Fire performance of FRP-strengthened concrete systems

(1)

Publisher’s version / Version de l'éditeur:

Short Course on Response of Materials and Structures to Fires [Proceedings], pp.

1-49, 2009-05-20

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Fire performance of FRP-strengthened concrete systems

(2)

5/12/2009

Short Course

Response of Materials and Structures to Fires

May 20 ‐ 22, 2009

C l t

U i

it Ott

O t i

Fire Performance of

FRP-Strengthened Concrete Systems

Carleton University, Ottawa, Ontario

Strengthened Concrete Systems

Noureddine Benichou

National Research Council of Canada

Industrial Research Chair in Fire Safety Engineering

(3)

5/12/2009

Outline

• Structural Fire Safety

• Fire and FRP Materials

• Fire and FRP Structures

Fire and FRP Structures

• Fire and FRP-Strengthened Concrete

• Recommendations for Design

• Application Cases

Short Course – Response of Materials and Structures to Fires, May 20 – 22, 2009

(4)

5/12/2009

Structural Fire Safety:

The goal is to

limit the probability of death injury and

• The goal is to

limit the probability of death, injury, and

property loss in fire

• Modern codes place the emphasis on

life-safety objectives

• Property protection is left to building owners

Ensure sufficient design consideration given to fire

– Ensure sufficient design consideration given to fire

–

This is rapidly becoming more important…

(5)

5/12/2009

Structures in Fire: “Fire

Resistance”

• Fire resistance is provided in selected members of a

structure

– Ensures that fire and smoke do not spread

– Prevents structural collapse during fire

• Fire Resistance (FR)

– Defined as the time to

“failure” of a member when

subjected to a

“standard fire”

– Evaluation of fire resistance

• Fire testing

• Prescriptive methods

(6)

5/12/2009

What is “Failure”?

Main

failure criteria which define the fire resistance of

• Main

failure criteria which define the fire resistance of

structural members:

1. Loss of load-bearing capacity

• Must resist expected loads in fire

2 Loss of fire separation characteristics

2. Loss of fire separation characteristics

3. ASTM - unacceptable temperature rise

• Reinforcing/structural steel (temperature < 593°C)

• 593°C is the

critical temperature for steel (has

approximately ½ its room temperature strength)

• Unexposed surfaces (average rise < 140°C)

(7)

5/12/2009

Fire and FRP Materials

(8)

5/12/2009

Fibre Reinforced Polymers (FRPs)

Fib

P l

M

i

FRP

Fibres + Polymer Matrix = FRP

• Overall properties depend on:

– Mechanical properties of matrix

– Mechanical properties of fibres

– Fibre volume fraction

– Orientation of fibres

– Fibre‐matrix interaction

– Method of manufacturing

– Size of component

(9)

5/12/2009

e.g. Stress-Strain Response at

Ambient Temperature

3000

2000

2500

3000

(MPa)

₁₅₀

200

250 (ksi)

CFRP

500 1000

1500

Stress

(

50

100

150 Stress

GFRP

Black Steel

0

0.00

0.01

0.02

0.03 Strain

0

(10)

5/12/2009

Applications of FRPs in

Construction

• Internal reinforcement of concrete

– Bridge decks

– Marine structures

– Non‐magnetic applications (medical, communication, etc.)

(11)

5/12/2009

Applications of FRPs in

Construction

• Strengthening concrete steel masonry timber

• Strengthening concrete, steel, masonry, timber

– Flexure

– Shear

– Axial/Confinement

(12)

5/12/2009

FRP characteristics at high

temperature

• Organic nature of polymers Æ

susceptible to combustion

• T

_g

: Glass transition temperature is

p

commonly taken as the performance limit

for the FRP - Typically 70 – 100°C

(13)

5/12/2009

FRPs & Fire: Major Concerns

• Fire is recognized as a

critical research need

for FRP:

–

a primary factor preventing widespread

application of FRPs in buildings

pp

g

• Potential concerns during fire:

1. Loss of strength and stiffness

2. Loss of interaction (bond) w/ concrete

3. Smoke generation and flame spread

(14)

5/12/2009

GFRP: Available Data (2005)

Glass Fibres

Glass FRP Bars

GFRP Rebars

Glass Fibres

Strength

GFRP Rebars

Pullout Strength

Glass FRP Bars

Tensile Strength

(15)

5/12/2009

Recent tests

Differential scanning calorimetry (DSC)

• Differential scanning calorimetry (DSC)

– Polymer resin and FRP composite

– Determine T

_g

• Tension tests on FRP specimens

– Tension tests on FRP coupons

Tension tests on FRP coupons

– Tension tests on single-lap

FRP-to-FRP bond

– Pull-apart bond tests on

FRP-to-concrete bond

> 300 mm

• Compression tests on FRP-wrapped

concrete cylindrical specimens

63.5 mm 63.5 mm

(16)

5/12/2009

Results - strength

• Strength degradation

g

e

1.0

1.2 Tg

(

)

_⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛ +

+

−

⎟

⎠

⎞

⎜

⎝

⎛ −

=

2

1 tanh

2

1 a

c

T

b

a

f

o

σ

T

/

σ

20 ο

C

, Avera

g

0 2

0.4

0.6

0.8 Temperature (oC)

0

50

100

150

200

250

0.0

0.2

(17)

5/12/2009

Failure modes

₁₆

(18)

5/12/2009

Fire and FRP Structures

(19)

5/12/2009

FRP Structures under

Temperatures

All FRP t

t

• All FRP structures

– Thick elements can char and

protect FRP

– Cellular floors protected/cooled

with circulating water

g

– Fire resistance: 90 to 120 min with

cooling & 60 min without cooling

• FRP prestressed concrete

– FRP always under high stress

C

ld b

iti

l it

ti

– Could be a critical situation

– 26 minutes fire resistance for thin

panels 45 mm tick

(20)

5/12/2009

FRP Structures under

Temperatures

FRP reinforced concrete

• FRP reinforced concrete

– More concrete cover required than steel?

– Often over-designed for strength

m

)

250

Steel Reinforcement

FRP RC Slabs

u

ra

l Cap

a

city

(kN.

m

100

150

200

CFRP ReinforcementGFRP Reinforcement AFRP Reinforcement Service Load

185

185 30 mm cover

30 mm cover

FRP‐RC Slabs

under Fire:

Designed for

strength

Time (min)

0

60

120

180

240 Fl

ex

u

0

50

90 97 115 185

90

90 Bisby 2003

(21)

5/12/2009

Fire Resistance of

FRP-Strengthened Concrete

(22)

5/12/2009

NRC-Queen’s-ISIS Study

V i

b

t

• Various member types:

– FRP-strengthened RC slabs

– FRP-wrapped RC columns

– FRP-strengthened RC T-beams

E

i

t l

d

i

l

• Experimental and numerical:

– Intermediate and full-scale fire tests

– Numerical thermal & structural

responses

• Goals:

– Understand fire behaviour

(23)

5/12/2009

Test specimens / FRP Wrapping / Insulation Schemes

Columns

0 mm

C

t

Circular Columns (4)

Square Column (1)

40 ALL COLUMNS

Coating

Insulation

CFRP or GFRP

Concrete

Reinforcing Steel

ALL COLUMNS:

Length = 3810 mm

End Conditions = Fixed-Fixed

f’

_c

[circular] = 40MPa

f’

_c

[rectangular] = 52MPa

(24)

5/12/2009

Fire Test Results: Columns

Column w/ 57 mm Ins.

Immediately After Failure

Column w/ 57 mm Ins.

(25)

5/12/2009

Test Results for Column with

Insulation Thickness = 57 mm

1200

ra

tu

re

(

o

C)

600

800 1000

1200

Furnace Temp.

EI/VG Interface

0

60

120

180

240

300 Te

mp

e

0

200

400 FRP Bondline

EI/VG Interface

FRP Surface

Temperatures recorded at various key locations in

Column during fire exposure

Time (min)

(26)

5/12/2009

Unprotected Column after Fire

Fire Endurance = 210 min (3.5 hrs)

C d Fi

E d

4 h

Code Fire Endurance = 4 hours

(27)

5/12/2009

Column Strengths

Insulation =

32 mm

57 mm

None

53mm

38 mm

3000

4000

5000

k

N)

Insulation = 32 mm 57 mm None 53mm 38 mm

3.5 hrs

>4 hrs

1000

2000

3000

Load (

k

Failure Load

Predicted Room Temp. Strength

0 Ci

rc

ul

ar

1 Ci

rc

ul

ar

2 Ci

rc

ula

r -

3 Ci

rc

ula

r -

4 Sq

uar

e

(28)

5/12/2009

Numerical models (columns)

Fire

Wrap

Insulation

Fire

Wrap

Column

Concrete

Column

Centreline

Schematic of

discretization for heat

transfer analysis

Schematic of

discretization for load

capacity analysis

(29)

5/12/2009

Model results - column

Column ISIS-2: Wrap Temperatures

e

(

o

C)

800 1000

EI/VG

ULC-S101

p

ULC-S101

Insulation Surf.

T

em

per

at

ur

e

200

400

600 Test Data

VG/FRP

FRP/Concrete

Model Predictions

Insulation Surf.

FRP Outside

FRP Inside

Time (min)

0

60

120

180

240

300

(30)

5/12/2009

Large-Scale T-Beams

f ll

l fl

f

• 4 tests in full‐scale floor test furnace

– CFRP for flexure

– U‐wrap GFRP anchorage

– 4 supplemental insulation schemes

• Exposed to ASTM E119 standard fire

• Subjected to sustained service

uniformly distributed load

(31)

5/12/2009

Beam-Slab Assemblies - Before

and after fire test

Beam after test and Failure

Beam before test

(32)

5/12/2009

1200

T

< GTT

Beam-Slab Assemblies –

Test Results

ure [

ºC]

800 1000 1200

‣ T

FRP-AVG

< GTT

(93°C)

for 56min

‣ T

_FRP

at 4hours:

442 °C

Furnace Temp.

FRP/C

t

T

e

m

p

erat

200 400 600

442 °C

Insulation

Surface

FRP Surface

FRP/Concrete

Interface

‣ T

_Rebar

at 4hours:

332 °C

(< 593°C)

Insulation thickness: 38mm

Time [minutes]

0 50 100 150 200 250 300 0

‣ T

Unexposed-Avg

at

4hours:

69 °C

(< 140°C)

(33)

5/12/2009

Beam Temperatures: FRP

Bondline

T

_c, steel

(34)

5/12/2009

BeamSlab Assemblies

-Heat Transfer Models

C

_L

_{• Explicit finite difference method}

C

_{• Explicit finite difference method}

• Discretize beam

• Thermal equilibrium for each element

• Accounts for variation in thermal properties

and moisture content

L

Concrete

R di ti

Conduction

Produces temperature distribution within

beam section at any time during fire

Beam Cross-Section

FRP

Radiation

(35)

5/12/2009

Beam-Slab Assemblies - Models

FRP-Concrete Bondline

[º

C]

600

800 Measured

Model Prediction

T

e

mp

erature

200

400 _{Time [minutes]}

0

60

120

180

240

300

(36)

5/12/2009

Beam-Slab Assemblies - Models

Steel Reinforcement

[ºC

]

400

500

600 Measured

Model Prediction

T

e

mper

atu

re

200

300 _{Time [minutes]}

0

60

120

180

240

300

0

100

(37)

5/12/2009

Key Findings

• FRP-strengthened and adequately-protected

concrete systems can achieve 4-hour fire ratings

• Insulation system remained robust during fire and

effectively protect FRP systems

• Numerical models have been developed to predict

FR of FRP-strengthened concrete systems

(38)

5/12/2009

Design Implications

(39)

5/12/2009

Philosophy for Fire-Safety

Temp.

(ºC)

Load

Strength

Service Load

Fire Event Onset

0 1 2 3 4

1000

100 Retrofit

Construction

Time

Initial Service Life

Retrofitted Life

(40)

5/12/2009

Conceptual design approach

trengtheningtrengthening

Protect FRP Itself

Flame spread

protection

A

mount of S

t

A

mount of S

t

Fire resistance

p

(41)

5/12/2009

Fire Design for FRP

• Base design on behaviour of member or

structure not material only

• Ensure flame spread and smoke

generation requirements are met

• Fire testing

– too expensive

• Performance based design

• Performance-based design

– best approach

(42)

5/12/2009

Performance-based fire design

• integrated testing and numerical modelling

• consider potential combustion of FRP

• incorporate external insulation

• numerical models validated against tests

• ensure external insulation stays in place

throughout fire duration (testing)

(43)

5/12/2009

Fire Safety Design Requirements

• FRP strengthened members require supplemental

insulation to resist increased service loads during fire

• FRP strength could be used in a fire situation if and only if

the temperature of the FRP is kept below a “critical”

temperature

• The nominal strength at high temperature should at all

times be greater than the strengthened service load on

members

• NB: no requirement that temperatures remain below T

_g

!

(44)

5/12/2009

*Important Note

• Fireproofing for FRP strengthening systems

is not necessarily

“one system fits all”

one system fits all

– Engineering checks are required to

determine the fire rating of the existing

t

ith

t FRP

d fi

structure with or without FRP and fire

insulation

(45)

5/12/2009

Application Cases:

Manufacturing Plant - Denver

R

f l b

• Roof slab

damaged by fire

• Repaired with 1

layer of CFRP

y

sheets

• Insulation for 1

hour fire rating

Wire mesh

– Wire mesh

– Spray applied

(46)

5/12/2009

Application Cases: Bank Building

- Vancouver

S

h

i

d d f

• Strengthening needed for

increased loads

– High-density filing system

• Repaired with 1 layer of

CFRP sheets

• Insulation for 2 hour fire

rating

– Wire mesh

Wire mesh

– Spray applied

(47)

5/12/2009

Future directions

M t i l h

t i ti

(

ti

l l “ iti

l”

• Material characteristics (particularly “critical”

temperatures for FRPs)

• Improve FRP properties at high temperatures

(e.g., increas of T

_g,

)

• Numerical and experimental studies for

near-surface mounted (NSM) reinforcement systems

• Design guidelines for all types of systems

• Detailing

g

(48)

5/12/2009

Acknowledgements

Th t

h i

l t ff f Q

’ U i

it

d th

• The technical staff of Queen’s University and the

National Research Council

• Queen’s University

• ISIS Canada

• National Research Council of Canada

• Fyfe Co. LLC

y

• BASF

(49)

5/12/2009

References

Bi b

L A

l “Fi

d

f fib

i f

d

l

fi

d

• Bisby, L.A. et al. “Fire endurance of fiber-reinforced polymer confined

concrete columns”, ACI Structural Journal, 102, 6, 2005, pp.883-891.

• Williams, B. et al. “Fire endurance of fiber-reinforced polymer

strengthened concrete T-beams”, ACI Structural Journal, 105, 1, 2008,

pp. 60-67.

• Bénichou N et al “Results of Fire Resistance Experiments on FRP

• Bénichou, N. et al. Results of Fire Resistance Experiments on

FRPStrengthened Reinforced Concrete Slabs and BeamSlab Assemblies

-Report No. 2”, Research -Report, Institute for Research in Construction,

National Research Council Canada, (234), pp. 65, 2007

• Bénichou, N. et al. “Results of Fire Resistance Experiments on

FRP-Strengthened Reinforced Concrete Columns - Report No. 2”, Research

g

p

,

Report, Institute for Research in Construction, National Research

Council Canada, (235), pp. 39, 2007

(50)

5/12/2009

Que st ions?