10 fire protection design (2)

7/24/2019 10 Fire Protection Design (2)

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10 Passive Fire Protection to

Steel Beams and columns

Professor Richard Liew

Department of Civil & Environmental Engineering

National University of Singapore



Why protect from fire ?

All commonly used building materialslose some strength when exposed to

fire

Concrete - spalls to expose reinforcement

Wood - depletes by charring

Steel - loses design margin of safety around

550°C.



The Result



Structural Fire Protection – The Options

1. Active

•Sprinklers•Water Sprays

•Deluge Systems

2. Passive

Construction materials or coatings which limit the

temperature rise of a steel structure in the event of a

fire



Types of Passive Fire Protections

1 Concrete 2.Spray Vermiculite 3. Fire insulation Board

4.Intumescents paint



6

Composite beams with fire protection



Sprayed Vermiculite Protection

Vermiculite or sprayed mineral fibre



Fire Insulation Board



Intumescent coatings

“reactive”, swelling to

many times their originalthickness when exposed to

fire., with the resultant char

insulating the steel

Up to 120 mins fire resistance time for thin

film intumescent coatings

Up to 240 mins fire resistance time for thick

film intumescent coatings (epoxy coatings)



Intumescent Coating



Fire Code

Occupancy Type

Requirement for fire rating

Section Factor A / V

A: expose sect.

surface

V: volume of steelsect.

Manufacturer’s Design Manual

Thickness for Fire Protection

Fire resistance design : design process of prescriptive approach



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Section factor

Section factor = Hp / A (in m-1)Hp is the heated perimeter (in m);

A is the gross cross-sectional area of the section (in m2).

The section factor is thus a measure of the rate at which a

section will heat up in a fire. The higher its value, the greaterwill be the protection thickness is required.



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Section factor

A steel section with a large perimeter (Hp) will receive moreheat than one with a smaller perimeter.

The greater the cross sectional area (A) of the section, the

greater is the heat sink. The lower the steel temperature.

Hp1 > Hp2

A1 < A2

TDesign1 > TDesign2



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Section factor (m-1)- I sections and H sections

Typical range:

60 ~ 300



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Section factor (m-1)- Hollow sections

Typical range:

60 ~ 300



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Design of Passive fire protection

Sprayed fire protection- Wet site operation, economical but lack control in thickness.

Board fire protection- dry site operation, better control on material and installation.

Intumescent paint fire protection- shop operation, expensive but good control on material and

application of paint.



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Sprayed fire protection- CAFCOTE 280



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19

Board fire protection- VICUCLAD



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21

Intumescent fire protection- NULLIFIRE SYSTEM S



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Intumescent paint fire protection- NULLIFIRE SYSTEM S



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Example : A steel beam under fire- with concrete topping and fire protection

DD = 19 kN/m LL = 9 kN/m

Section: UB 457 x 152 x 52

Steel grade 355

Span = 8 m

Assume enough lateral restraints are provided to avoid lateral torsional buckling.

Applied load:

Live load: 9 kN/m

Dead load: 19 kN/m

FRP = 1 hr

8 m



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Design procedure

Section factor = Hp / A

= (3B+2D-2t) / A

= (3 x 152.4 + 2 x 449.8 – 2x 7.6) / 6620

= 1341.6 / 6620 mm -1

= 202.6 m-1

Selected required thickness of fire protection

material.

FRP = 1 hr



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26




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Intumescent paint fire protection- NULLIFIRE SYSTEM S



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Summary

Type of fire

protection

Sprayed fire

protection

Board fire

protection

Intumescent paint

fire protectionThickness of

fire protection

(mm)

16 16 – 18 1.0

UB 457 x 152 x 52 FRP = 1 hr



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Example 2 A steel column with fire protection

50 kNm

50 kNm

750 kNSection: UC 203x203x46

Steel grade 355

System height = 3 m

Applied load:

Axial load: 750 kN

Bending moment: 50 kNm

FRP = 1 hr



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Design procedure

Section factor = Hp / A

= (4B+2D-2t) / A

= (4 x 203.2 + 2 x 203.2 – 2 x 7.3) / 5880

= 1611 / 5880 mm-1

= 273.9 m-1

Selected required thickness of f ire protectionmaterial.

FRP = 1 hr

St l l t t d b t



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Steel column protected by concrete

encasement

Minimum concrete cover, c = 50 mm

(mins)

EC4 – Part 1: 1-2



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Summary

Type of fire

protection

Concrete

cover

Sprayed fire

protection

Board fire

protection

Intumescent

fire

protection

Thickness offire protection

(mm)

50 18 16 – 18 1.23

UC 203 x 203 x 46 FRP = 1 hr



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Comments on passive fire protection Passive fire protections aim to provide insulation of the

structural members under the standard fire exposes; i.e.

to keep the temperature down

No information on the final temperature and deflection ofthe structural members

Any crack in the passive fire protection system?

Any detachment of the passive fire protection systemdue to member deformation during heating i.e.

“stickability”?

Same thickness of passive fire protection system isapplied to all members irrespective of the memberlengths or the load ratios, hence, this approach is very

conservative.



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Composite beam Eurocode 4: Part 1.2 (2005)



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Composite beamwith partial concrete encasement (ηfi, t< 0.5)

ηfi, t is the load ratio.

= Rfi, t / Rd

Table 4.1

b= minimum width of concrete encasement

Min b

As / Af

Table 4.2: Minimum axis distance for additional reinforcement of composite beams.



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Composite beamwith partial concrete encasement (minimum cover)

Table 4.2 Minimum axis distance for additional reinforcement of composite beams

b

u 1u2

Standard Fire

Resistance

Min. Axis

Distance

[mm]

Profile

Width

b [mm]

> 300

250

200

170 u 1

u 2

u 2

u 2

u 1

u 1

u 1

u 2

100 120 - -

--6045

35

40

(25)

50

50

45

60

70

60

80 100 120 -

40 55 60 -

60 75 90 12060

90

60

R180R120R90R60

_



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Composite beamwith ful l concrete encasement

Table 4.3

Standard Fire

Resistance

R30 R60 R90 R120 R180 Concrete cover c [mm] 0 25 30 40 50

Concrete

for Insulation

Slab

c

c



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Design procedure for composite beams

Evaluate the load ratio.

Select the minimum amount of steel reinforcement

according to required FRP.

Select the required concrete cover to steel

reinforcement.



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Load ratio in fire

Relative to ambient-temperature

design resistance

d

t .d . fi

fi R

E =η

Either …..

Relative to ambient-temperature

design load (more conservative) Or more

usefully…..

d

t .d . fi

fi E

E =η

1.k 1.Qk G

1.k 1.1k GA fi

QG

QG

γ γ

ψ γ η

+

+=



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EC3 partial safety factors

In Fire limit state

γ GA = 1,0 Permanent loads; accidental design situationsψ 1.1 = 0,5 Combination factor; variable loads, offices

Ambient temperature strength design

γ G = 1,35 Permanent loads;

γ Q.1 = 1,5 Combination factor; variable loads

Qk.1 /Gk 1 2 3 4

η fi 0,53 0,46 0,43 0,41

1.k 1.Qk G

1.k 1.1k GA fi

QG

QG

γ γ

ψ γ η

+

+=



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Example 2: A composite beam with partial concrete

encasement

Concrete section: 1000 x 125 mm

Steel section: UB 457 x 152 x 52

Steel grade 355

Span = 8 m

FRP = 1 hr

Load ratio, ηfi,, t = 0.5

75

457

50

152 × 10.9

152 × 10.9

7.65

1000

Y10

As u1 u2



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Composite beamwith partial concrete encasement (ηfi, t< 0.5)

h=449.8 b=152.4, min b = 100, As/Af =0

As / Af As / Af As / Af As / Af As / Af



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Composite beamwith partial concrete encasement (minimum cover)

Example 6



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Composite beamwith partial concrete encasement

u1 = 100 mm

u2 = 45 mm

From the table in s lide 79

Min b = 100 mm

Actual b = 152 mm ok

As = 0 x Af mm2

75

457

50

152 × 10.9

152 × 10.9

7.65

1000

Y10

As

u1

u2

Design summary

Provide nominal reinforcement



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Composite Column Eurocode 4: Part 1.2 (2005)



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Composite column sectionsbc

cy cy b

d

cz

cz

dc tw

t f

bc

b

dc

tf

tw

dc tw

tf

b= bc

y

z

b

d

t

y

z

t

d

y

z

t

d



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Steel column with full concrete encasement



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Design procedure for composite column

Evaluate the load ratio.

Select the minimum amount of steel reinforcement

according to required FRP.

Select the minimum cross-sectional conf iguration

and concrete cover to steel reinforcement.



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Composite Column- concrete filled hollow sections (ηfi, t< 0.28)


= Rfi, t / Rd

Table 4.7



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Composite Column- concrete filled hollow sections (ηfi, t< 0.47)

ηfi,, t is the load ratio.

= Rfi, t / Rd

Table 4.7



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Composite Column- Concrete filled hollow sections (ηfi, t< 0.66)


= Rfi, t / Rd

Table 4.7



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Example 7: A concrete filled hollow section

FRP = 1 hr

Load ratio, ηfi,, t = 0.5

550

All dimensions are in mm.

550

us

As

Ac

Need to determine As and

concrete cover for 1 hr FRP



53

Composite Column

- Concrete fil led hollow sections (ηfi, t< 0.66)



54

Composite Column- Concrete fil led hollow sections

Minimum ratio of reinforcement:

As / (As + Ac) = 0.06

As = 550 x 550 x 0.06

= 18150 mm2

us = 30 mm

5 5 0

550

us

As

Ac



Overall comments

Limiting temperature method is of very limiteduse and fire protection is often needed.

Passive fire protection system is simple to use

but conservative with limited control on thermaland structural behaviour of structural members.

10 fire protection design (2)

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