Annual report of the City Engineer . City Engineer. When the southerly half of the old bridge was stripped inOctober, 1907, preparatory to the erection of the street rail-way structure, the old metalwork was cleaned of scale andrust and its condition was found to be much worse than hadbeen expected from an examination made in the summer of1906, and showed in a striking way that the usual examina-tion of such a bridge from below is by no means real inspec-tion and cannot be relied upon to determine the true conditionof a bridge in which corrosion is well under way. Theworst effects of corrosion
Annual report of the City Engineer . City Engineer. When the southerly half of the old bridge was stripped inOctober, 1907, preparatory to the erection of the street rail-way structure, the old metalwork was cleaned of scale andrust and its condition was found to be much worse than hadbeen expected from an examination made in the summer of1906, and showed in a striking way that the usual examina-tion of such a bridge from below is by no means real inspec-tion and cannot be relied upon to determine the true conditionof a bridge in which corrosion is well under way. Theworst effects of corrosion were generally found at the easterlyend of the bridge over and near track No. 1, which is theoutward bound express track of the Boston & Albany Rail-road. This track is also used by switch engines in makingup trains in the railroad yard just east of the bridge. Thetotal train movements beneath the structure is between fivehundred and six hundred on each week day, and abouteighty on Sunday; and frequently the switch engines will. FIG, STREET BRIDGE. TYPICAL CORRODED DIAGONAL OFORIGINAL TRUSSES. Engineering Department. 47 stop underneath the bridge, discharging steam and smokewhich hang for a considerable time just under the bridgefloor. The floor beams at the east end of the bridge werethe parts found to be in the most dangerous built before the days of modern street cars anddesigned only for a uniform load of eighty pounds per squarefoot and a single twenty-ton wagon, these floor beams werecalled upon to support two car tracks, each carrying carsup to twenty-six tons in weight, in addition to the usual andfrequent highway traffic at each side of the roadway. If thesewrought-iron beams had been as good as new they wouldhave been subjected, under this loading, to unit stresses ofabout 15,000 to 16,000 pounds per square inch in was found, however, that the beams in the worst conditionhad corroded to such an extent that their webs, origina
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