Systematic Risk Assessment of High-risk Structures Against Disproportionate Collapse

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

7/18/2014 2 Harikrishnan Panikkaveettil

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


Risk

• Hazard: something which has the potential to cause harm

– Action on the structure

– “Soft” hazard [eg: failure to communicate effectively]

• Risk = Likelihood × Consequence


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


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


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”


3. DEVELOPMENT OF A SYSTEMATIC RISK ASSESSMENT

Framework for a systematic risk assessment


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


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


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


Consequence Scale


Risk Threshold


Parties involved in risk assessment

• Client/building owner

• Structural engineer (designer)

• Other designers

• External stakeholders

• Building control authority

• CDM coordinator/ risk management specialist
