. Tests of eighteen concrete columns reinforced with cast 9 000 98009360 681 500 930 150 9580 14 14 19 20 630 500679 000 888 500827 500 91508520 654 750 858 000 8835 1 Area Reinforcement Squareinches Per cent .68 Studying the maximum load carried by these columns and theirrelation to the length as plotted in Fig. 19, we find an apparentlyvery definite relation extant. The straight line drawn representsthe plotted points very closely, the average deviation of thepoints from the curve being but per cent, the maximumdifference
. Tests of eighteen concrete columns reinforced with cast 9 000 98009360 681 500 930 150 9580 14 14 19 20 630 500679 000 888 500827 500 91508520 654 750 858 000 8835 1 Area Reinforcement Squareinches Per cent .68 Studying the maximum load carried by these columns and theirrelation to the length as plotted in Fig. 19, we find an apparentlyvery definite relation extant. The straight line drawn representsthe plotted points very closely, the average deviation of thepoints from the curve being but per cent, the maximumdifference of any result from the derived line only 5 per cent. The equation of these lines is P= 1 180 000— 1930/, or dividingby the cross-sectional area of the column inside of the spiral (theconcrete of the shell being totally destroyed and valueless as to pstrength at this point) we obtain the equation -r= 12 150— 4 P=load on column (in pounds). A = area of column within spiral. /=length of column in inches. 3o Technologic Papers of the Bureau of Standards. ;^Stva-iTT-— On.* X){v\%\qtk a=, 0,000a per i-n. 700000 / / 600000 / y » / / / 500 000 / / / / 1/ y> V / 400000 / !/ A / / A ( i / ?/ 300 000 # -t> / / f f / / M / / 200 000 / / f / 1 / / K / 1 / iooooo J r / I 1 y f. / / o, 1 / { ( 1 i —^ / Fig. 18.—Stress strain and load strain diagrams for columns of different lengths and the same cross section Reinforced Concrete Columns 31 The average strength of the concrete as shown by the smallconcrete cylinders was 4060 pounds per square inch, and theincreased strength of spirally reinforced concrete is given by theformula 5= (1 + psC)f in which 5 = the maximum stress withstood by the reinforced concrete, p6 = per cent spiral reinforcement, C = maximum stress withstood by the unreinforced concrete. We can therefore write the probable equation: P -r = 4o6o (i—pc) (1+ pB + 6i, 000 pc — 20 Z, in which J\. pc = per cent cast-iron reinforcement. ps = per
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