A Vibrational Approach to Nondestructive Testing of Structural Timber

Methods used to predict the mechanical properties of construction lumber using vibration parameters are described. The primary objective of this research was to determine, using both forced and free vibrations, whether energy dissipation parameters are related to mechanical properties in construction lumber. A second objective was to develop a vibrational method and instrumentation suitable for measuring these parameters with adequate accuracy. Inland Douglas-fir joist material in five grades from Select Structural to Economy was used. Nominal 2-inch boards in lengths 12, 14, and 16 feet and widths of 6, 8, 10, and 12 inches were vibrated on edge and flat. The boards were subsequently tested to destruction on edge with third-point loading. The major conclusion is that construction lumber of typical sizes and grades can be successfully vibrated and mechanical properties predicted with reasonable accuracy. Both the equipment and the basic hypothesis regarding vibrational parameters were confirmed. The modulus of elasticity was predicted at a level of accuracy that indicated 96 percent of the variability had been accounted for. The vibrational parameters underlying the prediction of modulus of elasticity. appeared not to be affected adversely by moisture content. The prediction of modulus of rupture was more difficult. The logarithmic decrement was found to be well-correlated with modulus of rupture, but the relationship appeared to be very sensitive to moisture content. Indications are that, in practice, moisture content must be either closely controlled or corrected at time of test. In regard to the prediction of modulus of rupture, length appeared to define distinct populations, but widths, within the range of 6 to 12 inches, appeared to be self-correcting.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member