Stability or Operability — Which Seismic Verification Do You Need?
People often speak of "the seismic verification" as if it were one thing. In fact there are two fundamentally different verifications — and confusing them is expensive. One allows the component to deform permanently. The other requires it to still work afterwards. Carry out the wrong one, and you either do too much work or verify the wrong thing.
Stability Verification: It May Break, but It Must Not Fall Over
The stability verification has a clear, narrowly defined purpose: to ensure that, in the event of an earthquake, the component and its fixing bolts do not fracture, slip or topple — so that no lives are endangered.
What is explicitly permitted here: significant plastic deformation. The component may bend permanently, dent, become unusable. Whether it still performs its function after the earthquake is irrelevant to this verification — it only has to stay in place and injure no one.
That makes the stability verification comparatively forgiving: because plastic reserves may be used, higher stresses are admissible.
Operability Verification: It Has to Keep Running
The operability verification is considerably more demanding. Here it must be demonstrated that the component retains its full function during and after the earthquake.
A clear example: for a pump, it must be ensured that the rotating impeller does not rub against the casing during a seismic event, and that the seismic acceleration does not produce impermissibly high stresses that impair function. The permanent deformations that were still acceptable for the stability verification are usually off-limits here — a permanently deformed component rarely works as intended.
Which One Do You Need?
The answer does not depend on the calculation, but on the question of what the component must do during and after the earthquake:
- Is it enough that a structure stays standing and endangers no one? → stability verification
- Must a safety-relevant component keep working reliably after the quake — a coolant pump, a valve, an emergency power supply? → operability verification
This classification is best made before any calculation begins. It determines the admissible limits, the choice of analysis method, and therefore the effort and cost.
Conclusion
"The seismic verification" is not a single, well-defined task. Only deciding whether stability or operability is required makes the task calculable — and prevents you from verifying the wrong thing.
Unsure which verification applies to your component? We will clarify it with you and carry out the seismic analysis to EN 1998, ASCE 7, IBC, UBC or KTA. Contact us.
