An investigation of hooped concrete columns . have: A= .0C089p + .00043 fp - ) 10000 Ak - 1 )? C0062p Effect of On page 35A are plotted the averagevalues of the ultimate loads for the columns of the three a study of the average curves for the 5-ft. columns,we find that the average value of the modulus of elasticity fasdetermined by taking a tangent to the longitudinal load-defor-mation curve at a point where the stress in the spiral isbecoming large) for the columns having the three percents ofspiral is about 72,000 lb. per Eulers formula for long columns
An investigation of hooped concrete columns . have: A= .0C089p + .00043 fp - ) 10000 Ak - 1 )? C0062p Effect of On page 35A are plotted the averagevalues of the ultimate loads for the columns of the three a study of the average curves for the 5-ft. columns,we find that the average value of the modulus of elasticity fasdetermined by taking a tangent to the longitudinal load-defor-mation curve at a point where the stress in the spiral isbecoming large) for the columns having the three percents ofspiral is about 72,000 lb. per Eulers formula for long columns is where E has the value for round ended columns an3 «f- for fixed ended columns. If we assume that the degree of fixity of the ends of these columns is such that the value of should be 3, 3 77*Efl/r)s then we have the formula p a- = for the additional strength of the columns due to the spiral reinforcing. Takingthe value of E as given above, then for the three lengths of5—ft., 10—ft., and 20—ft, we have the following values for. 5580., 1320, 330 If it is assumed thatthis formula does not apply to the 5ft. columns, then these val-ues may he approximately correct. But from a study of the aver-age curves, as well as from theoretical considerations, itseems that the value of E is not a constant, hut depends uponthe length of the column, ith this in mind, it hardly seemsthat the added strength can he represented by a formula of theform of Rulers, hile variations in the amount of spiral havelittle effect upon the strength of the 20-ft. columns, theycertainly do affect the strengths of the 10-ft, and 5-ft. col-umns, and it seems that any formula for calculating the ad-jedstrength should te^re account of these facts. Effect Of Amount of The relation between theultimate strength of the column and the amount of spiral isshown for the 5-ft. columns of 1-2-4 concrete by the lower curveon page 752. From this curve we see that r of spiral adds anaverage of
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