Strength of Wood Columns

The load-carrying capacity or buckling load of columns was studied by testing 20 eastern spruce columns of rectangular cross-section and with varying slenderness ratios. The specimens were clear, free from defects, and had a moisture content of 12 percent plus or minus 1 percent. The tests were performed using spherical bearings to insure pin-end conditions. The buckling load was the load at which strain reversal started on one side of the column. The strain reversal was measured by electric strain gages mounted on opposite sides at the midspan of a column. The tangent modulus buckling load and the failure load were coincident for most of the inelastic columns. The test results in the inelastic range of stress are close to Engesser’s curve and, hence, the author believes that the inelastic behavior of an axially loaded column can be satisfactorily predicted by the use of Engesser’s formula, provided a well-defined compression stress-strain curve is available. In this study, a first auxiliary stress-strain curve was determined from compressive tests on ASTM standard specimens. An electrical strain recorder was used to record strains at various loads. Individual tangent modulus values were approximated by each successive pair of stress-strain readings by dividing the stress increment by the strain increment.

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