Six glued-laminated beams, 9 inches wide by 31 1/2 inches deep by 50 feet long, containing 21 Douglas-fir laminations, were evaluated. Three beams, designated as clear, were designed as clear straight-grained wood beams and three were designed as structural beams containing strength-reducing characteristics as could be found in commercially produced laminated beams. The average modulus of rupture and modulus of elasticity for clear beams were 8,400 and 2,090,000 pounds per square inch, respectively, and for structural beams were 4,450 and 1,930,000 pounds per square inch. The average strength of the clear beams was within 2 percent of that estimated by a size-effect relationship recently published. The average strength of structural beams was about one-third less than that given by the I sub K/I sub G concept. The modulus of elasticity for all beams was within the range expected of Douglas-fir beams. These results should lead to new design procedures to account for the effect of size on the bending strength of wood beams. The study also indicates the need for further research to obtain a better understanding of the effect of knots on the strength of laminated beams.

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: 16 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00096572
  • Record Type: Publication
  • Source Agency: Association of American Railroads
  • Report/Paper Numbers: ER-72
  • Files: TRIS
  • Created Date: Jul 24 1975 12:00AM