Extreme-event foundations · Risk and performance
From Scenario to Performance Decision
Turn an extreme-event scenario into a traceable chain of loading, response, damage, consequence, and engineering action.
Learning objectives
By the end of this lesson
- Separate likelihood and consequence from structural resistance calculations.
- Build a hazard–load–response–damage–consequence chain.
- Define performance objectives before selecting analysis fidelity.
- Use screening scores without confusing them with design acceptance criteria.
Before you calculate
What this means in the real world
What the formula is for
A simple matrix can help rank scenarios using agreed ordinal likelihood and consequence ratings. The multiplication is a prioritization device, not a physical law and not a structural safety equation.
S = L × CWhere an engineer uses it
Impact near an occupied entrance: The same barrier calculation can lead to different decisions when occupancy, stand-off, access control, and post-event function change.
Define the vehicle scenario, impact geometry, transferred action, barrier response, breach or debris criteria, and the consequence of loss of function.
What a wrong value can do
A wrong unit, sign, scale, boundary condition, or property can produce a believable number with the wrong physical meaning. It may understate demand, exaggerate it, or lead to the wrong failure check.
Definition
Performance objective
A clear statement of the condition or function a structure should maintain, or the damage it may tolerate, for a defined event scenario.
Start with a scenario, not a formula
An extreme-event assessment begins by describing what may happen, where it may occur, what is exposed, and which consequences matter. The structural calculation occupies the middle of this chain. It translates an applied action into response and damage, but it does not independently define likelihood or acceptable consequence.
Formula
Illustrative risk-screening index
A simple matrix can help rank scenarios using agreed ordinal likelihood and consequence ratings. The multiplication is a prioritization device, not a physical law and not a structural safety equation.
- L
- illustrative likelihood category, defined by the project authority
- C
- illustrative consequence category, defined by the project authority
- S
- screening score used only for prioritization
Scenario chain experiment
Trace the scenario chain
Switch between impact and blast scenarios, then change illustrative likelihood and consequence ratings to see how analysis priority can change without altering structural capacity.
This score demonstrates prioritization logic only. Project risk categories and acceptance criteria must come from the responsible authority.
The five links that must stay visible
Hazard describes the initiating event. Load describes what reaches the structure. Response describes motion, force, stress, or deformation. Damage describes the physical condition created by that response. Consequence describes effects on people, function, assets, and surrounding systems. Each transition has assumptions that should be recorded and tested.
Real-world application
Impact near an occupied entrance
The same barrier calculation can lead to different decisions when occupancy, stand-off, access control, and post-event function change.
- Modelling move
- Define the vehicle scenario, impact geometry, transferred action, barrier response, breach or debris criteria, and the consequence of loss of function.
- Engineering question
- Which uncertainty most strongly changes the required performance objective?
Real-world application
External blast near an essential facility
Structural survival alone may not preserve essential function if façades, utilities, equipment, or access routes fail.
- Modelling move
- Connect component response limits to system-level continuity and credible progressive consequences.
- Engineering question
- What must remain operational after the event, and what controlled damage is acceptable?
Editable formula question
Calculate an illustrative screening score
Choose project-defined example ratings and calculate their product. Use the result only to practise prioritization logic.
The displayed minimum, maximum, and textbook values define this learning exercise only. They are not universal design limits.