Revision of the Niagara Railway Arch Bridge . oints for secondary stress were located nearthe main top gussets and in large enough numbers to obtain results * Transactions, Am. Soc. C. E., Vol. LXXXII (1918), p. 1040. 1948 REVISION OF NIAGARA RAILWAY ARCH BRIDGE for both longitudinal and transverse secondary stresses. Points werelocated on Post U2 L2 at two elevations below the highway deck, and,for the arched chord, they were located inside the chord members. Thelocation of the temporary and permanent gauge points was recordedin tabular form. Spots about 1£ in. in diameter were cleaned of pai
Revision of the Niagara Railway Arch Bridge . oints for secondary stress were located nearthe main top gussets and in large enough numbers to obtain results * Transactions, Am. Soc. C. E., Vol. LXXXII (1918), p. 1040. 1948 REVISION OF NIAGARA RAILWAY ARCH BRIDGE for both longitudinal and transverse secondary stresses. Points werelocated on Post U2 L2 at two elevations below the highway deck, and,for the arched chord, they were located inside the chord members. Thelocation of the temporary and permanent gauge points was recordedin tabular form. Spots about 1£ in. in diameter were cleaned of paint and rust andplaced either 8 in. or 20 in. apart as needed. The holes for theu points were drilled with a Yankee drill about -^ in. deep, andwith a No. 56 drill. The burr was removed by a flat-angle countersinkand finished by rubbing with a center punch. One hole of each pairwas finished before the other was marked, by using a bar with centerpunches spaced 8 in. apart. The holes were protected when not inuse by filling them with Heavy Lines indicate members on whichstress measurements were made. Fig. 11.—Members of Niagara Arch to Which Strain Gauges Were Applied. Permanent Gauge Points.—These were placed on members, as indi-cated in a list in the Company files, so that readings on such memberscould be checked up for different loadings at any future time. Thesepoints were set in the bottom of £-in. holes I in. deep, which weretapped and provided with cap-screws having a lead washer under theheads. The holes were filled with vaseline before the cap-screws wereput in place. Modulus of Elasticity.—The modulus of the steel in the bridge isthe basis on which the strain-gauge readings have been reduced, andthis is undoubtedly 29 000 000 lb. per sq. in. The character of thematerial was specified to be steel having a strength of from 60 000 to REVISION OF NIAGARA RAILWAY ARCH BRIDGE 1949 68 000 lb. per sq. in. and an elastic limit of at least 33 000 lb. per sq. in.
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