Michael O. Hunt

Mechanical properties of laminated veneer lumber via five-point bending test

The five-point bending test is shown to be an effective and efficient way of determining the mechanical properties of structural composite lumber. Shear strength, bending strength, shear-free Youngs modulus of elasticity and shear modulus for both plank (flatwise) and joist (edgewise) orientations can be obtained with simple adjustments of the test configuration. Span or span-to-depth ratios are adjusted to produce either predominantly shear or bending failure. To determine elastic constants, a removable center support creates the necessary situation for both four-point bending and five-point bending. Use of a deflection yoke is especially important in determining the shear moduli. Results are reported for testing laminated veneer lumber. which was selected as representative of the evolving family of structural composite lumber products.

New Technique for Evaluating Damping of Longitudinal Free Vibration in Wood-Based Materials

Classical log-decrement techniques have been used to evaluate the damping property of materials. However, the consistency and repeatability of the methods when applied to wood and wood-based materials have been found lacking. A different way to view the free vibration of a single-degree-of-freedom system in the x − ˚x plane is presented. A new method that uses all sample points and does not require a knowledge of the initial conditions to determine the damping properties is developed. A comparison between the new method and the classical method is made for three wood-based materials: solid wood, medium density fiberboard (MDF), and particleboard. The results show that the new method is more consistent and repeatable in measuring damping than the classical method. For the six cases examined, there was an absolute average difference of 3.8% in measuring log-decrement between the methods.

Low Frequency Vibration Approach to Assess the Performance of Wood Structural Systems

The primary means of inspecting buildings and other structures is to evaluate each structure member individually. This is a time consuming process that is expensive, particularly if sheathing or other covering materials must be removed to access the structural members. This paper presents an effort to use a low frequency vibration method for assessing the structural performance of wood floor systems.

Use of phase-plot to evaluate damping of free vibration in wood-based materials

Classical log-decrement techniques have been used to evaluate the damping property of materials. However, the consistency and repeatability of the method when applied to wood and wood-based materials has been found lacking. A different way to view the free vibration of a single-degree- of-freedom system in the (chi) -(chi) (DOT) plane is presented. When (chi) and (chi) (DOT)/(omega) d are used to describe the free vibration, it will plot as a spiral curve asymptotically approaching the origin. The radius R of the spiral curve, when plotted in the time domain,is the same as the decay profile curve of the free vibration. Since every sample point has its associated radius, all points of the free vibration can be used to calculate the damping property. This method does not require a knowledge of the initial conditions and is easy to use. Preliminary results show that the new method is more consistent and repeatable in measuring damping than the classical method for wood- based materials.