Eurocodes failing to standardise safety Mike Byfield, Cranfield

Eurocodes  failing to standardise safety Mike Byfield, Cranfield

Eurocodes failing to standardise safety Mike Byfield, Cranfield University The Eurocode approach to partial safety factors The structural Eurocodes aim to restrict the probability of the actual resistance of structural components falling below the design resistance to 1 in 845 (approximately 10 -3). CEN have adopted what is known as a boxed values approach to M-factors. Each member state selects its own M values, which are applied to a whole range of different resistance functions.

Advantage Political: It retains the authority of member states to set the safety levels achieved by the codes. Disadvantage structural reliability: The system cannot account for variations in the quality of the design expressions The probability of the resistance falling below the design resistance is influenced by 3 factors: Reliability of material and geometric properties Design expression accuracy The value of partial safety factor, M

Predicted strength Design expression accuracy Series1 Series2 K Experimental strength

Comparison between poor and high quality design expressions Examples of variations in design expression accuracy Three different resistance functions have been investigated: Tensile resistance of bolts (based on 135 direct tensile tests on 20mm diameter grade 8.8 ordinary bolts) Bending resistance of restrained beams (based on 20 tests with restraints selected to produce a worst-case scenario) The shear buckling resistance of plate girders (based on 35 plate girder tests)

Results from reliability analysis Design task Probability of actual strength falling below the design strength <10-8 R* Safety factor to achieve the

Bending resistance of restrained beams 4.6x10-6 0.95 (1.10) Shear buckling resistance of plate girders

1.0x10-2 1.33 (1.10) Tensile resistance of ordinary bolts target reliability, existing M factor in brackets 0.95 (1.25)

Conclusions from the reliability analysis The most complex design task requires the highest safety factor. Reliability variations can reduce safety by leading to over-strength components, transferring failure to connections or columns Increasing the boxed value to improve the reliability of plate girder design would not necessarily solve all the reliability problems. A practical solution to variable safety levels Solution 1 Determine a M factor for each resistance function. The factor could take

the form of a numerical constant incorporated into the design expression Designer being largely unaware of the origin of the factor. No other safety factors on resistance. Problem politically unacceptable Solution 2 Retain the boxed value system Embed a supplementary safety factor into each resistance function. The boxed values selected by nation states would merely adjust design economy and target reliability.

M Supplementary factor, k = * R Where: M is the boxed value *R is the safety factor output from reliability analysis

Thus the design resistance, rd = k rn / M Example In the case of the plastic moment capacity of restrained beams k = 1.10 / 0.94 = 1.17 The modified design expression would take the form: M pl.Rd 1.17 Wpl f y / M 0 This would offer a 17% increase in the design moment, whilst still

achieving the target reliability. During the calibration of k factors it may be desirable to adjust the target reliability depending on the consequences of failure. 1.0E-08 1.0E-07 1.0E-07 Reliability, Pr(r

Reliability, Pr(r

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E-01 1.0E+00

1.0E+00 Individual design expressions Current variations in reliability Individual design expressions Variations in reliability using the supplementary safety factors

Recently Viewed Presentations

  • ILE2D with Omron CJ1M PLC. - Schneider Electric

    ILE2D with Omron CJ1M PLC. - Schneider Electric

    Quantum red RIO Centro de Competencia Técnica 8.1 Cable Simple Coaxial Lineal 8.2 Simple Cable Coaxial Ramificada 8.3 Configuraciones coaxial no permitidas 7.1 Cable Redundante Coaxial Lineal 7.2 Cable Redundante Coaxial Ramificada 7.3 Configuraciones coaxial no permitidas 6.1 Cable Simple...
  • LPSS Budget Workshop 04/18/02

    LPSS Budget Workshop 04/18/02

    Budget Preparation Calendar Budget Workshop Agenda for May 29, 2002 Custodial Services - Staffing Custodial Services - Staffing Custodial Services - Staffing ADDITIONAL RECOMMENDATIONS A minimum of 2.0 Custodial Positions are recommended at each school site.
  • Explicating Poems

    Explicating Poems

    Using TP-FASTT. Title: Introduction to Poetry - introducing how to approach a poem AND introducing this poem. Paraphrase: Explaining how a poem should be treated versus how some/many treat one
  • Prezentacja programu PowerPoint

    Prezentacja programu PowerPoint

    Jednak wiele z nich nie zostało jeszcze odkrytych, liczba ta może wynosić nawet 80%. Potwierdza to raport organizacji ekologicznej WWF, który podaje, że na każde trzy dni ostatniej dekady przypada odkrycie jednego nowego gatunku. Przez Amazonię przepływa najdłuższa rzeka świata...
  • Operations and Competitiveness - Hatem Masri

    Operations and Competitiveness - Hatem Masri

    Determining order winners and order qualifiers. What qualifies an item to be considered for purchase? What wins the order? Positioning the firm. How will the firm compete? Deploying the strategy. Strategic Planning. Mission. and Vision. Corporate. Strategy. Operations. Strategy. Marketing.
  • BNI 10 Minutes April 2013 - positivenetworking.co.uk

    BNI 10 Minutes April 2013 - positivenetworking.co.uk

    Sphere Risk Health & safety management Ltd. Set up 2005 after two years as a sole trader. Diplomas Pts 1 & 2. Chartered 2005 / OSHCR 2015. Look after some 250 clients with 8 staff
  • Chapter 2 (Handout 1 only sections 2.1, 2.2

    Chapter 2 (Handout 1 only sections 2.1, 2.2

    Chapter 2 (Handout 1- only sections 2.1, 2.2 and 2.3) Dr. Clincy Professor of CS Dr. Clincy Lecture * * * * Dr. Clincy Intro and Lecture * OSI Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains...
  • The Transition from the Classical period to the Hellenistic ...

    The Transition from the Classical period to the Hellenistic ...

    This transition between the classical and Hellenistic period caused the narratives told through the artwork to express scenes that depicted action and that dealt with pain and suffering. The classical period of course had events that dealt with this, but...