Ground engineering · Earthquake geotechnics
Seismic hazard & base shear (AS 1170.4) calculator
Hazard factor and return period to design spectrum for site classes Ae–Ee, natural period and base shear distributed up a regular building.
Standard: AS 1170.4-2007 (Amdt 2) · equivalent static Cl 6
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Hazard factor Z (read from AS 1170.4 Table 3.2 / Fig 3.2) | 0.08 | |
| Annual probability of exceedance 1/R | 1/500 | |
| Site sub-soil class | Ce shallow soil | |
| Building height hn | 12 | m |
| Number of storeys | 4 | |
| Period factor kt | 0.075 concrete moment frame | |
| Seismic weight per floor (G + ψcQ) | 3000 | kN |
| Ductility μ | 2 | |
| Structural performance factor Sp | 0.77 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Return-period factor kp | 1.00 | |
| kp·Z (min 0.08) | 0.080 | |
| Natural period T1 = 1.25·kt·hn^0.75 | 0.604 | s |
| Spectral shape Ch(T1), class Ce | 2.068 | |
| Cd(T1) = kpZ·Ch·Sp/μ | 0.0637 | |
| Total seismic weight | 12,000 | kN |
| Base shear V | 764 | kN |
| Distribution exponent k | 1.05 | |
| Ground acceleration ≈ kpZ·Ch(0) | 0.104 | g |
- ✓ Regular building, equivalent static applicable (check EDC / height limits)
- ✓ Base shear ≥ 0.01W (practical lower bound)
Method, formulas and assumptions
- kp from AS 1170.4 Table 3.1; (kp·Z) not less than 0.08
- T1 = 1.25·kt·hn^0.75 (Cl 6.2.3)
- Ch(T) from Table 6.4 for the site class
- V = Cd(T1)·Wt with Cd = kpZ·Ch(T1)·Sp/μ
- Fi = kF,i·V, kF,i = Wi·hi^k / Σ(Wj·hj^k); k = 1 (T ≤ 0.5 s) to 2 (T ≥ 2.5 s)
- Read Z for your site from the current AS 1170.4 Table 3.2 or hazard map; the default is only an example.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.