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Fire performance of loadbearing walls with fingerjoined studs

https://library.fpinnovations.ca/en/permalink/fpipub42137
Author
Richardson, L.R.
Date
March 1902
Material Type
Research report
Field
Sustainable Construction
Author
Richardson, L.R.
Contributor
Canada. Canadian Forest Service
Date
March 1902
Material Type
Research report
Physical Description
28 p.
Sector
Wood Products
Field
Sustainable Construction
Research Area
Building Systems
Subject
Resistance
Joints
Series Number
Canadian Forest Service No. 8
Location
Sainte-Foy, Québec
Language
English
Abstract
There are two general categories of fingerjoined lumber in Canada: NLGA SPS-3 “vertical stud use only” and NLGA SPS-1 “structural use”. The latter category is fabricated with phenol-resorcinol-formaldehyde (PRF) adhesive meeting the requirements of CSA O112.7-M1977 or with wood adhesives that meet NLGA “SPS Annex A” requirements. NLGA SPS-1 fingerjoined lumber is considered to be interchangeable with solid-sawn wood of the same species group, grade and size, and accordingly, can be used in either vertical or horizontal applications and under compression, tension or bending loads. NLGA SPS-3 “vertical stud use only” fingerjoined lumber may only be used in “dry service” conditions and vertical applications under axial (or near axial) compression loads, and with bending and tension loads (e.g. wind or earthquake) limited to short duration only. Two types of adhesives are accepted for use in the manufacture of “vertical stud use only” fingerjoined lumber: polyvinyl acetate (PVA) meeting the specifications of CSA O112.8-M1977 Type I and ASTM D 25559 without creep evaluation, and diphenylmethane di-isocyanate based products (also called MDI, isocyanate or polyurethane adhesives). The use of glulam timber beams and columns has a long history and their fire performance has been well documented. Since NLGA SPS-1 fingerjoined lumber products were traditionally manufactured with the same PRF adhesives used in glulam timbers, there was little reason for building and fire officials to be concerned about the fire resistance of this “glued” product. On the other hand, PVA adhesives are thermoplastic products that creep and lose their bond strength at elevated temperatures. While they are thermosetting polymers, isocyanate adhesives chemically decompose at elevated temperatures. In theory, neither effect should be a problem since studs are subjected to axially-applied compressive structural loads. However, the simple fact that the adhesives used in the manufacture of some fingerjoined lumber products could melt or chemically breakdown at elevated temperatures raised concerns about all fingerjoined lumber in the minds of building and fire officials. In an effort to alleviate some of those concerns, a small exploratory project was carried out to examine the performance of fingerjoined lumber exposed to sub-charring temperatures and tension loads, and the fire resistance of gypsum-board-protected wood-frame walls constructed with fingerjoined studs. While only a limited number of specimens of each type of fingerjoined lumber were utilised in this study, the moduli of elasticity (MOE) of those studs were far greater than the “modulus of elasticity for design of compression members” assigned by CSA-O86-01 for the respective grades. Depending upon the grades of fingerjoined lumber and adhesives used in their manufacture, the MOE of between 60 and 95% of the pieces were greater than the “specified modulus of elasticity” assigned by CSA-O86-01. Many building officials believe that while the strength properties of fingerjoined studs are more consistent, their average strength properties are less than those of solid-sawn wood studs of identical grade, species and size, and therefore, the fire resistance ratings of walls constructed with fingerjoined studs may not be as great as those for walls constructed with conventional wood studs. While admittedly limited to an evaluation of MOE of a very small “population size” (20-24 specimens of each material), the data generated in this study does not support their contention. SPF No. 1 and No. 2 lumber lost about one-half of its strength in tension when heated to 200ºC and almost two-thirds when heated to 250ºC. Specimens of SPF No. 2 SPS-1 fingerjoined lumber manufactured with a PRF adhesive lost about one-half of their strength in tension when heated to 150ºC and about 60% when heated to 200ºC. SPF No. 3/Stud grade SPS-3 fingerjoined lumber fabricated with an isocyanate adhesive lost about two-thirds of its strength in tension when heated to 150ºC and about three-quarters when heated to 200ºC. SPF No. 3/Stud grade SPS-3 fingerjoined lumber fabricated with PVA lost more than 90% of its strength in tension when heated to 150ºC and essentially all its strength when heated to 200ºC. Based only on the proportion of “wood” and “glue-bond” failure in each separated fingerjoint, one might reasonably conclude that, when exposed to temperatures up to 250ºC, the adhesives in each fingerjoint in SPF No. 2 SPS-1 fingerjoined lumber bonded with a PRF adhesives has as much strength in tension as the wood fibres in the pieces of lumber that the fingerjoints hold together. Similarly, one could conclude that the adhesive in each fingerjoint in SPF No. 3/Stud grade SPS-3 fingerjoined studs fabricated with an isocyanate adhesive has as much strength in tension, when exposed to temperatures up to 200ºC, as the wood in the pieces that the fingerjoints hold together. Finally, this study indicated that even under ambient conditions, the adhesives in each fingerjoint in SPF No. 3/Stud grade SPS-3 fingerjoined studs fabricated with PVA has less strength in tension than the wood in the pieces that the fingerjoints hold together. These observations do not provide any indication about how fingerjoined lumber products perform as studs in a wall during a fire. Therefore, the wood industry should discourage building officials from specifying tension tests at elevated temperatures for acceptance of fingerjoined studs in fire-resistance-rated walls. Intermediate-scale fire resistance tests were carried out on gypsum-board-protected wood-frame walls constructed with solid sawn and with SPS-1 and SPS-3 fingerjoined studs. In each test, failure was due to the studs in the walls bowing out of the plane of the wall and away from the fire. The amount of bowing was sufficient that the walls were forced out of the furnace frame at mid-height, and hot fire gases could escape from the furnace between the specimen frame and the outer studs in the walls. However, the bowing was only noticeable during the last three or four minutes of the tests. Most importantly, in no case was there an abrupt collapse of the wall: only a continually increasing amount of bowing outwards by the studs during the final minutes. Fear of the sudden collapse of a wall with no obvious indications of its impending failure is the catastrophic event that had originally raised concerns in the minds of building and fire officials about fingerjoined studs. This phenomenon was not observed during any of the tests on walls constructed with fingerjoined studs. The fire resistances of walls constructed with SPF No. 2 SPS-1 (PRF) and SPF No. 3/Stud grade PS-3 (isocyanate adhesive) fingerjoined lumber were not significantly different from that of a wall constructed with solid-sawn SPF No. 1 and No. 2 lumber. The primary goal of this research was to determine if there might be any foundation for the concerns of building and fire officials about the fire performance of wood-frame walls constructed with fingerjoined studs. None were identified. However, the performance of walls constructed with SPS-3 (PVA) fingerjoined studs in the intermediate-scale fire-resistance tests requires additional research since all the fingerjoints in those studs separated during the “non-standard” tests used in this study. The limited resources available for the study (it was only intended to be an exploratory study), resulted in some issues related to the fire performance of fingerjoined lumber not being investigated (hose-stream tests) and a number of others being investigated using non-standard testing procedures (intermediate-scale fire-resistance tests) and limited numbers of specimens (strength in tension at elevated temperatures). Furthermore, whenever fingerjoined lumber is used in fire-rated construction in the USA (e.g. wood-frame apartment buildings and many non-residential buildings), the loadbearing walls of those buildings must have one-hour fire-resistance ratings. Therefore, a committee composed of representatives from major manufacturers of fingerjoined lumber, the committee responsible for writing NLGA standards for fingerjoined lumber, and researchers from Forintek should be convened to review the results of this study and to establish future directions for the wood industry to take when addressing the concerns of building and fire officials about the fire performance of wood-frame walls constructed with fingerjoined studs, and of fingerjoined lumber in general.
Fire resistance
Glued joints - Finger
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Waferboard exposed to rain (a case study)

https://library.fpinnovations.ca/en/permalink/fpipub40045
Author
Szabo, T.
Date
1978
Material Type
Research report
Field
Sustainable Construction
Author
Szabo, T.
Date
1978
Material Type
Research report
Physical Description
7 p.
Sector
Wood Products
Field
Sustainable Construction
Research Area
Building Systems
Subject
Weathering
Waferboard properties
Series Number
55-57-036
E-985
Location
Ottawa, Ontario
Language
English
Abstract
Waferboard - Properties
Waferboard - Testing
Rain
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