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.

THE DEFINITIVE DESIGN AND CONSTRUCTION INDUSTRY SOURCE FOR BUILDING WITH WOOD NOW IN A THOROUGHLY UPDATED SIXTH EDITION Since its first publication in 1966, Timber Construction Manual has become the essential design and construction industry resource for building with structural glued laminated timber. Timber Construction Manual, Sixth Edition provides architects, engineers, contractors, educators, and related professionals with up-to-date information on engineered timber construction, including the latest codes, construction methods, and authoritative design recommendations. Content has been reorganized to flow easily from information on wood properties and applications to specific design considerations. Based on the most reliable technical data available, this edition has been thoroughly revised to encompass: A thorough update of all recommended design criteria for timber structural members, systems, and connections An expanded collection of real-world design examples supported with detailed schematic drawings New material on the role of glulam in sustainable building practices The latest design and construction codes, including the 2012 National Design Specification for Wood Construction, AITC 117-2010, and examples featuring ASCE 7-10 and IBC 2009 More cross-referencing to other available AITC standards on the AITC website Since 1952, the AMERICAN INSTITUTE OF TIMBER CONSTRUCTION has been the national technical trade association of the structural glued laminated timber industry. AITC-recommended building and design codes for wood-based structures are considered authoritative in the United States building industry.