It had a simple parapet, formed of a top and bottom rail, supported at intervals by upright posts, with diagonal braces filling in the intermediate spaces. This bridge was unfortu ..
'lately destroyed by the succeeding emperor, to prevent the possible incursions of the barbarians, by its means, into the Homan territory.
The timber-bridge of Schaulfhausen, built over the Rhine, by Ulrich Grubenmann, was remarkable for its ingenious con struction; it consisted of two openings, one 1% feet span, and the other about 190. Its abutments and centre-pier were of stone ; on these were laid a kind of compound beam, formed of three rails or walings, each of which consisted of two longitudinal beams bolted together, and toothed into each other, so as to he perfectly united; these were sup ported by an infinity of struts, kept in their places by vertical binding-pieees, all tending to transfer the thrust to the supports of the bridge. It was roofed in for the ostensible purpose of protecting the timber from the bad effects of the weather ; but there can be little doubt but that the roof added greatly to its strength ; and it is not impro bable that its ingenious architect was aware of the impor taut advantages to be derived from its introduction. This bridge, and others designed and excented by the brothers Grubentnann, were in fact Timber Tubular Bridges.
The beautiful bridge of Schauffhausen was unfortunately demolished by the French, about the year 1800.
delm Grubenmann, assisted by his brother Ulriek, built a splendid bridge of a similar description over the Limmat, having the enormous span of 390 feet. It was formed of two immense circular ribs, one at each side of the roadway, formed of several beams bolted together, and made to fit one into the other, in a similar manner to the Schauffhausen Bridge.
This bridge had also angular struts, longitudinal beams, perpendicular binding-pieces, and abutments of masonry; it was likewise furnished with a roof, which added to the stability of the structure. It was, however, burned down shortly after the destruction of the Schauffhausen Bridge. The bridge at Ceslingen, as also that of Zurich, the one upwards of 200 fret, and the other about 130 feet span, no splendid specimens of this kind of construction, as like wise the bridges of 111 ellingen and Berne, by Bitter, and those over the Saone by Gauthey.
The timber-bridge of St. Clair, built over the Rhone at Lyons, has seventeen openings, the centre one having a span of 45 feet, and the others diminishing towards each bank. This bridge has a roadway of about 36 feet, which is supported upon piers each formed of 13 piles, arranged in a single row, running parallel with the banks of the river ; on the top of these piles a sill was framed, and longitudinal timbers were made to bear over the head of each pile; amid upon these longitudinal timbers the Iloorimr was laid.
The bridge of Grenelle, erected over the Seine, near Paris, by N. Mallet, consists of two equal and symmetrical bridges, separated by an intermediate piece of dry ground ; each of these is fiirined of three timber.bays of 82 feet span, sup ported upon two abutments and two piers of masonry. The width of this bridge is nearly 33 feet. The piers are about II feet wide at their foundations, and are diminished to about 9 feet at the springing. The abutments have a half= pierattached to them, on which the titaber-work rests. Those at the banks of the river have, besides, two wing-walls. The ground in the centre, measuring 85 feet, the whole bridge, reckoning the ( mire distance from the abutments on either bank of the Seine, is 632 feet long.
All the foundations were built on piles, upon which a plank mg laid. These foundations were formed by means of eoller-danis, easily constructed on account of the shallowness of the river, which, at low water, was not more than 5 feet deep ; each bay is composed of seven timber frames, placed about 5 feet apart from each other. The frames consist. of segmental ribs, formed of three pieces of bent timber, hotted and bound together by means of iron, which support the roadway by radiating pendants ; each of these compound seg mental beams is 9 inches square, and of such a length its to take in two of the spaces fimned by the pendants, In elating and placing the frames in position, they were put 5 inches higher than they should have been, in order to allow for sink ing, after the flagging was put upon the bridge ; and even when opened to the public, the bridge had not settled into its place, so it would seem that 2, or at most, 3 inches, would have been amply sufficient to have allowed for.