exposed wood in fire resistive applications...please add relevant logo here exposed wood in fire...

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.

“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.

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Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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.

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.

Content

� Why wood?

� IBC Requirements

� Fire fundamentals

� Applications to code compliant buildings

� Details

� Summary

USDA: www.tallwoodbuildingcompetition.org

Why wood?

� Sustainability

� Aesthetics, Innovation

� Changing technology

� Efficient construction

� Prefabrication

Current approach

CLT

Glulam

NLT

LVL

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

Wood Construction and the IBC

Type III:

• Up to 6 stories (B), 5 stories (R)

• 1 hr FRR load bearing structure

• 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

Duratherm Presentation

Podium construction with

concrete to lower floors

Wood floors and

framing (interior)

Exterior walls are non-combustible, or wood

covering (to 40ft) or FRT wood (to 60ft)

Up to 6 floors, with sprinklers

11

What Does a Type IV Building Look Like?

Duratherm Presentation

Exterior walls are non-

combustible, or FRT wood

Up to 6 floors, with sprinklers

Wood beams, columns, floors, roof permitted

12

A Modern Type IV Building

Exposing the wood

Up to 6 floors, with sprinklers

Glulam beams, columns; CLT floors and walls

Use of steel or concrete, where

appropriate (hybrid construction)

Wood Construction and the IBC

Types III, IV, V – wood can be exposed

What is a Fire Resistance Rating?

Structural resistance Integrity Insulation(from “CLT Handbook, US Edition”)

What is Interior Finish Flammability?

Resistance to flame spread and a measure of

smoke development - classes A, B and C

From Nordic ASTM E84 “Standard Test Method for Surface Burning

Characteristics of Building Materials (‘Steiner tunnel’)

What is Interior Finish Flammability?

Type IV - exempt

Wood = Class C

Some wood products will achieve B

AWC Design for Code Acceptance – 1 “Flame spread performance of wood products used for interior finish”

Exposed Wood and Fire

- Questions ?

Exposed wood and fire:What are the issues?

All materials are vulnerable to fire:

Combustibility - Just another engineering problem?

APA

Wood - Fire fundamentals� Charring

� Well understood and researched

Schaffer, 1966, Forest Products Laboratory

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

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

Wood - Fire fundamentals

Long term (nominal) char rate = 1.5 in/hr

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

Wood - Fire fundamentals

90 minute FRR fire test on 270mm x 415mm glulam beam (from APA)

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

Wood – Fire guidance

FRR of wood – NDS Chapter 16

Method explained in detail in TR-10

Part 3 provides all required design

information

TR-10 is a compliant methodology for

providing exposed wood FRR

Wood – Fire calculations

� Glulam, LVL, sawn lumber Follow NDS

� CLT Follow NDS

� IBC NDS TR-10Section 722.1 Part 3Chapter 16

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

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

FRR Connections

Design to conceal the whole connection

Provide bearing connections

Some connections will need detailed

analysis

Fire testing for proprietary “off the shelf”

connections is occurring

From Simpson Strongtie

From ETH

CLT Connections

Proven through fire testing

Lap splice

Spline splice

From KLH

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

CLT - Fire fundamentals

Does it char like normal wood?

What is delamination?

Is all CLT constructed the same?

Fire Modelling – Fire Resistance Ratings

1”

1”

β = 1.5”/hr

β = 1.5”/hr

β = 3.0”/hr

β = 1.5”/hr

β = 3.0”/hr

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

Questions?

This concludes The American Institute of Architects Continuing Education Systems Course

David Barber

Arup

david.barber@arup.com