Cumulative tutorial 15
Yield, or isolate
Two ways to survive the same earthquake, and what each does to the building.
The same client, the same site, two schemes. Scheme A is a ductile frame that yields — the previous tutorial's frame. Scheme B puts the building on isolators and keeps it elastic. Quantify both, then compare what they demand of the rest of the building.
What you are given
- Scheme A: the ductile frame, k = 9.5 MN/m, fy = 420 kN, α = 0.03, T = 0.75 s, μ = 3.2
- Scheme B: total mass above the bearings 3 600 tonnes, fixed-base period 0.55 s, target isolated period 3.2 s
Tutorial 15
Work the problem
4 questions
Question 1
Scheme A: what is the secant stiffness at peak response, in MN/m?
Question 2
Scheme A: what effective period does that give, in seconds?
Question 3
Scheme B: what total isolator stiffness gives a 3.2 s period, in MN/m?
Question 4
Scheme B: what period shift does that achieve, against the 0.55 s fixed-base period?
What this establishes
Scheme A reaches an effective period of 1.30 s by damaging itself, and the damage is the mechanism. Scheme B reaches 3.2 s by design, stays elastic, and puts all the movement in bearings that can be inspected and replaced. Scheme A is cheaper to build; Scheme B is far cheaper to own after an event, which is why hospitals and data centres choose it.