Upload
anuj-ramdas
View
1.215
Download
2
Tags:
Embed Size (px)
DESCRIPTION
Presentation for Tutorial Website - Brief Information on Eurocode 3 - Fire
Citation preview
Department ofCivil and Structural Engineering
HEAT TRANSFER TO EXTERNAL STEELWORK
Eurocode 3BS EN 1993 Part 1-2:2005 General rules – Structural fire design
Design of Steel Structures
Content of BS EN 1993-1-2CO
NTE
NT
Heat transfer to structural elementsH
EAT
TRAN
SFER
Column not engulfed in flame Column engulfed in flame
Beam not engulfed in flame Beam fully or partially engulfed in flame
AssumptionsAS
SUM
PTIO
NS
The size of fire compartment is considered to be single storey.
All openings in the fire compartment are assumed to be rectangular.
Determination of parameters such as compartment fire temperature, size and temperature of flames projecting out of the window, convection and radiation characteristics as per Annex B in EN 1991-1-2.
Elements distinguished as member engulfed or not engulfed in flame depending on the relative position with respect to the openings
Radiative heat transfer for an element which is not engulfed with flame projecting out from the windows.
Convective heat transfer when element is engulfed with flame and also heat transfer by radiation of flame engulfing it and also from compartment opening.
Heat BalanceH
EAT
BALA
NCE
Member not engulfed in flame
Average steel temperature Tm [K] is found by iterative solution of the
σ Tm4 + α Tm = Iz + If + 293α
Where,σ Stefan Boltzmann constant taken as 56.7x10-12 kW/m2K4
α Coefficient for heat transfer by convection [kW/m2K]Iz Heat flux by radiation from the flames [kW/m2]
If Heat flux by radiation from the opening [kW/m2]
Heat BalanceH
EAT
BALA
NCE
Member engulfed in flame
Average steel temperature Tm [K] is found by iterative solution of
σ Tm4 + α Tm = Iz + If + α Tz
Where,Tz Temperature of flame [K]
Iz Heat flux by radiation from the flames [kW/m2]
If Heat flux by radiation from the opening [kW/m2]
Heat balanceH
EAT
BALA
NCE
Relative heat flux Iz
Calculated depending on the type of member and situation as below.
Column not engulfed in flameBeam not engulfed in flameColumn engulfed in flameBeam fully or partially engulfed in flame
Heat transferH
EAT
TRAN
SFER
If = ϕf εf (1- az) σ Tf4
Where,Φf Overall configuration factor for heat transfer by radiation from
the opening for that memberεf Opening emissivityaz Flame absorptivityTf Fire temperature [K]
Opening Emissivity εf must be taken as 1.
Flame absorptivity az is calculated depending on the type of the
member and the situation.
Radiative heat flux If
Configuration factorsCO
NFI
GU
RATI
ON
FAC
TORS
To find temperatures of external members, all radiating surfaces are assumed to be rectangular in shape.
A rectangular envelope is drawn outer to the member cross-section receiving the heat transferred by radiation
The ϕ value must be determined at the midpoint P at each and every face.
P
P
P P
P
P
P
Envelope
Configuration factorsCO
NFI
GU
RATI
ON
FAC
TORS
X
a
bP
X
a
1
4 3
2 Keya) Radiating surfaceb) Receiving surface ϕ = ϕ + ϕ + ϕ + ϕ
1 2 3 4
S
a = h/s;b = w/ss distance between P and Xh Radiating surface zone
heightw zone width
1. Receiving surface in a plane parallel to the radiating surface
Configuration factorsCO
NFI
GU
RATI
ON
FAC
TORS
2. Receiving surface in a plane perpendicular to radiating surface
Configuration factorsCO
NFI
GU
RATI
ON
FAC
TORS
3. Receiving surface in a plane at an angle θ to the
radiating surface
X
1
2
P
X
a
1
2
Key1) Radiating surface2) Receiving surface ϕ = ϕ + ϕ
1 2
S
w
h
θ
Overall configuration factorsO
VERA
LL C
ON
FIG
URA
TIO
N F
ACTO
RS Overall configuration factor for an opening
di cross section dimension of member face i
Ci Coefficient for protection for member with face i
Ci = 0 for a protected face
Ci = 1 for an unprotected face
Configuration factor ϕf,i for a member with face i must be taken zero
when the opening is not visible.
Overall configuration factorsO
VERA
LL C
ON
FIG
URA
TIO
N F
ACTO
RS Overall configuration factor for flame
Configuration factor becomes zero when the flame is not visible to the member face taken into consideration.
Heat screen can be used to protect the member face. When a member face is immediately near to wall of the compartment, then it is considered as protected when there is no gap in that part of wall. Rest of the member faces are considered to be unprotected.
Member face numberingM
embe
r fac
e nu
mbe
ring
Column
Beam
Column
1
2
34
1 and 2 are perpendicular to radiator3 and 4 are parallel to radiator4 out of sight to radiator
Envelope
Beam2
1
43
Envelope
Column face numbering - Plan Beam face numbering - Section
Member dimensions - ColumnM
embe
r dim
ensi
ons
- Co
lum
n
Column opposite opening
Column
d
d2
1
(2)
(3)
s
Column
d
d 2
1
(4)
(3)
s
Column between opening
Member dimensions - BeamM
embe
r dim
ensi
ons
- Be
am
Beam parallel to wall
Beam perpendicular to wall
Beam
d
d 2
1
(3)
(4)
s
Beam
d
d 2
1
(3)
(4)(2)
Colu
mn
not e
ngul
fed
in fl
ame
Column not engulfed in flame
Column not engulfed in flame
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column opposite opening
Openings
Flames
No forced Draught: Column placed opposite an opening
Openings
Flames
Forced Draught: Column placed opposite an opening
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column opposite opening
Heat flux due to radiation when the column is placed opposite to a window opening
Iz = ϕz εz σ Tz4
Where,ϕz Overall configuration factor for flame heat of columnεz Flame emissivityTz Temperature of flame [K]
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column opposite opening
No forced draught: Wall above and h < 1.25w
Column
z
2h/3
Equivalent front rectangle 2h/3
Column
Section Plan
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column opposite opening
No forced draught: Wall above and h > 1.25w or no wall above
Column
z
2h/3
Equivalent front rectangle 2h/3
Column
Section Plan
x
x
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column opposite opening
Forced draught
Column
z
xEquivalent front
rectanglex
Column
h
w +
0.4
x
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column between opening
No forced Draught: Column placed opposite an opening
Forced Draught: Column placed opposite an opening
n openingsm openings
Flame side m Flame side n
n openingsm openings
Flame side m Flame side n
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column between opening
Heat flux due to radiation when the column is placed between window openings
Iz = (ϕz,m εz,m + ϕz,n εz,n) σ Tz4
Where,ϕz,m Overall configuration factor for flame heat of column on side mϕz,n Overall configuration factor for flame heat of column on side nεz,m Total flame emissivity on side mεz,m Total flame emissivity on side n
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column between opening
No forced draught: Wall above and h < 1.25w
Column
z
2h/3
Equivalent side rectangle 2h/3
Column
Section Plan
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column between opening
No forced draught: Wall above and h > 1.25w or no wall above
Column
z
2h/3
Equivalent side rectangle
Section Plan
x
2h/3
Column
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Radiative heat transfer - Column between opening
Forced draught
Column
x
Equivalent side rectangle
x
Column
Section Plan
h
w +
0.4
s
s
s
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e Flame Emissivity - Column opposite an opening
Emissivity of flame εz when a column is placed opposite an opening is given by using the flame thickness λ at the top of opening. In case when there is no balcony or awning, flame thickness is given as
‘No forced draught’ λ = 2h/3‘forced draught’ λ = x but λ hx/z
h, x and z are taken as per Annex B of EN 1991-1-2
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e Flame Emissivity - Column between two openings
Total emissivities εz,m and εz,n when a column is placed between two openings is given by using the flame thickness λ as follows
For side m:
For side n:
Where, m number of openings on side mn number of openings on side nλi flame thickness for opening i, which is taken as equal to the
width of the opening or window, wi in ‘no forced draught’ condition.
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e Flame thickness
‘No forced draught’ λ = wi
‘forced draught’ λ = wi + 0.4s
Where, wi Opening widths horizontal distance taken perpendicular from wall of the compartment to the centreline of the column
Column not engulfed in flameCo
lum
n no
t eng
ulfe
d in
flam
e
Temperature of flame, Tz
‘No forced draught’ l = h/2
‘Forced draught’ l = 0 column opposite an openingl = sX/x column between openings, where l is
distance on the flame axis to distance s measured from the wall of compartment.
Flame absorptivity, az
‘No forced draught’ - taken as zero.
‘Forced draught’ - equal to the emissivity of flame εz.
Beam
not
eng
ulfe
d in
flam
e
Beam not engulfed in flame
Beam not engulfed in flame
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Heat transfer by radiation
Bottom of beam does not go below the top level of the opening
The two ways of beam orientation with respect to the external - Beam parallel to compartment wall- Beam perpendicular to compartment wall
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Average steel temperature, Tm – Beam parallel to wall
Is calculated at a point on the beam directly above the centre of the opening.
Iz = ϕz εz σ Tz4
Where, ϕz Overall configuration factor of flame opposite to the beamεz Emissivity of flameTz Temperature of flame
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Average steel temperature, Tm – Beam perpendicular to wall
Is calculated at every 100mm distance along the length of the beam.
Iz = (ϕz,m εz,m + ϕz,n εz,n ) σ Tz4
Where,ϕz,m Overall configuration factor of beam heated by flames on side mϕz,n Overall configuration factor of beam heated by flames on side nεz,m Emissivity of flames on side mεz,n Emissivity of flames on side nTz Temperature of flame
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Emissivity of flame, εz - Beam parallel to wall
In case when there is no balcony or awning, flame thickness is given as
‘No forced draught’ λ = 2h/3‘Forced draught’ λ = x but λ hx/z
h, x and z are taken as per Annex B of EN1991-1-2
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Emissivity of flame, εz,m and εz,n - Beam perpendicular to wall
For side m:
For side n:
Where, m number of openings on side mn number of openings on side nλi opening width
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Flame thickness - λi
‘No forced draught’ λi = wi
‘Forced draught’ λi = wi + 0.4s
Where, wi Opening widths horizontal distance taken to the point on beam from wall of the
compartment
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Beam not engulfed in flame
z
2h/3
Equivalent front rectangle
2h/3
Section Plan
Equivalent side rectangle
Beam
Beam
Equivalent front rectangle
No forced draught: Wall above and h<1.25w
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Beam not engulfed in flame
No forced draught: Wall above and h>1.25w or no wall above
z
2h/3
Equivalent front rectangle
2h/3
Section Plan
Equivalent side rectangle
Beam
Beam
Equivalent front rectangle
x
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Beam not engulfed in flame
Forced draught
h
Equivalent front rectangle
s
Section Plan
Equivalent side rectangle
Beam
Beam
Equivalent front rectangle
x
z
x
w +
0.4
s
Beam not engulfed in flameBe
am n
ot e
ngul
fed
in fl
ame
Flame temperature, Tz
‘No forced draught’ l = h/2
‘Forced draught’ l = 0 beam parallel to external wall on top of opening
l = sX/x beam perpendicular to external wall with no awning on top of opening, where l is distance along the flame axis to distance s measured from the wall of compartment.
Flame absorptivity, az
‘No forced draught’ - is taken as zero.
‘Forced draught’ - equal to the emissivity of flame εz.
Colu
mn
engu
lfed
in fl
ame
Column engulfed in flame
Column engulfed in flame
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Radiative heat flux Iz
with,Iz,1 = C1 εz,1 σ Tz
4
Iz,2 = C2 εz,2 σ Tz4
Iz,3 = C3εz,3 σ To4
Iz,4 = C4 εz,4 σ Tz4
where, Iz,i Heat flux due to radiation on column due to flameεz,1 Flame emissivity with respect to face i of the columni indicator for column faceCi Coefficient of protection for face iTz Temperature of flameTo Temperature of flame at opening
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Column engulfed in flame
Forced draught
Column
λ
FlameColumn
Section
d λ4 31
Plan
λ d λ4 31
Flame
λ1
λ2
d2
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Column engulfed in flame
No forced draught condition
Column
λ
FlameColumn
Section
d λ4 31
Plan
λ
d λ
4
31
Flame
λ1
λ2
d2 FlameAxis
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Column engulfed in flame
Forced draught: Flame axis intersects column axis above top of opening
Column
λ
FlameColumn
Section
d λ4 31
Plan
λ
d λ
4
31
Flame
λ1
λ2
d2 FlameAxis
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Column engulfed in flame
Forced draught: Flame axis intersects column axis above top of opening
Column
λ
FlameColumn
Section
d λ4 31
Plan
λ
d λ
4
31
Flame
λ1
λ2
d2 FlameAxis
Column engulfed in flameCo
lum
n en
gulfe
d in
flam
e
Emissivity of flames εz,i for each face of column is found from ε stated in Annex B, EN 1991-1-2, replacing flame thickness λ with dimension λi
Temperature of flame Tz
No forced draught’ l = h/2
Forced draught’ l = (λ3 + 0.5 d1) X/x but l 0.5hX/z, where l is
distance along the flame axis to the level where λ1 is measured with
condition that there is no balcony or awning above the opening.
Flame absorptivity az
Where εz,1 , εz,2 and εz,3 are the emissivities of flame for column faces 1, 2 and 3.
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
e
Beam fully or partially engulfed in flame
Beam fully or partially engulfed in flame
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Radiative Heat Transfer
AssumptionsBeams bottom not going below the top level of the adjoining opening
There are two separate cases, - Beam parallel to the fire compartment wall - Beam perpendicular to the fire compartment wall
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Beam engulfed in flame – No forced draught
λ
Flame
Section
d λ3 41
Elevation
λ d λ3 41
λ
λ
d
1
2
2
Opening
Compartment wall
Beam perpendicular to wall Beam parallel to wall
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Beam engulfed in flame – No forced draught
Top of flame below top of beam Beam immediately adjacent to wall
Flame
Section
λ d3 1
λ
λ
d
1
2
2
Flame
Section
λ d λ3 41
h
λ
d
1
2 z
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Beam engulfed in flame – Forced draught
Beam not adjacent to wall Beam immediately adjacent to wall
Flame
Section
λ d3 1
λ
λ
d
1
2
2
Upper surface of
flame
Flame
Section
λ d3 1
d2λ
1
λ4
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
The average temperature Tm Found at a point along the length of beam just above the midpoint of opening when the beam is parallel to the external wall.
In the case of beam perpendicular to the external wall is found by taking maximum of calculated values at every 100mm along the length of beam.
Heat flux due to radiation Iz due to flame is found by
with, Iz,i heat flux due to radiation Iz from flame to beam face ii Indicator for face of beam
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
The average temperature Tm Found at a point along the length of beam just above the midpoint of opening when the beam is parallel to the external wall.
In the case of beam perpendicular to the external wall is found by taking maximum of calculated values at every 100mm along the length of beam.
Heat flux due to radiation Iz due to flame is found by
with, Iz,i heat flux due to radiation Iz from flame to beam face ii Indicator for face of beam
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
No forced draught
- Flame above the top of the beam and when the flame is below the top of beam.
Following equations are used when top of flame is over the upper part of beam
Iz,1 = C1 εz,1 σ To4
Iz,2 = C2 εz,2 σ Tz,24
Iz,3 = C3 εz,3 σ (Tz,14 + Tz,2
4)/2Iz,4 = C4 εz,4 σ (Tz,1
4 + Tz,24)/2
where, εz,i emissivity of flame for face i of the beamTo Temperature at openingTz,1 Temperature of flame at bottom level of beamTz,2 Temperature of flame at top level of beam
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
No forced draught
In case the beam is parallel and directly adjoining the compartment wall, C4 is taken equal to zero.
In case top of flame reaches only below the beam top,
Iz,1 = C1 εz,1 σ To4
Iz,2 = 0Iz,3 = (hz/d2) C3 εz,3 σ (Tz,1
4 + Tx4)/2
Iz,4 = (hz/d2) C4 εz,4 σ (Tz,14 + Tx
4)/2
where, Tx Temperature of flame at tip [813 K].hz Height of the flame top measure from beam bottom.
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Forced draught
In the case of forced draught condition- Beams placed directly adjoining to the external wall, or - Beam placed not directly adjoining to the external wall
When the beam is placed parallel to the wall and away from the wall or even when the beam is perpendicular to the wall following equations are used
Iz,1 = C1 εz,1 σ To4
Iz,2 = C2 εz,2 σ Tz,24
Iz,3 = C3 εz,3 σ (Tz,14 + Tz,2
4)/2Iz,4 = C4 εz,4 σ (Tz,1
4 + Tz,24)/2
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Forced draught
If a beam is positioned parallel and directly adjoining to the compartment wall, the bottom face is considered engulfed in flame, while on one side and top of beam is only exposed to radiative heat transfer from the upper portion of the frame.
Iz,1 = C1 εz,1 σ To4
Iz,2 = ϕz,2 C2 εz,2 σ Tz,24
Iz,3 = ϕz,3 C3 εz,3 σ (Tz,14 + Tz,2
4)/2Iz,4 = 0
Where ϕz,i configuration factor relative to the upper portion of the flame, for face i of the beam, from Annex G in EN 1991-1-2.
Beam
fully
or p
artia
lly e
ngul
fed
in
flam
eBeam fully or partially engulfed in flame
Emissivity of flame εz,i
Flame emissivity εz,i for each face of beam if found using the formula stated in Annex B of 1991-1-2, using flame thickness λi corresponding to each face of thebeam.
Flame Absorptivity
Absorptivity of flame az is found by using the expression
az = 1 – e-0.3h
The End