Explanation of tension-side notch design provisions for glulam in CSA Standard 086-14

Abstract

Traditionally unreinforced tension-side notches at supports of glued-laminated-timber (glulam) bending members have been designed in Canada assuming shear capacity is reduced in proportion to the square of the residual depth ratio. The origin of that practice lies in World War II era studies in the USA on solid wood members. More recent research in Canada, US, and Europe has focussed on application of linear elastic fracture mechanics (LEFM) methods to such problems, reflecting that such approaches can account for effects of variables other than notch depth ratio. Canadian wood design code CSA Standard 086 “Engineering Design in Wood” first capitalized on availability of LEFM approaches in 1994 by adopting such a method for design of sawn lumber members with tension-side notches at supports. The same was not done then for glulam members because of paucity of supporting test data. That gap has now been filled and the 2014 edition of CSA Standard 086 employs consistent LEFM based design approaches for both sawn lumber and glulam members with tension-side notches. New provisions for glulam recognize influences that notch length and shape, and how laminations in members are fabricated have on member capacities. Discussion here addresses the logic that underpins the new glulam provisions and how application of those provisions impacts design solutions. Overall impact of the new design provisions is to discourage use of relatively large tension-side notches at supports of larger glulam bending members, while not discouraging use of notches in smaller glulam members.