Aldring av konstruksjoner og betydning av robusthet

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1 Aldring av konstruksjoner og betydning av robusthet Egentlig robusthet og hva betyr det ifm aldring Gerhard Ersdal Principal Engineer, Petroleum Safety Authority Norway

2 Robusthet i Ptil regelverket Innretninger skal baseres på robuste og enklest mulige løsninger og utformes slik at: - de kan motstå laster, - storulykkesrisikoen blir så lav som mulig, - svikt i en komponent, i et system eller en enkelt feilhandling ikke gir uakseptable konsekvenser, - hovedsikkerhetsfunksjonene opprettholdes,

3 Robusthet i NORSOK N-001 (1) Load bearing structures shall have sufficient robustness to prevent that local damage or failure gives unacceptable consequences. Maritime systems shall have sufficient robustness to prevent that local damage or single technical or operational failures gives unacceptable consequences. Checking robustness covers an evaluation of the vulnerability of a structure or a maritime system in addition to the ALS check for accidental loads as described in a risk analysis. It should include an evaluation of the vulnerability of the structure or the maritime system for - local errors in design, fabrication and operation, - damages or human errors in installation and operation.

4 Robusthet i NORSOK N-001 (2) It is normally assumed that such errors and damages are restricted to a local area, or to a single event. This check is not intended to cover fundamental or systematic failures in the design, fabrication or operation. Basis for check of local damage and failure of structures shall be based on the ALS principle as stated in 6.2. All maritime systems shall be categorized with regards to safety criticality, redundancy and robustness. Proper maintenance- and spare part philosophy shall be demonstrated for all essential maritime systems.

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6 litteratur-studie A robust system tolerates adverse or unexpected conditions (Taleb, Black Swan ) Robustness is the property of systems that enables them to survive unforeseen or unusual circumstances (Knoll and Vogel 2009). Robustness refers to the insensitivity of performance to deviations from the normal conditions (Aven Risk analysis, 2008). the ability of a system to resist change without adapting its initial stable configuration (Wikipedia 2014) designing a system to be resistant to total failure despite partial damage (Wiktionary 2014) ISO 19900:2013 the ability of a structure to withstand accidental and abnormal events without being damaged to an extent disproportionate to the cause.

7 Robustness refers to the insensitivity of performance to deviations from the normal conditions (Aven Risk analysis, 2008). Causes Initiating event Consequences Vulnerability / Robustness Sensitivity to deviations from normal conditions Vulnerability / Robustness Sensitivity to the occurrence of the initiating event

8 Tradisjonell tanke om robusthet Causes Initiating event Consequences Vulnerability / Robustness Sensitivity to deviations from normal conditions Vulnerability / Robustness Sensitivity to the occurrence of the initiating event ALS Damage tolerance 1986 version of ISO 2394 [Structures] should, in general, retain sufficient integrity to withstand local failure and specified accidental events such as explosions, fire and vehicular impact.

9 Prinsipper for sikre konstruksjoner (ISO 2394:2013, EN 1990 etc ) Knowing and controlling the hazardous events and actions Limiting the structure s sensitivity to the hazardous events and actions Ensuring the structural elements are able to withstand the stresses from the experienced hazardous events and actions (limit state design) beyond the theoretical minimum Ensuring that single structural element failure is visible or detectable prior to a complete collapse of the structure. Ensuring that the structure has the necessary damage tolerance. Reduction of the consequences of a collapse of the structure.

10 Goal Principles Methods Typically found in laws and regulations. E.g. PSA requirement of prudent design, withstanding 10-4 hazards and actions. Typically found in high level standards. E.g. ISO 2394 requirement of withstanding actions, robustness, competency and quality assurance. Methods will include how the principles should be implemented. E.g. by the use of LRFD or WSD to withstand actions. E.g. ISO 2394 or ISO Details on how to apply methods Criteria for acceptance Detailed design requirement for specific structures Details on applying the methods may include characteristic values for actions and resistance for LRFD design. E.g. NORSOK standards. Typically includes action and resistance factors and combinations of actions. E.g. NORSOK standards. Rules for specific structural types based on the above principles, methods and acceptance criteria. E.g. ship rules.

11 Goal Principles Robust løsning Risikoanalyse er ikke konstruksjonsingeniørenes sterke side, så dette må detaljeres ut I metoder 6 prinsipper + krever risikoanalyse for kategori 4 og 5 konstruksjoner Methods Details on how to apply methods Criteria for acceptance ISO og N-001 tar vel kanskje ikke dette godt videre til praktiske metoder. Bortsett fra ALS og Skadetoleranse Få detaljer om hvordan robusthet skal faktisk sjekkes. Bortsett fra ALS og skadetoleranse Få eller ingen kriterier Bortsett fra ALS og skadetoleranse Detailed design requirement for specific structures

12 Hazardous event control Limiting sensitivity to hazard Load resistance Visible / detectable damage Damage tolerance Reduction of consequences Har dette noen link til barrierer? Causes Initiating event Consequences Vulnerability / Robustness Sensitivity to deviations from normal conditions Vulnerability / Robustness Sensitivity to the occurrence of the initiating event

13 Performance requirements GEr Functional Integrity Robustness Barrier's effect on the chain of events assumed that the barrier function as intended Barrier's ability to be present and intact at all times Barrier's ability to survive in hazardous and accidental situations

14 Hvordan påvirkes disse prinsippene eller hva-de-nå-skal-hete av aldring? Hazardous event control Limiting sensitivity to hazard Load resistance Visible / detectable damage Damage tolerance Reduction of consequences Causes Initiating event Consequences Vulnerability / Robustness Sensitivity to deviations from normal conditions Vulnerability / Robustness Sensitivity to the occurrence of the initiating event

15 Robust konstruksjon vs robust design og analyse Hva er det som skal være robust? Konstruksjonen eller analysene og designprosedyrene? Eller begge? Må vi ha robuste analyser (sjekke sensitivitet til elementmodeller, randbetingelser, demping, ++++) for å få robuste konstruksjoner?

16 Oppsummering N-001 om robusthet bør oppdateres Noen ideer for hva som bør legges inn i robusthet er presentert Er dette gode ideer? Hvordan kan vi få det til å bli praktisk (nok)? Hva betyr aldring for dette? Beholder konstruksjonene sin robusthet?