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Complete workflow

Detailed sequence of a real RSL analysis, from input to report.

Overall scheme

INPUT                          CALCULATION                OUTPUT
─────                          ───────────                ──────
1. Stratigraphy                5. Discretisation          7. Surface PSA spectrum
2. Dynamic curves                  (sub-layers)            8. Input/output Fourier
   G/Gmax-γ + ξ-γ              6. Equivalent linear        9. γ/a/σ vs z profiles
3. Bedrock                          iterative →           10. FA/FH/FT factors
   accelerogram                     ↓                      11. Word report
4. Analysis type
   (single/multi-site)

1. Stratigraphy

Main page → Stratigraphy tab. For each layer define:

Field Unit Meaning
Thickness m layer thickness
Vs m/s shear-wave velocity (at small strain)
ρ (density) kN/m³ or kg/m³ density (unit weight / g)
G_max MPa computed as ρ · Vs² (default) or entered
ξ_min % minimum damping (small strain, typically 0.5-3%)
G/Gmax-γ curve — chosen from the library or custom
ξ-γ curve — chosen from the library or custom

The bottom layer is the bedrock, must have Vs ≥ 800 m/s and a depth such that seismic waves are effectively in 1D propagation.

2. Dynamic curves

RSL III ships with a library of standard literature curves:

  • Vucetic-Dobry (1991) — clays, function of PI
  • Seed-Idriss (1970) — sands, mid range
  • Darendeli (2001) — sands and clays, OCR- and σ'-dependent
  • EPRI (1993) — general
  • Custom curves — uploaded by the user as a γ → G/G_max and γ → ξ table

Each layer can be assigned a different pair of curves.

3. Input accelerogram

Input tab → load/paste the accelerogram at the bedrock (below the column). Supported formats:

  • PEER (text, standard header)
  • ITACA (Italian INGV format, text)
  • Generic (CSV with header time, accel)

The app auto-detects the Δt interval and total duration. Typical range: 20-40 seconds at Δt = 0.005-0.01 s.

Bedrock vs outcrop

Check whether your accelerogram is recorded on outcropping bedrock (outcrop) or inside the column (within). If it is outcrop and you enter it as within, you overestimate. RSL III treats the input as outcrop by default and applies the 1/2 correction in spectral deconvolution — see the FAQ if in doubt.

4. Analysis type

  • Single-site: 1 column × 1 accelerogram → deterministic spectrum
  • Multi-input: 1 column × N accelerograms (e.g. 7 recordings) → mean spectrum + envelope (recommended by NTC 2018 for advanced analyses)
  • Multi-column: comparison of different stratigraphies — useful for area-wide microzonation studies

5. Run the calculation

Press Run. RSL III:

  1. Discretises the column into sub-layers: max ~25 sub-layers to avoid aliasing at high frequencies (rule: Δh ≤ Vs / (4·f_max), with f_max typically 25 Hz)
  2. Computes the complex transfer function H(ω) between bedrock and surface (reflection/transmission coefficients method for plane shear waves in layered columns, frequency domain)
  3. Computes the output Fourier spectrum: F_out(ω) = H(ω) · F_in(ω)
  4. Inverse-transforms to get the surface accelerogram in time
  5. Estimates γ_max in each layer (γ_eff = 0.65 · γ_max per Idriss)
  6. Updates G_secant and ξ by reading the degradation curves at γ_eff
  7. Iterates until Δγ_eff < tolerance (default 0.5%, max 30 iterations)

See metodo.md for the mathematical details.

6. Inspect the results

Results tab → 4 panes:

Response spectrum

PSA (Pseudo Spectral Acceleration) or SA versus period T, 5% damping. Comparison with the reference NTC 2018 spectrum for the site (based on ground category, a_g, T_R). Where RSL > NTC = local amplification not captured by the standard NTC spectrum.

Fourier spectra

Input vs output, log-log scale. Shows the site amplification frequencies (f₀ = Vs / 4H for the first mode, higher modes at multiple frequencies).

Profiles along z

  • γ_max(z) in % — layers with γ > 0.1% are in non-linear regime
  • a_max(z) — acceleration amplification from bedrock to surface
  • σ_max(z) — maximum shear (kPa)

ICMS amplification factors

Summary table with FA, FH, FT (details in icms.md).

7. Export

Report toolbar. Generates a .docx structured for:

  • Level 3 seismic microzonation
  • Geological reports for structural design
  • Site seismic hazard studies

Summary diagram

flowchart TD
    A[Stratigraphy] --> D{Analysis type}
    B[Dynamic curves] --> D
    C[Input accelerograms] --> D
    D -->|Single| E[1 column × 1 input]
    D -->|Multi-input| F[1 column × N inputs]
    D -->|Multi-site| G[N columns × M inputs]
    E & F & G --> H[Iterative equivalent-linear]
    H --> I[PSA spectrum + γ/a/σ profiles]
    I --> J[ICMS factors FA/FH/FT]
    J --> K[Word report]

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