NONDESTRUCTIVE EVALUATION OF MODULUS OF ELASTICITY OF SOUTHERN PINE LVL - EFFECT OF VENEER GRADE AND RELATIVE-HUMIDITY

Nondestructive testing (NDT) methods, stress-wave propagation, and tra nsverse vibration were used to evaluate the modulus of elasticity (MOE ) of laminated veneer lumber (LVL). Five types of LVL, fabricated with southern pine veneers of B, C, and D grades and liquid phenolic forma ldehyde adhesive, were tested flatwise at environmental conditions of 65% and 95% relative humidity (RH) and 75 degrees F (23.9 degrees C) t o examine the influence of veneer grade and RH on some nondestructive mechanical properties of LVL. All LVLs, 1.5 in. (3.81 cm) thick x 3.5 in. (8.89 cm) high x 96 in. (243.84 cm) long, consisted of 13 plies of southern pine veneer, and their structural designs were: (I) all B gr ade veneers, (II) 2 plies of B grade veneer on both faces and all C gr ade veneers in the core plies, (III) 2 plies of B grade veneer on both faces and all D grade veneer in the core plies, (IV) all C grade vene ers, and (V) all D grade veneers. Results indicated that MOE of LVL pr edicted by NDT was influenced by the veneer grade, and specimens fabri cated with better grade veneers showed a higher value of MOE. A signif icant decrease in the MOE determined by both NDT methods was found whe n RH increased from 65% to 95% at 23.9 degrees C (75 degrees F). The M OE measured by the stress-wave method was found to be more sensitive t o the RH change than that determined by the transverse-vibration metho d. A lognormal distribution accurately described the distributions of MOEs determined by both nondestructive methods at both RH levels. As e xpected, a significant increase in moisture content (MC) in the LVL re sulted from increasing RH levels. However, changes in densities of the tested materials due to the RH changes were found to be smaller. Resu lts also indicated that regardless of the RH level, MOE determined fro m the stress-wave test was consistently higher than that obtained from the transverse-vibration test. For comparison, the results of tests o n southern pine No. 1 and No. 2 grade lumber, commonly used in light-f rame construction, are also presented. Analysis of the correlation bet ween the static bending and NDT MOEs was made and results suggested th at edgewise static bending MOE of LVL can be predicted with reasonable accuracy by the stress-wave testing. Good correlations were not obser ved between the edgewise static bending MOE and the nondestructive MOE evaluated by flatwise transverse vibration. However, excellent correl ations between static bending and both NDT MOEs were observed in south ern pine dimension lumber. Correlations between the MOEs evaluated by both nondestructive methods were found to be fair for LVL specimens.