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Eurocode 5 design in comparison with fire resistance tests of unprotected
timber beams
Daniel Brandon Ph.D. M.Sc. B.Sc.
SP Technical Research Institute of Sweden
Introduction
Fire resistance:
The time to failure (in minutes) of a structure or structural member exposed to a standard fire
Introduction
Eurocode 5 calculations
of fire resistance:
• Reduced cross-section method
• Reduced material property method
• Advanced method
Introduction
Eurocode 5 calculations
of fire resistance:
• Reduced cross-section method
• Reduced material property method
• Advanced method
Introduction
Eurocode 5 calculations
of fire resistance:
• Reduced cross-section method
• Reduced material property method
• Advanced method
Introduction
Reduced cross-section method Reduced material property method Advanced method
Require the original material properties (at ambient temperature)
Introduction
Eurocode 5:
• Reduced cross-section method
Most used
• Reduced material property method
• Advanced method
Reduced cross-section method of EC5
Concerns:
• Thickness of the zero strength layer
• The use of increased strength properties under fire conditions
• The use of the method for fire resistances exceeding 60 minutes
Method Comparative analysis:
experimental results VS. predictions
Predictions require the original material
properties (at ambient temperature)
1. Strength grading
2. Reference tests
3. Young’s modulus
4. Density
Method Comparative analysis:
experimental results VS. predictions
Predictions require the original material
properties (at ambient temperature)
1. Strength grading
2. Reference tests
3. Young’s modulus
4. Density
Comparison 1
Comparison 2 (higher uncertainties)
Comparison 1a
12 tests with given strength class
VS.
Predictions following
Eurocode 5
As the characteristic strength is used, 95% of the predictions should be
conservative
Comparison 1b
12 tests with given strength class
VS.
Predictions using:
- The 5th instead of the 20th perc. strength
- The zero strength layer according to EC5
As the characteristic strength is used, 95% of the predictions should be conservative
Comparison 1c
12 tests with given strength class
VS.
Predictions using:
- The 5th instead of the 20th perc. strength
- Double zero strength layer in comp. with EC5
As the characteristic strength is used, 95% of the predictions should be conservative
Comparison 2
67 tests with given strength class
VS.
Predictions using:
- An estimated strength per beam
- Zero strength layer according to EC5
- Maximum fire resistance of 60 min
As the estimated strength is used, 50% of the predictions should be conservative
Comparison 2a
67 tests with given strength class
VS.
Predictions using:
- An estimated strength per beam
- Zero strength layer according to EC5
- Maximum fire resistance of 60 min
As the estimated strength is used, 50% of the predictions should be conservative
How???
Comparison 2a Estimation of the strength:
• Reference tests
• From the strength class
• From the Young’s modulus
• From the Density
Comparison 2a Estimation of the strength:
• Reference tests
• From the strength class
• From the Young’s modulus
• From the Density
Comparison 2a Estimation of the strength:
• Reference tests
• From the strength class
• From the Young’s modulus
• From the Density
Comparison 2a Estimation of the strength:
• Reference tests
• From the strength class
• From the Young’s modulus
• From the Density
Comparison 2a
0
15
30
45
60
75
90
0 15 30 45 60 75
tf;t
est
tf;calculation
10% error 20% error
Bending failure Shear/buckl. failure
Conservative Conservative
Non-
conservative
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
-60-55-50-45-40-35-30-25-20-15-10-5 0 5 10152025303540
Fre
qu
en
cy (
-)
tf;test - tf;calculation (min)
5%
normal
distribution
Comparison 2b
67 tests with given strength class
VS.
Predictions using:
- An estimated strength per beam
- Zero strength layer according to EC5
- Maximum fire resistance > 60 min
As the estimated strength is used, 50% of the predictions should be conservative
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
-40 -20 0 20 40
Fre
qu
en
cy (
-)
error: tf;test - tf;calculation (min)
normal distribution expected normal distribution
50%
Comparison 2b
0
15
30
45
60
75
90
0 15 30 45 60 75 90
tf;t
est
tf;calculation
Bending failure
Conservative
Unconservative
Conservative
Unconservative
This figure was corrected after the conference
This figure was corrected after the conference
Main conclusions • Either the strength grading or the reduced cross-section method lead
to non-conservative errors
• There is only a small number of tests for which efforts were made to determine the strength at ambient temperature
• The reduced cross-section method needs further testing to be considered for fire resistances more than 60 minutes