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How to do Systematic Risk Assessment of High-risk Structures Against Disproportionate collapse
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Systematic Risk Assessment of High-risk Structures against
Disproportionate Collapse
Based on IStructE guidelines
Harikrishnan Panikkaveettil
2. BACK GROUND AND DESIGN OBJECTIVES
Key Concepts and Eurocode Requirements
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Risk-based approach for design (against disproportionate collapse)
• Not a substitute for the lack of structural form
• Objectives
– Identify Hazards
– Eliminate the hazards
– Develop risk-reduction measures
• Level of detail – Engineer to decide
– Qualitative, Semi-quantitative & fully quantitative
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Risk
• Hazard: something which has the potential to cause harm
– Action on the structure
– “Soft” hazard [eg: failure to communicate effectively]
• Risk = Likelihood × Consequence
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Risk-based design
• “Acceptable level of risk” – unique for a structure
• Good risk management
– Costs of risk reduction ≈ magnitude of risk
• Secondary benefit
– Indentifying and communicating risks
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Reduction of risk
• Approach 1:
– Reduce all risk to threshold
• Approach 2:
– Reduce all risks so far as reasonably practicable(SFARP)
• Risks above threshold – unacceptable
As low as reasonably practicable
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Building risk classification
• Class 1
• Class 2A – Lower Risk Group
• Class 2B – Upper Risk Group
• Class 3 – High Risk Group
– “a systematic risk assessment of the building should be undertaken taking into account both foreseeable and unforeseeable hazards”
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3. DEVELOPMENT OF A SYSTEMATIC RISK ASSESSMENT
Framework for a systematic risk assessment
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Framework
• Single author – full responsibility
– Suitable Qualification and Experience (SQEP)
– Risk assessment workshop
– HAZard and Operability study (HAZOP)
• Framework
– Scenario-independent design
– Scenario-dependent design
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Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
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Likelihood scale
Likelihood Frequency Approximate return period
(based on 50 year design life)
Frequent/
common 10 times in design life Less than 1 in 10 years
Likely 50% probability of occurrence during design life 1 in 10 years to 1 in 100 years
Unlikely 10% probability of occurrence during design life 1 in 100 years to 1 in 1000 years
Rare 2% probability of occurrence during design life 1 in 1000 years to 1 in 10000 years
Improbably 0.1% probability of occurrence during design life 1 in 10000 years to 1 in 100000 years
Negligible Less than 0.1% probability of occurrence during design life Greater than 1 in 100000 years
Example Likelihood scale
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Parties involved in risk assessment
• Client/building owner
• Structural engineer (designer)
• Other designers
• External stakeholders
• Building control authority
• CDM coordinator/ risk management specialist
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Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 15 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 17 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
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(2) Eliminate the hazards
• Easier at the early stages of design
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Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 20 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 21 Harikrishnan Panikkaveettil
(3) Determine the tolerable risk threshold
• Extent of collapse for any given likelihood
• The threshold should be skewed towards consequence
– This effect diminishes beyond a certain point
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Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 23 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 24 Harikrishnan Panikkaveettil
(4) Evaluate the risk
• Risk = likelihood × consequence
• Watch points
– Sensitivity of solution/risk
7/18/2014 25 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 26 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
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(5) Identify risk reduction measures • Irrespective of level of risk
• Reduction of a risk may increase another risk
• Not limited technical
– “Soft” (procedural)
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Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 29 Harikrishnan Panikkaveettil
Identify the hazards
Eliminate the hazards if possible
Determine the tolerable risk level
Risk = Likelihood × Consequence
Identify risk reduction measures
Benefit / Cost assessment
Implement risk reduction
Residual risk
Sensitivity of the risk assessment
Review the overall level of risk Communicate
remaining risks
Rev
iew
1
2 3
4
5
6
7
8
9
7/18/2014 30 Harikrishnan Panikkaveettil