Learning objectives
In this lesson
- Assess regularity before method selection.
- Look for demand concentration, not appearance alone.
Engineering explanation
Eccentric mass, stiffness or resistance can couple translation and rotation. Re-entrant geometry, diaphragm openings and offset resisting lines require explicit load-path and torsional review. Abrupt vertical changes can concentrate drift and force, including soft-storey, setback and transfer-level mechanisms. Classification must use the exact applicable edition criteria rather than visual judgement. The exercise below asks learners to diagnose an open ground storey, offset core, upper-storey setback and heavy rooftop plant.
Concept exercise
Identify the seismic irregularity
Identify the concern and the model or design question that follows.
Open ground storey
Investigate storey drift, mechanism formation and column demand.
Offset wall core
Examine stiffness centre, diaphragm transfer and edge displacement.
Upper-storey setback
Examine force transfer and demand near the transition.
Heavy rooftop plant
Verify mass modelling, local support and modal response.
Key takeaways
What to carry forward
- Assess regularity before method selection.
- Look for demand concentration, not appearance alone.
- Use verified edition criteria.