Cumulative tutorial 20
One building, end to end
The whole course applied to a single structure, and the decision it leads to.
A client owns the three-storey building analysed in tutorials 8 to 13. An assessment has found the base shear coefficient uncomfortably high, and three options are on the table: accept ductile yielding, isolate, or add dampers. Use what has already been computed to compare them on one page.
This is the tutorial that asks whether you can move between the methods rather than within one.
What you are given
- Three storeys, 1 200 tonnes total, T₁ = 0.3157 s, first-mode effective mass 91.41%
- Elastic base shear from the spectrum analysis 5.615 MN; seismic weight 11.77 MN
- Ductile option: μ = 3.0 available with the proposed detailing
- Isolation option: target isolated period 2.8 s
- Damper option: six dampers, each adding 1.11% to the first mode
Tutorial 20
Work the problem
4 questions
Question 1
What is the current elastic base shear coefficient?
Question 2
Ductile option: using the equal-energy rule at this short period, what strength reduction does μ = 3.0 give?
Question 3
Isolation option: what period shift does moving from 0.3157 s to 2.8 s achieve?
Question 4
Damper option: six dampers add 6.66% to the inherent 2%. Taking resonant response as proportional to 1/ζ, by what factor does the response fall?
What this establishes
Three defensible answers, and they are not interchangeable. Ductility is cheapest to build and damages the building by design. Isolation gives the largest force reduction and demands a moat, flexible services and bearings that can be inspected. Dampers give a moderate reduction, leave the period alone and therefore leave the foundations alone. Which is right depends on what the client values after an event — and that is an engineering judgement the analysis informs rather than makes.