Eurocode 5 design in comparison with fire resistance tests of unprotected timber beams

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2 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

3 Introduction Timber in fire: Chars Contains moisture Has low thermal conductivity

4 Introduction Fire resistance: The time to failure (in minutes) of a structure or structural member exposed to a standard fire

5 Introduction Eurocode 5 calculations of fire resistance: Reduced cross-section method Reduced material property method Advanced method

6 Introduction Eurocode 5 calculations of fire resistance: Reduced cross-section method Reduced material property method Advanced method

7 Introduction Eurocode 5 calculations of fire resistance: Reduced cross-section method Reduced material property method Advanced method

8 Introduction Reduced cross-section method Reduced material property method Advanced method Require the original material properties (at ambient temperature)

9 Introduction Eurocode 5: Reduced cross-section method Most used Reduced material property method Advanced method

10 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

11 Reduced Cross Section Method of EC5 Adaptation of the 5th percentile strength

12 Reduced Cross Section Method of EC5 Adaptation of the 5th percentile strength

13 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

14 Method Comparative analysis: experimental results VS. predictions Predictions require the original material properties (at ambient temperature) 1. Strength grading Comparison 1 2. Reference tests 3. Young s modulus Comparison 2 (higher uncertainties) 4. Density

15 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

16 Comparison 1a

17 Comparison 1b 12 tests with given strength class VS. Predictions using: - The 5 th instead of the 20 th perc. strength - The zero strength layer according to EC5 As the characteristic strength is used, 95% of the predictions should be conservative

18 Comparison 1b

19 Comparison 1c 12 tests with given strength class VS. Predictions using: - The 5 th instead of the 20 th perc. strength - Double zero strength layer in comp. with EC5 As the characteristic strength is used, 95% of the predictions should be conservative

20 Comparison 1c

21 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

22 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 How??? As the estimated strength is used, 50% of the predictions should be conservative

23 Comparison 2a Estimation of the strength: Reference tests From the strength class From the Young s modulus From the Density

24 Comparison 2a Estimation of the strength: Reference tests From the strength class From the Young s modulus From the Density

25 Comparison 2a Estimation of the strength: Reference tests From the strength class From the Young s modulus From the Density

26 Comparison 2a Estimation of the strength: Reference tests From the strength class From the Young s modulus From the Density

27 tf;test Frequency (-) Comparison 2a Conservative tf;calculation 10% error 20% error Bending failure Nonconservative Shear/buckl. failure % normal distribution tf;test - tf;calculation (min)

28 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

29 tf;test Frequency (-) Comparison 2b This figure was corrected after the conference Conservative tf;calculation Unconservative This figure was corrected after the conference 50% error: tf;test - tf;calculation (min) Bending failure normal distribution expected normal distribution

30 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

31 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