02 november 2015 1 en 1992-1-2: structural fire design ec2 workshop eurocodes moscow 2010 j.c....
TRANSCRIPT
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EN 1992-1-2: Structural fire design
EC2 Workshop Eurocodes Moscow 2010
J.C. Walraven
Vermelding onderdeel organisatie
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Information on structural fire design - Eurocode 1: EN 1991-1-2, : Loads on structures, Part 1-2: General loads – Loads due to fire
- Eurocode 2: EN 1992-1-1: : Design and calculation of concrete structures: General rules and rules for buildings
- Eurocode 2: EN 1992-1-2:
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Control of structures subject to fire Eurocode distinghuises analysis of elements, partial
systems andstructures as a whole
Analysis of structural member
Analysis of structural system
For the design of standard fire requirements in general the analysis of structural members is sufficient.
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Alternative design procedures EC2
Prescriptive Rules
Member analysis Analysis of part of structure
Analysis of entire structure
Calculation of mechanical
actions at boundaries
Tabulated data
Simple calculation
models
Advanced calculation
models
Simple calculation
models
Advanced calculation
models
Advanced calculation
models
Calculation of mechanical actions at boundaries
Selection of mechanical
models
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Alternative design procedures Performance based design;
physically based thermal actions
Selection of simple or more advanced fire development models
Member analysis
Analysis of part of the structure
Analysis of entire structure
Calculation of mechanical
actions at boundaries
Calculation of mechanical
actions at boundaries
Selection of mechanical
models
Simple calculation
models
Advanced calculation
models
Advanced calculation
models
Advanced calculation
models
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Summary table for alternative methods
Tabulated data
Simplified calculation methods
Advanced calcu- lation methods
Member analysisMember considered to be isolated. Indirect fire actions are not considered, except those resulting from thermal gradients
Yes- Data given for standard fire only, 5.1(1).- In principle data could be developed for other curves
Yes-Standard fire and parametric fire, 4.2.1(1)
- Temperature profiles given for standard fire only, 4.2.2(1)- material models apply only to heating rates similar to standard fire 4.2.4.1(2)
Yes4.3.1(1)Only principles are given
Analysis of parts of the structureAnalysis of the entire structure. Indirect fire actions within the subassembly are considered, but no time dependant interaction with other parts of the structure
No Yes-Standard fire and parametric fire 4.2.1(1)-temperature profiles given for standard fire only 4.2.2(1)- material models only for heating rates similar to standard fire 4.2.4.1(2)
Yes4.3.1(1)POnly the principles are given
Global structural analysisAnalysis of entire structure. Indirect fire actions considered throughout structure
No No Yes4.3.1(1)POnly principles are given
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Alternative design procedures
Prescriptive rules (traditional):
Rules for minimum cross sections, minimum cover, reinforcement geometry, mostly based on ISO 834 curve
Performance based design (modern/future))
Bearing capacity should be maintained during fire (Criterion R) In case of subdivision of building in compartments: separating elements (including joints) should keep their separating function during the fire, so: - no loss of integrity due to cracks, wholes which would allow transmission of gas or flames (Criterion E) - no loss of isolating function which would lead to rise of temperature at opposite side resulting in fire (Criterion I). Mostly assumed to be satisfied if max. T < 180 K.
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Modeling the fire load
For general (standard cases) ISO 834 curve is appropriate
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More advanced heating curves (for performance based design)
Parameters• Burning capacity of materials
in room• Opening-factor• Wall-, floor and ceiling
properties• Risk factors (presence of
sprinklers or alarm system)• Ventilating conditions
Parametric temperature – time curves
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Load on the structure during fire
Accidental loading situation applies:
for buildings: 0,5 x,1 0,9 and 0,3 x,2 0,8
Accidental action Ad due to imposed deformations as a result of thermal actions in statically indeteminate structures
1
,211,1 i
kiikxdj
kkj QQAPG
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Special case of imposed deformations
1
,211,1 i
kiikxdj
kkj QQAPG
Accidental load due to restrained temperature deformations
Dotted lines: shifted moment lines due to temperature restraint!
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Basis for control of fire resistancce
Rd bearing resistance (no fire)Ed design load (no fire)
Rfi,d(t) bearing resistance (fire)Ed = fiRd governing load for fire
situationtfi,req required fire resistance in minutes (criterion R)
Rfi,d(t) can be calculated on the basis of material laws which reflect material deterioration under increasing temperature
)()( ,, tRtE fidfid
for tfi,req
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Control with tables - Based on ISO temperature – time curve- Provides design solutions for standard fire exposure up to 4
hours- Valid for normal weight concrete with siliceous aggregate- For calcareous or lightweight aggregates the minimum
dimension may be reduced by 10%- No further checks required for shear, torsion or anchorage- No further checks required for spalling up to an axis distance
of 70mm- For HSC (> C50/60) the minimum cross section dimension
should be increased- Axis distance a according to figure (nominal
values- The tables have been derived for a critical rein-
forcing steel temperature of 5000C and a loadingdegree of fi = Ed,fi/Ed
a AxisDistance
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a AxisDistance
Example of a table: Minimum thickness and axis distance for flat slabs
Control with tables
Standard fire resistance
Minimum slab thick-ness (mm)
Minimum axis dis-tance (mm)
R 30 150 10
R 60 180 15
R 90 200 25
R 120 200 35
R 180 200 45
R 240 200 50
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Control with tables
Combination with diagrams
In combination with the tables diagramscan be used, which give the reduction ofthe steel strength as a function of the increasing temperature. These relationscan be used to convert the results of the tables to degrees of loading differentfrom 0,7 and critical temperaturesother than 5000 C
0,8
1
0
1
2
3
0,6
0,2
0,4
1000200 800400 12000 600
ks(cr), kp(cr)
cr [°C]
Prestressing strands and wires
Reinforcing steel
Prestressing bars
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Control with tables
provs
reqs
s
yk
d
fidfis S
ACf
E
E
,
,0
,,
)20(
The tables have been derived for a critical steel temperature cr = 5000, a loading degree fi = 0,7, and s =
1,15.The corresponding steel stress is
for Ed,fi/Ed = 0,7; s = 1,15 and As,req/As,prov
= 1 a stress s=300 MPa is found, so s/fyk=0,6. This is confirmed by the
diagram
0,8
1
0
1
2
3
0,6
0,2
0,4
1000200 800400 12000 600
ks(cr), kp(cr)
cr [°C]
yks f/
Temp.
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Control with tables
Procedure for combined use of tables and diagrams
Example: Qk=Gk and fi = 0,7. With G=1,35
and Q=1,5 it is found that fi = Efi,d/Ed = (1/1,35 +
0,7/1,5)/(1+1)=0,6If As,req/Asprov = 0,9, then the stress in the
rein-forcing steel under fire conditions is:s = fi{fyk(200)/s}(As,req/As,req) =0,6(500/1,15)0,9 = 235 MPa. So
=235/500 = 0,47. From the diagram (andcorresponding mathematical relations) it
is readthat the critical temperature is cr = 556
MPa.So the axis distance (Tabulated value)
can bereduced by:
a = 0,1(500-556) = - 5,6 mm
0,8
1
0
1
2
3
0,6
0,2
0,4
1000200 800400 12000 600
ks(cr), kp(cr)
cr [°C]
yks f/
Temp.
yks f/
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Control with tables
NRd = Asfyd + Acfcd
= Asfyk+Acccfck/c
Rd
Edfi
Rd
fiEd
N
N
N
Nn
,
Example of table: dimensions for columns
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Design with tables
Standard fire resistance
Slab thickness(mm)
One direction
2 directionsly/lx 1,5
2 directions1,5 < ly/lx 2
R30 60 a = 10 mm a= 10 a= 10
R60 80 a = 20mm a= 10 a= 15
R90 100 a= 30 mm a= 15 a= 20
R120 120 a= 40 mm a= 20 a= 25
R180 150 a= 55 mm a= 30 a= 40
R240 175 a= 65 mm a= 40 a= 50
Minimum slab thickness and axis distance a for slabs spanning in one and 2 directions
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bfi
b
dfi
50500 °C
d
C
T
dfid
bfi
b
500 °C
500°C isotherm method (Annex B1)(Anderberg)
• Determine the position of the 500C isotherm for the specific fire exposure.
• Determine the values of dfi and bfi.
• Determine the temperature and reduced strength of reinforcing bars in the tension and compression zones.
As
As'
z' dfi
bfi
z
fcd,fi(20)
xbfifcd,fi(20)
As1fsd,fi(m)
z'
Fs = As2fsd,fi(m)
Fs = As'fscd,fi(m)
Mu2Mu1
xx
+
• Use conventional calculation method to determine ultimate load capacity.
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M1 aZ2
w2
M2
w1
aZ1
aZ1
Zone method (Annex B2)(Hertz)
• Section is divided into zones. The mean temperature and mean compressive strength, fcd( ) of each zone is determined
• The fire situation is represented by a reduced cross section ignoring a damaged zone of thickness az.
• The value of az is determined by assessing the mean properties of the concrete at point M
• The example shows the combination of two sets of calculations. One for the flange and one for the web.
kc( M)
kc()
kc( )
kc( 2)
kc( 3)
w w
kc( 3)
M
• The point M is an arbitrary point selected on the centre-line of the section
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Mfi = f(1/r) (N = NEd,fi)
M2,fi
M0Rd,fi
M
1/r
MRd,fi
M2,fi = NEd,fi (1/r) l0 /c2
• Divide cross-section into zones with mean temperature of 20C, 100C, 200C, 300C ... up to 1100C.
Buckling effects on columns (Annex B3)(Isquierdo)
Ac,i,j
yi,j
xi,j sup
i,j
s1
s2
s3
inf
• Determine temperature of each reinforcing bar.
• Determine ultimate moment capacity, MRd,fi for NEd,fi and nominal second order moment, M2,fi for corresponding curvature.
• Integrate to determine moment-curvature diagram for each zone and reinforcing bar for NEd,fi
• Determine ultimate first order moment capacity, M0Rd,fi and compare with M0Ed,fi
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Fire in praxis
Fire in Faculty of Architecture, Delft
University of Technology
13 May 2008, 10h30
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TU Delft, Faculty of Architecture, May 13th 2008, 13h00
Fire in praxis
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TU Delft, Faculty of Architecture, May 13th
2008 16h00
Fire in praxis
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TU Delft, Faculty of Architecture, May 13th
2008 17h00
Fire in praxis
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TU Delft, Faculty of Architecture, May 13th
2008 19h00
Fire in praxis