Tests of large bridge columns. . ). This is known to designers as the sec-ondary flexure. (2) There may be rotations of the column at theends due to imperfect end bearings, relative slipping of pin plates,or the overcoming of the pin friction. (3) The integrity of actionof the different shapes is in general not conserved. The stressand strain functions or their derivatives are subject to finite dis-continuities at certain periods of the loading as a result of thelaminated character of the built-up steel, the slipping of pinplates, the irregular action of lattice bars, and transverse dia-phragm
Tests of large bridge columns. . ). This is known to designers as the sec-ondary flexure. (2) There may be rotations of the column at theends due to imperfect end bearings, relative slipping of pin plates,or the overcoming of the pin friction. (3) The integrity of actionof the different shapes is in general not conserved. The stressand strain functions or their derivatives are subject to finite dis-continuities at certain periods of the loading as a result of thelaminated character of the built-up steel, the slipping of pinplates, the irregular action of lattice bars, and transverse dia-phragms, the effects of initial strain of fabrication. It is the purpose to determine from the test data as far as ispracticable the relative weight of influence of the different factors2820°—18 7 9« Technologic Papers of the Bureau of Standards which modify the curve of initial eccentricity. The theoreticallaw of variation of the maximum stresses in an ideal column ofknown initial eccentricity will first be treated as the norm or. f 3o -f /*U/ fy = Maximum or Minimum Stress Fig. 62.—Normal stress distribution in the ideal column with square ends by the laws standard of comparison. The departures of the test columnsfrom this ideal case will be discussed later in the text. (c) Law of Stress Distribution for the Ideal Case.—The columnshown diagramatically in Fig. 62 is supposed to be perfectlyelastic and continuous in structure within the interval of working Tests of Large Bridge Columns 99 stress 0 < / < /w, o<p<pw. It is assumed to have a uniform squarebearing at the upper end and a pin bearing at the lower no deflection was observed in the interval of working stress,the column will be considered for the purpose at hand to be per-fectly restrained at the ends in this interval. The average slen-derness ratio of the test columns is 30, the maximum value being 44. The value of - = 100 has been used in drawing the following atm ec curves. The mean value of t
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