Fiber stress values for design of glulam timber utility structures

Abstract

In this study, we developed a simple equation to calculate average fiber stress values for design of glued-laminated (glulam) timber utility structures as a function of design bending stress. We took design stress in bending values specified by the American Institute of Timber Construction (AITC) for various combinations of glulam timber, applied appropriate end-use adjustments, and determined an appropriate factor to obtain average modulus of rupture. Fiber stresses for glulam were then determined from the average modulus of rupture values using the relationship between these values and the fiber stress values for round timber poles. To verify this relationship, a data base was compiled that contained bending strength results of glulam timber beams manufactured following the design combinations established by the AITC. Results indicate that the proposed equation can be used to calculate fiber stresses for all glulam beams manufactured with visually graded or E-rated lumber. For bending members less than 50 ft (15.24 m) long, the average fiber stress was found to be approximately 2.7 times the design stress in bending.

Citation

Hernandez, R.; Moody, R. C.; Falk, R. H. Fiber stress values for design of glulam timber utility structures. (Research paper FPL ; RP-532):23 p. : ill. ; 28 cm.