. Tests of eighteen concrete columns reinforced with cast n spailing of the concrete outside the spiral spread to suchan extent that any further readings of the columns would havebeen unreliable, they were discontinued, and the instrumentsremoved to prevent their being ruined by the falling concrete. (a) Stress Evenly Distributed.—To determine the angular move-ment of the base of the testing machine, and consequently anybending of the column or unequal distribution of compressionstress a sensitive machinists level was placed upon the test-ing machine base and read during the test at the
. Tests of eighteen concrete columns reinforced with cast n spailing of the concrete outside the spiral spread to suchan extent that any further readings of the columns would havebeen unreliable, they were discontinued, and the instrumentsremoved to prevent their being ruined by the falling concrete. (a) Stress Evenly Distributed.—To determine the angular move-ment of the base of the testing machine, and consequently anybending of the column or unequal distribution of compressionstress a sensitive machinists level was placed upon the test-ing machine base and read during the test at the same time asthe compression readings. Since only one level was availablereadings could not be taken in two directions, which would havebeen preferable. The positions of each end of the bubble in thislevel were read, thus enabling the location of the center of the 3 Johnsons formula 34 000—88 -5 gives a reduction of 10 per cent. (Johnsons Materials of Construction.) L 80 000—700 imperfections mentioned above. Bureau of Standards Technologic Paper No. 122. Fig. 6.—Showing column ig ready for testing Reinforced Concrete Columns 17 bubble to be found for each load. The location of the center ofbubble was plotted against applied load for all columns. Thecurves thus obtained were rather irregular and showed no inclina-tion of the platen to move in any definite manner. The largestmaximum deviation showed the base to be turned through anangle of minutes, which is extremely small, or a move-ment of inch in 10 feet. An increase in the angle of devia-tion at the greatest load at which readings were taken mightreasonably have been expected, since the strain ordinate of thestress-strain diagram commences to increase more rapidly at thispoint. No such indication was evidenced, thus showing that anybend in the stress-strain curves was not due to bending or flexureof the columns. (b) Behavior of Columns Under Load.—The method of failureof all columns was identical. The sp
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