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Experimental research on the buckling behaviour of slender prestressed concrete columns Laszlo, Gyorgy

Abstract

Thirty full scale prestressed concrete struts all having a slenderness ratio of L/D = 40 were tested with three different eccentricities. Stress-strain curves of the corresponding test cylinders were established and the Young's Moduli evaluated. The specimens were fabricated with different percentages of prestressing steel ranging from 0.23 to 1.20%. The initial prestressing forces were set to obtain a final prestress of 140,000 psi in all specimens. The dimensions of the struts, and the quality and manufacturing process of the concrete, were kept constant. Special adjustable supporting devices simulated ideal hinged conditions. The struts were tested to their ultimate capacity and their critical buckling loads were evaluated. The tests proved that, provided the column is made of high quality concrete, the critical load values can be obtained by using Euler's fundamental formula, and these values are independent of the amount of prestressing. For eccentrically loaded struts maximum stresses from a modified secant formula, incorporating effect of prestressing, were compared with those calculated on basis of observed deflections. According to the test results the secant modulus corresponding to the average compressive stress should be used in Euler's formula.

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