Structural fire performance of unprotected floor assemblies used in single family houses

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https://doi.org/10.4224/20374231

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Structural fire performance of unprotected floor assemblies used in single family houses

Bénichou, N.; Su, J. Z.; Bwalya, A. C.; Lougheed, G. D.; Taber, B. C.; Leroux, P.

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Structural Fire Performance of Unprotected

Floor Assemblies Used in Single Family

Houses

Ottawa Fire 2010 Symposium 20 May 2010

Noureddine Bénichou, Joseph Su, Alex Bwalya, Gary Lougheed, Bruce Taber, Patrice Leroux

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Outline

Background

Objectives

Experimental Program and Results

Key Findings

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Advent of new materials and innovative products

and systems used in construction of houses

Need to better understand performance and

impact on occupants life safety under fire

conditions

Canadian codes and materials commissions

requested NRC to undertake this research

Title of the project “Fire Performance of Houses”

Background

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Objectives

To better understand

• the factors that affect life safety of occupants

• the impact of residential construction products and systems on life safety of occupants

in single-family houses in the event of a fire

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Research on Fire Performance of Houses

Research studies include a number of phases

Phase I – basement fires with unprotected floor assemblies

• To study impact on the ability of occupants on upper storeys to

escape in the event of a basement fire

– fire development

– smoke movement & tenability conditions

– structural integrity of unprotected floor assemblies

• To determine the sequence of fire events

– fire initiation

– smoke alarm activation

– onset of untenable conditions

– failure of floor assembly above the basement

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Experimental Program - Test Facility

A full-scale test house simulating a two-storey

detached single-family house with a basement

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Experimental Program - Basement

Thermocouples CO / CO2 / O2 Smoke Alarms Air Velocity Pressure Video Legend

Relatively severe, fast-growing fire to challenge the floor

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Experimental Program –

Unprotected Assemblies used as Ceiling

Ottaw Fire 2010 Symposium

Solid wood joists Wood I-joists (LVL flanges) Wood I-joists (FJL flanges)

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Experimental Program - First Storey

Legend Thermocouples CO / CO2 / O2 FTIR Smoke Alarms Smoke Density Air Velocity Pressure Video State of doorway to basement:

• Open • Closed

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Experimental Program

Loading on Floor Assembly

OSB Subfloor

0.95 kPa imposed load (20 psf, i.e. ½ NBC design load)

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Experimental Program

-S

econd

Storey

Ottaw Fire 2010 Sy mposium

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Openings and their States

One window in basement (initially closed)

Basement staircase door open or closed

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Sequence of Events (Fire Scenario)

Ignition of the sofa

Development of fire in basement

Open basement window when:

• _{Temp. at window reaches 300°C}

Open first storey exterior door after 3 min from ignition

Test termination

• Excessive flame penetration through the floor

• Structure failure of the floor

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Experimental Results

Flames at the window

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Experimental Results - Fire Scenarios

Basement NW quadrant. Time (s) 0 200 400 600 800 1000 T e m per atur e ( ºC) 0 200 400 600 800 1000 FS-1 UF-01 UF-03 UF-04 UF-05 UF-06 UF-06R UF-06RR UF-07 Basement NW quadrant Time (s) 0 200 400 600 800 1000 T e m per atur e ( ºC) 0 200 400 600 800 1000 FS-4 UF-02 UF-08 UF-09

open basement doorway closed basement doorway

Temperatures in basement fire room at 2.4 m height

Relatively severe, fast-growing fire in the basement

Very reproducible fire exposure

Challenge to the structural integrity of unprotected floor systems

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Smoke alarm location Basement fire room 1st _storey ₂nd _storey corridor 2nd _storey bedroom (open) 2nd _storey bedroom (closed) type I P 2 I 3 P 4 I 5 P 6 I 9 P 10 I 7 P 8

Tests with open basement doorway

Test UF-01 - 40 75 85 125 135 140 150 200 205 Test UF-03 - 48 58 73 123 133 143 143 218 228 Test UF-04 - 30 65 85 115 130 160 225 230 250 Test UF-05 - 45 40 55 130 145 155 165 245 275 Test UF-06 - 45 75 85 115 125 130 200 230 255 Test UF-06R - 38 58 78 113 123 138 163 198 223 Test UF-06RR - 43 73 78 128 138 143 153 223 248 Test UF-07 - 50 40 55 110 130 130 145 190 210

Tests with closed basement doorway

Test UF-02 - 42 72 97 172 182 212 n.a. 427 541

Test UF-08 - 50 85 95 205 205 220 210 515 515

Test UF-09 - 44 79 89 179 179 209 204 479 459

Experimental Results - Smoke Alarm

Responses

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NFPA Conference Session T24, June 9, 2009

Tenability Analysis – temperature measurements

closed bedroom 200 400 600 800 open bedroom 200 400 600 800 2nd storey corridor 200 400 600 800 1st storey SW quadrant Time (s) 0 100 200 300 400 500 0 200 400 600 800

UF-06R _{closed bedroom}

200 400 600 800 open bedroom 200 400 600 800 2nd storey corridor 200 400 600 800 1st storey SW quadrant Time (s) 0 200 400 600 800 1000 0 200 400 600 800 UF-09 T emperature (ºC) T emperature (ºC)

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Experimental Results - Structural Response

of Floor Assemblies

TCs under insulated pads on subfloor Te mpe rature (ºC) 0 100 200 300 400 500 600 700 800 Flame sensors at subfloor T&G joints

Volt s 0.0 0.5 1.0 1.5 2.0 Floor deflections at 9 points Time (s) 0 100 200 300 400 500 De flection (mm) -700 -600 -500 -400 -300 -200 -100 0

Measurements on floor assembly to determine time to floor failure

• Temperatures

• Flame penetration

• Deflections

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Experimental Results - Structural Response

of Floor Assemblies

Deflection prior to floor failure

a) Tests with open basement doorway Time (s) 0 100 200 300 400 500 600 700 Def lect ion ( mm) -350 -300 -250 -200 -150 -100 -50 0 UF-01 UF-03 UF-04 UF-05 UF-06 UF-06R UF-06RR UF-07

b) Tests with closed basement doorway Time (s) 0 100 200 300 400 500 600 700 Def lect ion (mm) -350 -300 -250 -200 -150 -100 -50 0 UF-02 UF-08 UF-09

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Experimental Results - Primary Mode of

Failure of Floor Assemblies

Solid wood joist assemblies

• subfloor failure (burn through)

• most of the joists charred but still in place

Engineered floor assemblies

• joist or truss failure

• collapse into the basement

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Experimental Results - Primary Mode of

Failure of Floor Assemblies

Solid wood joist assemblies: subfloor failure (burn through)

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Experimental Results - Primary Mode of

Failure of Floor Assemblies

Wood I joists A and B: web materials burned through

Wood I-joist B: breakdown at finger joints of lumber flanges

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Experimental Results - Primary Mode of

Failure of Floor Assemblies

Steel C-joists: lost strength and deformed

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Experimental Results - Primary Mode of

Failure of Floor Assemblies

Metal-web & metal-plate wood trusses: metal-wood connections

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Time (s)

0 200 400 600 800 1000 1200 1400

onset of untenable conditions

smoke alarm activation

initiation of fire 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400

floor not usable for egress

Solid wood joist

Wood I-joist A

Steel C-joist

Metal-plate wood truss

Wood I-joist B

Metal web wood truss

open

basement

doorway

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onset of untenable conditions

smoke alarm activation

initiation of fire

0 200 400 600 800 1000 1200 1400

floor not usable for egress

Open 0 200 400 600 800 1000 1200 1400 Closed 0 200 400 600 800 1000 1200 1400 Open 0 200 400 600 800 1000 1200 1400 Closed (s) 0 200 400 600 800 1000 1200 1400 Open 0 200 400 600 800 1000 1200 1400 Closed

a) Solid wood joist

b) Wood I-joist A

c) Metal web wood truss

(s) (s) Comparison: open vs. closed basement doorway

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Key Findings

Tests with an open stairwell to the basement

• Fire events followed a chronological sequence:

– initiation of the fire

– activation of smoke alarms

– loss of tenable conditions in open areas on upper storeys

– finally structural failure of the test floor assembly

• Untenable conditions for occupants in open areas on upper storeys were reached:

– at approximately the same time regardless of the type of the test floor assemblies

– before failure of the test floor assemblies occurred

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Key Findings (continued)

Limited tests with a closed door to the basement

3 assemblies: solid wood joist, wood I-joist, metal-web wood truss

• Reduced the rate of fire growth in the basement

• Slowed the transport of combustion products from the basement to the upper storeys

• Delayed the time to reach tenability limits for occupants on upper storeys

• Delayed the times for the test floor assemblies to reach structural failure

• Metal-web wood truss assembly failed before tenability limits were reached in open areas on upper storeys

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Key Findings (continued)

All tests

• The time to reach failure for the engineered assemblies was shorter than for the solid wood joist assemblies

• Untenable conditions were not reached, for the duration of the tests, in the second-storey bedroom where the door to the bedroom was kept closed

• Results support code requirements for interconnected

smoke alarms on each level of a house to alert occupants

• Results reinforce the importance of continued public education on home fire safety

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Acknowledgments

Partners in Phase 1 of the project:

• Canada Mortgage and Housing Corporation

• Canadian Automatic Sprinkler Association

• Canadian Wood Council

• Cement Association of Canada

• City of Calgary

• FPInnovations - Forintek Division

• North American Insulation Manufacturers Association

• Ontario Ministry of Community Safety and Correctional Services/Office of the Fire Marshal

• Ontario Ministry of Municipal Affairs and Housing

• Wood I-Joist Manufacturers Association

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Acknowledgments

NRC-IRC project team:

• J.Z. Su • N. Bénichou • A.C. Bwalya • G.D. Lougheed • B.C. Taber • P. Leroux • G. Proulx • A. Kashef • C. McCartney • J.R. Thomas

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Thank you!

Questions?

Summary http://irc.nrc-cnrc.gc.ca/pubs/fulltext/rr/rr252/rr252.pdf

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Structural fire performance of unprotected floor assemblies used in single family houses

Structural Fire Performance of Unprotected

Floor Assemblies Used in Single Family

Houses

Outline



Background



Objectives



Experimental Program and Results



Key Findings



Advent of new materials and innovative products

and systems used in construction of houses



Need to better understand performance and

impact on occupants life safety under fire

conditions



Canadian codes and materials commissions

requested NRC to undertake this research



Title of the project “Fire Performance of Houses”

Background

Objectives

To better understand

in single-family houses in the event of a fire

Research on Fire Performance of Houses

Experimental Program - Test Facility



A full-scale test house simulating a two-storey

detached single-family house with a basement

Experimental Program - Basement

Experimental Program –

Unprotected Assemblies used as Ceiling

Experimental Program - First Storey

Experimental Program

Loading on Floor Assembly

Experimental Program

-S

econd

Storey

Openings and their States

Sequence of Events (Fire Scenario)

Experimental Results

Experimental Results - Fire Scenarios

Experimental Results - Smoke Alarm

Responses

Tenability Analysis – temperature measurements

Experimental Results - Structural Response

of Floor Assemblies

Experimental Results - Structural Response

of Floor Assemblies



Deflection prior to floor failure

Experimental Results - Primary Mode of

Failure of Floor Assemblies



Solid wood joist assemblies

•

subfloor failure (burn through)

•

most of the joists charred but still in place



Engineered floor assemblies

•

joist or truss failure

•

collapse into the basement

Experimental Results - Primary Mode of

Failure of Floor Assemblies

Experimental Results - Primary Mode of

Failure of Floor Assemblies

Experimental Results - Primary Mode of

Failure of Floor Assemblies

Experimental Results - Primary Mode of

Failure of Floor Assemblies

open