|The cement age
|Vol. 11 No. 6
An interesting test of special reinforced concrete has been conducted by the Grand Trunk Railway Company at Mimico, Ont. The Company recently built a concrete roundhouse, a brief reference to which appeared in Cement Age some months ago. Concerning the test the Engineering Record gives the following interesting facts:
"The object was to inform definitely the officials of the railway the exact strength of the roundhouse under construction. For this reason the panel was made as nearly as possible like one of those in the roundhouse. This section was rectangular, supported on four columns, one at each corner. These columns are 26 ft. 2in. on centers one way and 9 ft. the other way. The entire top was covered by a slab 4½ in. think, supported by girders, and a shallow beam connected the columns across the 10-ft. direction. The reinforcement of the slab, however, extended only between the long beams, the latter carrying the load completely. The girders were 14 in. wide and 20 in. deep below the slab, reinforced each with two 1¼×3¾ in. trussed bars running the full lengthy, and one 1x3 in. trussed bar 10 ft. long, which was bent up at the ends. These bars contained diagonals 24 in. length and 12 in. on centers. The slab was reinforced with ½×1½ in. trussed bars spaced 16 in. on centers. All reinforcing metal was at least 1 in distant from the outer edge of the concrete. The four columns were each 14 in . square and 11 ft. high, and were reinforced with ½×1½ in. trussed bars, one at each corner with diagonals pointing toward the center. The concrete was composed of National Portland cement, bank sand and bank gravel, mixed in the proportions of 1:2:4.
"The structure, as outlined above, was allowed to remain for several months, during the construction of the roundhouse. On July 26 it was tested. A bottomless plank box was built on the entire restructure and filled with gravel until the ultimate strength of the structure was reached."
It was deemed unsafe to impose additional weight after the load had reached 1260 lb. per square foot, when there was a deflection of 4 inches in the beams and 6 inches in the slab.
The Record comments as follows upon the result of the test:
"It may be pointed out that this structure was an isolated panel, and therefore could not be considered as strong as if it were incorporated in an extensive structure, such as the roundhouse. This probably caused great eccentricity in the columns when the beams reached their ultimate loading, and therefore the test should not be considered with reference to the columns. The evidence shows, however, that in columns reinforcement, as well as in beams and girders, it is desirable that whatever sheer or diagonal members are used should be rigidly attached to the main tension member. Unless these two parts are rigidly connected there can be little resistance offered by them to the bending of the column or beam."
Ref: Mimico Yard