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PROBLEMS IN THE CURRENT EUROCODE Tikkurila 5.5.2011 T. Poutanen

PROBLEMS IN THE CURRENT EUROCODE Tikkurila 5.5.2011 T. Poutanen.

larissa-peterson
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PROBLEMS IN THE CURRENT EUROCODE Tikkurila 5.5.2011 T. Poutanen

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  1. PROBLEMS IN THE CURRENT EUROCODETikkurila 5.5.2011T. Poutanen

  2. In the current EUROCODE loads arecombined in three contradicting ways (error …-20 %) : a:Dependently, permanent loads, loads are at the target reliability values,b:Independently, gG, gQ,gM, loads have random values (Borges-Cashaheta), c:Semi-dependently, y0, one load has random the other the target value (Turkstra)loads must always be combined dependently Variation of variable load is assumed constant VQ = 0.4 (error -10…+40 %) : Material safety factors gM are assumed constant (error …+20 %): Load factors are non-equal gG ≠ gQ , gQ = gQ = 1 results in the same outcome with less effort Summary

  3. Permanent load G: normal distribution, design point value: 0.5, VG = 0.0915 (corresponding to gG=1.35) • Variale load Q:Gumbel distribution, design point value: 50 year value i.e. 0.98-value, VQ = 0.4 (in reality 0.2-0.5) • Materiat M:Log-normal distribution, design point value: 0.05-value, VMsteel0.1, Vmglue-lam0.2, VMtimber0.3 • Code, design, execution and use variabilities are usually included in the V-values Basic assumptions:

  4. Comparison of distributions, m = 1, s = 0.2 Permanent load Solid line Normal Cariable load Dashed line Gumbel Material Dotted line Log-normal

  5. Normal • Gumbel • Log-normal Distributions:

  6. Basic equations:

  7. EC distributions assigned to the design point 1 The design point is selected at unity i.e. 1 Permanent load VG=0.091, solid line Variable load VQ=0.4 dash-dotted line, VQ=0.2,0.5 dot line Material VM=0.1, 0.2, 0.3, dashed line

  8. EC distributions at failure state (Finland) Permanent load VG=0.091, gG = 1.35 , solid line Variable load VQ=0.4,gQ = 1.5, dash-dotted line Material VM=0.1, 0.2, 0.3, gM ≈ 1.0, 1.2, 1.4, dashed line

  9. VM= 0.3 (Sawn timber) VM = 0.2 (Glue lam) EC gM-values if gG = 1.35, gQ = 15, calculated - dependently, thick solid line fractile sum method, thin solid line normalized convolution equation- independently, dotted line, convolution equation, Borges-Castanheta-method- Semi-dependently, Tursktra’s method , dashed line VM = 0 (Ideal material) VM = 0.1 (Steel) • (load ratio, • variable load/total load) gM 

  10. VM = 0.3 (Sawn timber) EC gM-values, independent combination VM = 0.2 (Glue lam) VM = 0.1 (Steel) gG,Q Permanent load VG=0.091, gG = 1.35 Variable load VQ=0.2, 0.4, gG = 1.5 Material VM = 0.1 (≈steel), 0.2 (≈glue lam), 0.3 (≈sawn timber) Dotted lines denote VQ=0.2 calculation, solid lines to VQ=0.4 calculation Permanent load a (load ratio, variable load/total load) Variable load

  11. VM = 0.3 (Sawn timber) EC gM-values, dependent combination VM = 0.2 (Glue lam) VM = 0.1 (Steel) gG,Q Permanent load VG=0.091, gG = 1.35 Variable load VQ=0.2, 0.4, gG = 1.5 Material VM = 0.1 (≈steel), 0.2 (≈glue lam), 0.3 (≈sawn timber) Dotted lines denote VQ=0.2 calculation, solid lines to VQ=0.4 calculation Permanent load a (load ratio, variable load/total load) Variable load

  12. Ideal material, V = 0 Independent gGQ,-calculation when gM-values are known: Dashed lines denote Finnish gGQ–values: gG = 1.15, 1.35, gQ = 1.5 Steel, V = 0.1, gM = 1.0 Rule 6.10a,mod Glue lam, V = 0.2, gM = 1.2 Sawn timber, V = 0.3, gM = 1.4 a (load ratio, variable load/total load)

  13. Ideal material, V = 0 Dependent gGQ,-calculation when gM-values are known: Dashed lines denote Finnish gGQ–values: gG = 1.15, 1.35, gQ = 1.5 Steel, V = 0.1, gM = 1.0 Rule 6.10a,mod Glue lam, V = 0.2, gM = 1.2 Sawn timber, V = 0.3, gM = 1.4 a (load ratio, variable load/total load)

  14. Partial factor design code can be converted into a permissible stress /total safety factor code in three optional ways: Option 2 Option 3 Option 1

  15. EC Serviceability EC Failure A new(old) method Safety factors are not imperative gG,Q G: solid Q: dashed VQ = 0.4 M: dotted, gM- values are selected in a way the target reliability is obtained if the load combination has more than 10 % G or Q 0.99922904  1297 years

  16. VM= 0.3 (Sawn timber) EC gT-values if gG = 1, gQ = 1, calculated dependently VM = 0.2 (Glue lam) Permanent load VG=0.091, gG = 1 Variable load VQ = 0.2, dp = 0.96, gQ = 1 VQ = 0.4, dp = 0.98, gQ = 1 Material VM= 0.1 (≈steel), 0.2 (≈glue lam), 0.3 (≈sawn timber) gG,Q VM = 0.1 (Steel) gT  Permanent load Variable load a (load ratio, variable load/total load) VM = 0.1: gTC.0.1 = 1.4 + a*0.35 (1.4…1.74) VM = 0.2: gTC.0.2 = 1.64 VM = 0.3: gTC.0.3 = 1.99 - a* 0.33, 0 a < 0.6, 1.8, 0.6 a1 (1.99…1.66)

  17. How time is considered in designCurrent snow codeCurrent wind codeCorrect equationTime is considered in the variable load safety factor gQ only : gG,Q

  18. A MODIFIED EUROCODE: Load factors should be removed gG = gQ = 1, accuracy remainsMaterial factors gM should be set variable, accuracy inceases by ca 20 %The design point value of the variable load should be set variable ca 25…50 years, accuracy increases by ca 40 %Combination factors 0 should be updated The reliability error of the modified eurocode is 0…10 % with less calculation work (current eurocode -20…+60 %) Eurocode should have a compatibility condition

  19. Thank you for your attention

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