Strain Rate-Dependent Behavior of Laminated Strand Lumber

STRAIN RATE-DEPENDENT BEHAVIOR OF

LAMINATED STRAND LUMBER

By William Donald Syron

Thesis Advisor: Dr. Roberto Lopez-Anido, P.E.

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Civil Engineering)

August, 2010

Over the past several years, researchers at the University of Maine’s Advanced Structures and Composites Center (AEWC) have developed a blast-resistant wood composite structure to replace the existing structures used for the temporary housing of United States Army personnel during long-term deployments.  The damage modes seen in the connections of the blast-resistant building during the most recent blast tests have shown the need to better understand the effect of strain rate on material behavior. 

The rate at which a material strains can have a significant effect of material response.  Due to the observed damage modes and interest in a new material, an alternative high performance wood composite material, Laminated Strand Lumber (LSL), was selected for this research.

The objective of this research was to study the strain rate effects on the modulus of elasticity and strength values of LSL.  Two different grades of LSL (1.35E and 1.75E) were tested in tension and compression over a range of strain rates from 1E-5 to

1E-1 sec^-1.  Compression tests were conducted in the longitudinal and transverse directions of the material while uniaxial tension tests were conducted in the longitudinal direction only.

The results of the experimental testing show that there is no strain rate effect in either the longitudinal modulus of elasticity or strength of the LSL in tension.  The longitudinal compressive strength of the LSL increased by 37% and 31% for the 1.35E and 1.75E grade LSL respectively, while the transverse compressive strength increased by 41%and 16%.  No statistical increase in E_L was observed for the 1.35E grade LSL while an increase of 16% was noted for the 1.75E grade LSL between 1E-5 and

1E-3 sec^-1.  The transverse modulus of elasticity increased by 28% and 18% for the 1.35E and 1.75E grade LSL respectively.  It was determined that the changes in E_L may be affected by the variable density of the LSL.  Recommendations for improving the testing procedure for future testing are given.

In addition to the experimental testing, a simple mechanics based model was used in an attempt to predict the effect of strain rate on the modulus of elasticity of LSL at strain rates higher than those tested in the laboratory.