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Fortunately, the bridge had suffered no damage as yet, and no one foresaw the effect which these altered conditions were to have. The actual erection of steelwork was impossible during the coldest months; Parker had planned only to rush the piers, abutments, and false-work to completion so that he could take advantage of the mild spring weather preceding the break-up.
The central span of the viaduct is an arch of 220 ft. span between abutments, and about 90 ft. height; the remainder of the space on each side is divided into two spans by an iron pier at a distance of 68 ft. from the retaining wall. These piers are 36 ft. 2 in. high, and carry girders 144 ft. long, balanced each on a pivot in the center.
No attempt was made to water-proof these abutments, but, in the rear of the wall, open spaces were left, about 6 ft. from center to center, which were connected with drain pipes at the base of and extending through the wall, for the purpose of carrying off any water that might develop in the rock.
Hence it early occurred to George Stephenson, when constructing the Liverpool and Manchester Railway, to adopt the simple cast-iron beam for the crossing of several roads and canals along that line—this beam resembling in some measure the lintel of the early temples—the pressure on the abutments being purely vertical.
The rest of that day was spent in planting two stout posts, one on each side of the river, close to the old bridge abutments, and in stretching across the river, from one post to the other, a wire cable that Mr. Elmer had bought for this purpose.
An arch consists of a series of wedge shaped blocks, known as voussoirs, arranged in a curve, and so locking one another together that unless the abutments from which the arch springs give way, it will not only carry itself, but sustain a heavy load.
Presently appeared the heavy walls inclosing the City itself, dominated by the tall openwork timber spire of Saint Paul's, with the four-square, four-turreted Tower acting, as it has been well said, as a padlock to a chain, and the river's breadth spanned by London bridge, a very street of houses built on the abutments.
Each box was washed out at frequent intervals, and there was no clogging of the drains whatever. This method of keeping the drains open was adopted and used successfully for the entire work. The abutments were built of concrete, and the mixture was 1 part of cement, 3 parts of sand, and 6 parts of broken stone. The concrete was mixed in a No. 3 Ransome mixer, and was placed very wet.
He goeth forward and commendeth himself to God, and cometh in the midst thereof and seeth that the bridge was the fairest and richest and strongest he had ever beheld, and the abutments thereof were all full of images.
Now all that remained to tell of this former prosperity were a few rotten piles in the river where the wharves had stood, the bridge abutments, a handful of tumble-down houses, and here and there in the dense woods traces of cultivated fields, and an occasional brick chimney or pile of stone to mark the site of some old plantation house. Mr.
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