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Fire resistance

Robert Jansson SP Fire Technology

September 11, 2013 robert.jansson@sp.se

Outline

Fire resistance

Part 1:

• What is fire resistance?

• Behaviour of the main building materials in fire

• Simple design rules

Part 2:

• What is failure?

• Examples of big fire tests

• Design of structures in fire

• Case study

What is fire resistance?

• Loadbearing capacity

• Integrity

• Insulation

• Walls

• Roofs

• Floors

• Ceilings

• Doors

• Windows

• Penetration seals

• Installations

Storey 1

Storey 2

Load bearing floor

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Classification

• R – Loadbearing capacity

The ability of a loaded building element to withstand a fire without loosing its

stability

• E – Integrity

The ability of a building element to prevent passage through it of flames and hot

gases

• I – Insulation

The ability of a building element to restrict temperature rise on the unexposed side

Classification period 15, 30, 45, 60, 90, 120 … [min]

Eg. REI 90

Fire resistance test of loadbearing capacity- R

• Load level provided by the sponsor

• Performance criteria: - Deflection or contraction:

- Rate of deflection or contraction:

Deflection

Contraction

Horizontal element

Vertical element

d

LD

400

2

d

L

dt

dD

9000

2

Fire resistance test of integrity- E

• Flames

• Cotton pad

• Gap gauges

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Fire resistance test of insulation - I

• Maximum temperature rise:

• 140ºC, average

• 180ºC, any location

Furnaces at SP Fire Technology

Horizontal furnace Vertical furnace

Fire curves

0

200

400

600

800

1000

1200

1400

1600

0 30 60 90 120 150 180

Time (minutes)

Tem

pera

ture

(C

)

RWS

HC-curve

Standard curve

• Standard time – temperature curve ISO 834

• Hydrocarbon curve

• RWS: Tunnel fires

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Examples of product - Walls

Loadbearing wall

Non-loadbering wall

Examples of product - Glazed partitions

Door with insulating glass pane

Glazed partitions, EW

Examples of product - Doors

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Fire resistance test of smoke leakage - S

Doors with fire

resistance ability, i.e.

EI xx will not protect

against smoke

leakage

Smoke tight doors

are used in hospitals,

prison cells, hotels

etc.

Examples of product - Penetration seals

Cables

Power cables

Signal cables

The function of the cables shall be maintain during fire exposure

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Common building materials

• Concrete

• Wood

• Steel

None of these materials can withstand an endless fire!

Concrete and fire

• Generally a very fire resisting material

• Well known material characteristics

• Quite simple to design structures for fire exposure (theoretical

methods)

• Can have problems with spalling

• NEW CONCRETES BEHAVES DIFFERENTLY (SCC, HPC…)

Design of concrete structures

• Temperature calculations

• Temperature known → Stresses can be calculated

• Different methods available

– FEM

– Simple handbook methods

– Design charts

– Eurocode 2

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Some temperature dependant properties of concrete

Eurocode 2:

Design of concrete structures – Part 1-2: General rules –Structural fire design

Some temperature dependant properties of concrete

• Compressive strength

Some temperature dependant properties of concrete

• Elasticity

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Some typical behaviour of concrete during heating

• Thermal expansion of

- the cement paste

- the aggregate

Fire spalling of concrete

A loaded beam during a large scale fire test

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Surface spalling

Stockholm 2006

Angered 2007

Heberg 2005

Alingsås 2006

Great Belt 1994

Mont Blanc 1999 Euro tunnel 1996

Severe spalling

St Gotthard 2001

Fire spalling prediction

• Role of thumbs, monograms or theoretical calculations is only

guidance when dealing with SCC or HPC. To be sure fire tests

needs to be performed.

• Remember:

Dangerous fire spalling does not occur in low strength dry

concrete!!

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Other concrete damage

• Cracks, delaminations

Wood Wood is an organic combustible material, its fire properties is

mainly influenced of:

• Dimension

• Moisture content

• Density

• Roughness

Ignition of wood

- In presence of a small flame

10

20

30

40

0

0 10 20 30 40

Time to ignition [min]

Incident heat flux [kW/m2]

Increased moisture content,

Increased density

Rougher surface Low

er l

imit

fo

r ig

nit

ion

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Temperature zones

In slowly heated wood different temperature zones will occurs in

the material.

• Below 200 C

The degradation is slow, in principal CO2 and H2O are released.

• Between 280 – 500 °C

Combustible gases is formed which burns outside the material in

presence of oxygen. Charcoal is formed but will not burn.

• Above 500 °C

Charcoal is formed but burns in the same rate as it forms.

Charing

In a fully developed fire is the charring rate app. 0.6 – 1.0 mm/min.

• Char layer

• Pyrolysis zone

A very thin zone, a few mm

• Normal wood

The temperature and the main part

of the properties are almost

unaffected.

Wood structures will maintain the loadbearing capacity under a

certain time

Example REI 60

• Wood stud 45x120 mm

• Insulation 120 mm

• One layer of 15 mm gypsum

plaster boards on each side.

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Example JAS Approval 45 minutes

• Glue laminated timber beam

• Width x height: 150 x300 mm

• Span: 5.4 m

• Load: app. 2 tons

150

300 F F

Steel

Steel structure

Steel - Thermal conductivity

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Steel - Specific heat

Steel - Thermal elongation

Thermal induced stresses

Mechanical properties

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Protection materials for steel

Boards Intumescent coating

Simplified design methods

• Concrete

• Wood

• Steel

Simplified design methods

• Concrete

• Wood

• Steel

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Simplified design methods

• Wood

• Concrete

• Steel

Questions? For additional information

robert.jansson@sp.se