eurocode 5 design in comparison with timber beams · eurocode 5 as the characteristic strength is...
TRANSCRIPT
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
Timber in fire:
• Chars
• Contains moisture
• Has low thermal
• conductivity
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
Reduced Cross Section Method of EC5 Adaptation of the 5th percentile strength
Reduced Cross Section Method of EC5 Adaptation of the 5th percentile strength
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 1a
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 1b
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 1c
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
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