. 2241.
LOIRE.
plied to their sides spread to the full extent of the opening, having their abutments againsteach other on the piers : a nail is introduced between the tops of the several king-posts,which serves as a straining piece, and prevents them from approaching each other. Thefloor is carried in the middle of the span upon a stout transverse bearer, suspended to theends of the king-posts by means of iron straps and bolts. So long as decay is prevented, andmain timbers preserve their form, this construction is durable and economical; but if theheads of the piers are suffered to break the tie by which they are held in their perpendi-