Exposed Wood in Fire Resistive Applications

Transcription

1 Please add relevant logo here Exposed Wood in Fire Resistive Applications David Barber, Arup Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.

2 The Wood Products Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516. Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-aia members are available upon request. This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

3 Course Description For buildings, the fire resistance of structural elements is a code-stipulated requirement often dictated by the construction type chosen rather than building materials used. Wood structures are unique in that they can be unprotected while still providing a level of fire resistance. However, both designers and jurisdictions tend to be unfamiliar with this approach. This presentation will cover the use of a variety of exposed structural wood products (solid sawn lumber, nail laminated wood, glue laminated wood and cross laminated wood) in different fire-resistant applications for construction Types III, IV and V. Discussion will include implementation of char calculations, considerations for connections, and information on when calculations or fire tests are required for proving fire resistance in these scenarios. With a better understanding of the challenges and potential solutions, attendees will be able to confidently pursue exposed wood for their projects.

4 Learning Objectives 1. Review provisions of the International Building Code specific to the use of unprotected wood products in fire-resistive members and assemblies. 2. Discuss calculation of fire resistance for exposed wood members, including applicability of char calculations. 3. Highlight options and configurations for connections in fire resistance-rated exposed wood systems. 4. Explore design paths for proving fire resistance acceptability of exposed wood systems, including the use of alternative design methods and materials.

5 Content Why wood? IBC Requirements Fire fundamentals Applications to code compliant buildings Details Summary USDA:

6 Why wood? Sustainability Aesthetics, Innovation Changing technology Efficient construction Prefabrication

7 Current approach CLT Glulam NLT Structural composite lumber (LVL, LSL, PSL)

8 Wood Construction and the IBC Combustible construction Type III, IV, V Non-combustible construction Type I, II Wood is combustible construction Code compliant use in Types III, IV, V

9 Wood Construction and the IBC Type III: Up to 6 stories (B), 5 stories (R) 1 hr FRR load bearing frame 2hr FRR load bearing external walls Type IV: As for Type III, but using heavy timber Type V: Low rise, few restrictions

10 What Does a Type III Building Look Like? The Wood floors and framing (interior) Up to 6 floors, with sprinklers Podium construction with concrete to lower floors Exterior walls are non-combustible, or wood covering (to 40ft) or FRT wood (to 60ft) 10 Duratherm Presentation

11 What Does a Type IV Building Look Like? Up to 6 floors, with sprinklers Wood beams, columns, floors, roof permitted Exterior walls are noncombustible, or FRT wood 11 Duratherm Presentation

12 A Modern Type IV Building Up to 6 floors, with sprinklers Exposing the wood Use of steel or concrete, where appropriate (hybrid construction) Glulam beams, columns; CLT floors and walls 12

13 Wood Construction and the IBC Types III, IV, V wood can be exposed

14 What is a Fire Resistance Rating? Structural resistance Integrity Insulation (from CLT Handbook, US Edition )

15 What is Interior Finish Flammability? Resistance to flame spread and a measure of smoke development - classes A, B and C ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials ( Steiner tunnel ) From Nordic

16 What is Interior Finish Flammability? Type IV - exempt Wood = Class C Some wood will achieve Class A AWC Design for Code Acceptance 1 Flame spread performance of wood products used for interior finish

17 Exposed Wood and Fire - Questions?

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19 All materials are vulnerable to fire:

20 Combustibility - Just another engineering problem? APA

21 Wood - Fire fundamentals Charring Well understood and researched Schaffer, 1966, Forest Products Laboratory

22 Wood - Fire fundamentals Determination of charring rates History of fire tests: Standard furnace tests Tests in real fires Carried out internationally Correlations based on density, moisture, grain direction, sawn or engineered wood Figure 2-2 from TR-10

23 Wood - Fire fundamentals Wood performance in fire is predictable Load carrying under fire is reliable Design for fire resistance, through increasing wood cover Wood has inherent passive fire protection

24 Wood - Fire fundamentals Design char rate increased by 20%: Corner rounding Fissures Zero strength layer behind the char For 1hr exposure = 1.8in/hr For 2hrs = 1.58in/hr From APA

25 Wood - Fire fundamentals 90 minute FRR fire test on 270mm x 415mm glulam beam (from APA)

26 Wood - Fire fundamentals Calculating an FRR What is the area (b x d) needed? What additional wood cover is required, for an FRR (B x D) The difference (B b) is the sacrificial char layer TR-10 Fig 1-2

27 Wood Fire guidance FRR of wood NDS Chapter 16 Method explained in detail in TR-10 TR-10 is a compliant methodology for providing exposed wood FRR

28 Wood Fire calculations Glulam, LVL, sawn lumber Follow NDS CLT Follow NDS IBC NDS TR-10 Section Chapter 16 Part 3

29 Exposed Wood Not all authorities are supportive of exposed wood Sometimes an alternative materials submission is required to support use Significant variance in interpretation of the IBC, with regard to exposed wood Type IV construction is the most straightforward approach

30 Connections Can be expressed where no fire rating is required Where exposed and need a 1 hr FRR: Concealed steel plates Concealed bolts or dowels

31 FRR Connections Design to conceal the whole connection Provide bearing connections From Simpson Strongtie Some connections will need detailed analysis From ETH Fire testing for proprietary off the shelf connections is occurring

32 CLT Connections Proven through fire testing Lap splice From KLH Spline splice

33 CLT A panelized system for walls and floors Similar to concrete flat slab construction - no concealed spaces Highly accurate construction All pre-cut and delivered to site Screw-fixed into place Very strong and very durable

34 Fire Modelling Fire Resistance Ratings β = 1.5 /hr β = 3.0 /hr 1 β = 1.5 /hr β = 3.0 /hr 1 β = 1.5 /hr

35 Exposed Wood in Tall Buildings What can be engineered? Understanding wood performance in fire Using existing research and test data Engineered calculations Encapsulation methods From decoi Architects

36 Questions? This concludes The American Institute of Architects Continuing Education Systems Course David Barber Arup