Bridge building

“ This noble work of art, which is unequalled in the history of bridge-building, crosses the Dee at the south-east angle of the Roodeye, and is approached by a new road from the centre of Bridge-street, which passes by the Castle esplanade, proceeds across the City Walls, and then, by an immense embankment, thrown over a deep valley, to the foot of the bridge. The bridge consists of one main stone arch, with a small dry arch or towing path on each side, by which the land communication is preserved on both sides of the river. The cost of erection was £36,000. ”

“ But the main point is that the archways made by Nature not only suggested the arched bridge of handicraft, but heralded all the lovely styles of building which have used vaults, domes, turrets, towers, spires, steeples, and arched openings—gateways, porches, and windows. There is a rival art, as we know, an art which has glorified the long lintel-stone carried by pillars; but it has never won from the genius of great men the highest technical inspiration. ”

“ With the advent of the era of railway building, and as the number of the shining rails increase yearly at these geographical centers, the strategic nature of the portage routes has been and is still being strongly emphasized. Engineering art is now defying nature everywhere, and daring feats of bridge-building are daily accomplished ”

“ It is no use my reminding you that no railroad goes to the old home place. It isn't there any more, even in outward seeming. Cummins's woods, where you had your robbers' cave, is all cleared off and cut up into building lots. The cool and echoing covered bridge, plastered with notices of dead and forgotten Strawberry Festivals and Public Vendues, has long ago been torn down to be replaced by a smart, red iron bridge. The Volunteer Firemen's Engine-house, whose brick wall used to flutter with the gay rags of circus-bills, is gone as if it never were at all. ”

“ To-day a new era in bridge-building is heralded by rapid improvements in airships and aeroplanes; there should be a congress of architects and engineers to discuss the urgent questions of national defence that the piers and footways of bridges bring before our common sense, 335, 358. ”

“ It has a span of 200 feet, with a rise of 42 feet. An arch, however, in the Washington Aqueduct extends to 220 feet span, while the central span in the Southwark Bridge, designed by Rennie, is 240 feet. This last, however, is of cast-iron.
The principle of the arch, however, does not appear first in the history of bridge building. Bridges are as old as mankind; that is, no one knows when first men began to cross streams and chasms by placing the trunk of a tree from one side to the other, and thus bridging the gulf. ”

“ THE ARLINGTON MEMORIAL BRIDGE DEVELOPMENT, LOOKING TOWARDS THE LINCOLN MEMORIAL
[142]
At the center of the bridge is a drawspan, each leaf of which has a length of 92 feet, the height of an 8-story building. One minute is required for opening and closing the drawspan, which is operated by electricity. Each leaf weighs 6,000 tons. It is in itself an interesting achievement in bridge engineering. ”

“ Bridge building is a serious business, and I would not advise any one to attempt building this, of all bridges, who does not propose to follow instructions implicitly. Uncle Ed told us that if we built it properly, and with sound timbers, we would find the bridge strong enough to support a dozen boys, but he warned us not to crowd more than that number on it.
Frames for the Cantilever Bridge.
Fig. 305. A Frame (make four) .
The frames with which the cantilever bridge was built were made of saplings from 3 to 4 inches in diameter. We procured them from Mr. Schreiner’s lands up the river. ”

“ We have to build great masses of stonework, and imbed in the masonry enormous steel bars linked together like giant chains, to which the cables are fastened. The anchorages of this bridge are each as long as a city block (225 feet) , and 175 feet wide, and when they are finished, they will be built up as high as an eight-story building.”
With this impressive introduction, Mr. Blanchard led the way up to the anchorage, and let us see for ourselves the huge chain of eye-bars. They were stringing the cables in separate strands, and each strand was fastened to a separate pair of eye-bars. ”

“ The simplest bridge that can be built, is a single beam, or stick of timber, spanning the opening between the abutments—but this is only of very limited application— (only for spans of 20 feet and less) owing to the rapid increase in sectional dimensions which is required as the span becomes greater. ”

“ This bridge and its approaches cost eighty millions of dollars, and is used by ten or twelve railroad companies. Above the tracks is a big street with carriage-roads, street-cars, and walks for foot-passengers.
The honor of building the finest bridge in the [31] world would have satisfied most men, but not ambitious Captain Eads. ”

“ But it is not to be looked upon as the only suspension bridge along which our arboreal ancestry capered, and from which primitive mankind took, and take, hints in bridge-building. Let us remember also the pendent bridge of lianes, and of other tough creeping plants, which in many warm countries grew, and grow, from tree to tree, forming strong cables. On such a high-swung bridge I can see the Dryopithecus, suspended by his [Pg 115] hands, and learning tricks as a gymnast, while his mate squats between the fork of a branch and collects fleas from her baby. ”

“ The same ingenious propensity to shorten their labour, seems to have given birth to a contrivance still more extraordinary: this is a kind of bridge, or vast arch, sprung from the floor of the area to the upper apartments at the side of the building, which answers the purpose of a flight of stairs, and must shorten the distance exceedingly in transporting eggs from the royal chambers to the upper nurseries, which in some hills would be four or five feet in the straightest line, and much more if carried through all the winding passages which lead through the inner chambers and apartments. ”

“ In this situation a bridge of ninety-five feet, or equal to the extreme breadth of Princes Street, would most unfortunately place the new buildings upon the north-western side so near to the houses of Leith Street, that the windows of the houses of Leith Street and those of the new street would be shaded by each other, so as to require the buildings at the western end of the bridge to be kept less in height, if not to be discontinued altogether, for a considerable way, which would render the building grounds of much less value. ”

“ He states that he has felt with his measuring rods the timber, &c., placed in the river to strengthen the piers of the Great Arch, and that his sounding leads have been broken by catching in it. In April, 1826, the opening of the roadway of London Bridge for throwing of two more Arches into one, to increase the water-way during the building of the New Bridge, also made a curious discovery of many of the more ancient parts of the original building. ”

“ In the construction of the new bridge it became necessary to dismantle the draw of the old one, and to erect temporary supports while the timbers and draw of the new bridge were being put in place. To prevent the stoppage of its trains while this building was going on, the company constructed a temporary bridge adjoining the old one, for their transportation; expecting to have the new bridge completed before the winter rise, which usually began near the close of December, should render the river navigable. ”

“ II To be brief, it is evident that the bridge-building of modern times—from the Renaissance to our own day—has been nothing more than a long series of experiments from which a good many important matters have been excluded. High artistic qualities were divorced from military forethought by the earlier pontists of the Renaissance ”

“ The useful and necessary thing is to visualise the fact that varied hints on bridge-building accompanied the descent of man, so the influence of their utility was active through all the linked growth in that organic chain by which the earliest men and their nearest allies were united. ”

“ Everywhere defenceless bridges have been the cause of much anxiety, and dozens have been destroyed because they could not be turned into rearguard defences. Wellington said that his sappers in five minutes could blow up a modern bridge. In the present campaign sappers have done this work under fire, mining strategic highways being a simple job. How ludicrously tragic is the contrast between the building of a modern bridge and its easy demolition! ”

“ The stones used in the building of this structure were so strongly cemented with different kinds of mortar, and strong iron clamps, that the workmen found a most difficult task in the demolition of it, which is not yet completed.’ The Committee for altering London Bridge had, however, previously advertised for persons to carry their intentions into effect, to meet at Guildhall on the 1st of February, 1757 ”

“ The verticals are of wood, and the diagonals foot on steps formed by enlarging the ends of the verticals. The counters are in two lengths, and are adjusted by wedges at the points where they intersect the braces. The bridge is in two spans, and has a double track, and consequently three trusses. There are two timber arches to each truss, and the truss is supported on them by connecting them to the verticals by short cross pieces notched into the posts, and resting on the upper surface of the arches. ”

“ In the upper of these prospects, the Northern end of London Bridge is shewn to be a passage fenced by wooden palings without any houses, excepting one building, which occupies the whole width of the Bridge; having a gate in it surmounted by the King’s Arms, and standing immediately before the old Church of St. Magnus. ”

“ The general dimensions of the transverse floor beams, when about 3 feet apart, from centre to centre, are 8" x 14", the largest dimension being the depth. The stringers should be notched to the floor beams about 1" or 2", and should be about 10" or 12" x 14". The cross ties should be 18" to 24" apart, from centre to centre, and be 31⁄2" x 6".
Large, heavy bridges require no fastening to connect them with their seats, but light bridges should be fastened, as the spring on the sudden removal of a load, (as when the last car of a train has passed,) may move it from its proper position. ”

“ But now, to obtain the dimensions of the web members, so called, of the Truss, it is necessary to decide upon the specific variety. The form of Bridge in more general use in the United States is called the Howe Truss, from its inventor, and in spans of 150 feet, and under, is very reliable; for spans exceeding 150 ft. it should be strengthened either by Arch Braces or by the addition of Arches, as the heavy strains from the weight of bridge and load bearing on the feet of the braces near the abutments, tend to cripple and distort the truss by sagging, although the Baltimore Bridge Co. ”

“ We may believe, however, from all the circumstances attendant upon the fire, that the stone-work of the Bridge was so battered and weakened, ‘that it cost the Bridge-House £1500. to make good the damage in the piers and arches, before the leaseholders could attempt to rebuild the premises destroyed by the fire.’ Though ‘the stone work,’ continues this passage, ‘was no sooner secured, than a sufficient number of tenants offered; who conditioned with the Bridge-House for building-leases of 61 years, at the rate of 10s. ”

“ To enable the contractors to make an early start with the permanent work, that is, the building of the masonry piers, it was necessary that the positions of these should be fixed without delay. A base line about 4000 ft. in length was laid down along the high ground on the south shore, starting from a point in the centre line of the bridge, passing along the North British Railway for some distance and terminating opposite the east breakwater at Port Edgar. Along the breakwater a timber gangway was erected, and near the far end of it, at a distance of about 3000 ft. ”

“ Emiland Gauthey’s “Traité de la Construction des Ponts,” 127; Colonel Emy’s “Traité de l’Art de la Charpenterie,” 143 footnote; Professor Fleeming Jenkin’s “Bridges,” see “Jenkin”; E. Degrand’s “Ponts en Maçonnerie,” 88. Booths or Shops on Chinese bridges, 210 footnote; [Pg 380] on European bridges, 210. Bordeaux, Pont de, its length and its cost, 356. Boughs, Forked, in primitive bridge-building, 135, 148. Bower Birds, Australian, their architecture is a model to all primitive men, 112.
Brackets, below the parapet of the Pont Neuf at Paris, 321. ”

“ So the design is a clever feat not merely of repetitive decoration, but of repeating solids and voids that oppose each other in a harmony of contrasts; for the empty spandrils in their form oppose the leaf-shaped openings made by the arches, and all the curved solids of the bridge are foiled in a rugged manner by the upright columns, as well as by the long horizontal lines of the covered roadway. In the contrast between cold granite and warm brick there is colour also, and it suits the pulsating light and heat of Italy. ”

“ It is a matter of notoriety that railroad bridges are built upon solid abutments of mason-work and resting on piers of stone between the abutments, thus giving strength and security to the frame above. It is not easy to see wherein such a structure differs from an ordinary bridge, except that, as it is to endure a greater burden, it is more solid and substantial. ”

“ Instead of the arched roof and masonry side-walks of the ordinary underground, there is a rectangular structure with a framework of steel beams riveted together, concrete enclosing the erection completely at the top and sides, and forming the bottom, rows of steel columns helping to support the roof between the tracks—in other words, a kind of Britannia Bridge let into the surface of the earth. ”