Determination of desirable lengths of Z- and channel-section columns for local-instability tests Page: 4 of 14
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NACA RB No. LlO
Stress-strain tests of the material were made with
single-thickness specimens in a roller-tpe compression
fixture similar to that shown in figure of reference 2.
Copres-ive stress-strain curves are shown in figure 2.
The values o' the convopessive yield stress, determined
by the C.2-percent--offset method, and of the modulus of
elasticity are givcn in table 2.
METHOD OF TESTING
The colurnn tests were made in a 300,OO0-pound-
capacity compression testing machine that is accurate
within three-quarters of 1 percent for the rarrnge of load
used in the tests.
A Z-sectibn column under test is shown in figure 3.
The displacement of pointers, supported by extensicn
arms attached to the flanges of the colun.ns, was measured
by the optical micrometers that can be seen in figure 3.
The critical compressive stress was obtained from stress-
distortion curves in the manner described. and illustrated
in reference 3. In this method, the critical stress is
determined as the point near the top of the knee of the
stress-distortion curve where a marked increase in distor-
tion first occurs with small increase in stress.
RESULTS AND DISCUSSION
The variation of o and 0max with L/b , for
each of the different types of column tested is presented
in figure . Columns having - 2L and b 0.5
developed bending failure for - > 7. A definite rise
in critical and maximum stresses when the columns become
very short is shown by these curves. For all except the
very short columns, however, the curves are relatively
level. The number of half-waves of the buckling pattern
that occurred in each case is also indicated in figure 4.
It ]has been found desirable for test purposes to
make the column length such that an odd number of half-
waves.develops, because of the convenience in measuring
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Heimerl, George J. & Roy, J. Albert. Determination of desirable lengths of Z- and channel-section columns for local-instability tests, report, October 1944; (digital.library.unt.edu/ark:/67531/metadc62253/m1/4/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.