Which equations are implemented?

ASCE 7-22 ELF: V=Cs·W; Cs base = SDS/(R/Ie); caps Eq. 12.8-3 (T ≤ TL) and 12.8-4 (T > TL); minimums Eq. 12.8-5/12.8-6 including 0.044·SDS·Ie ≥ 0.01 and near-fault 0.5·S1/(R/Ie) when S1 ≥ 0.6.

Where do Fa and Fv come from?

From ASCE tables by Site Class and Ss/S1 with straight-line interpolation between tabulated points. Always confirm with the ASCE Hazard Tool or geotechnical report.

Does the tool handle Site Class F?

Yes — it disables Auto-fill and prompts for site-specific procedures. Enter Fa and Fv from a site-specific analysis if applicable.

ASCE 7-22 Seismic Design Calculator

Q: Is the result suitable for final design?

Use results as a professional aid. Final design must follow ASCE 7-22 and local amendments and be verified by a licensed engineer.

This professional-grade calculator implements the ASCE 7-22 Equivalent Lateral Force (ELF) procedure to compute base shear $ V = C_s \cdot W $. It auto-fills $F_a$ and $F_v$ from Site Class (A–F) via straight-line interpolation, applies caps (Eqs. 12.8-3/12.8-4) and minimums (Eqs. 12.8-5/12.8-6), and outputs a clear audit trail.

Calculator

Units

Risk Category → Importance $I_e$

Site Class

Auto-fill $F_a, F_v$

Mapped short-period $S_s$ (g)

Mapped 1-sec $S_1$ (g)

Site coefficient $F_a$

Site coefficient $F_v$

Long-period transition $T_L$ (s)

Fundamental period $T$ (s)

Response modification $R$

Effective seismic weight $W$

Results

$S_{MS} = F_a \cdot S_s$ —

$S_{M1} = F_v \cdot S_1$ —

$S_{DS} = \tfrac{2}{3} S_{MS}$ —

$S_{D1} = \tfrac{2}{3} S_{M1}$ —

Governing $C_s$ —

Base shear $V = C_s \cdot W$ —

Data Source and Methodology

ASCE/SEI 7-22 — Minimum Design Loads and Associated Criteria for Buildings and Other Structures. Official overview: ASCE 7-22. This tool implements ELF equations 12.8-1 through 12.8-6, including caps (12.8-3/12.8-4) and minimums (12.8-5/12.8-6).
Site Parameters: Use the ASCE Hazard Tool (project location) or your geotechnical report to obtain $S_s, S_1, F_a, F_v, T_L$.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Design spectra:

$$ S_{MS} = F_a S_s,\quad S_{M1} = F_v S_1,\quad S_{DS} = \tfrac{2}{3}\,S_{MS},\quad S_{D1} = \tfrac{2}{3}\,S_{M1} $$

Response coefficient and base shear:

$$ C_s = \min\!\left( \frac{S_{DS}}{R/I_e},\; \begin{cases} \dfrac{S_{D1}}{T\,(R/I_e)}, & T \le T_L \\\\ \dfrac{S_{D1}\,T_L}{T^2\,(R/I_e)}, & T > T_L \end{cases} \right), \qquad V = C_s\,W $$

Minimums:

$$ C_s \ge \max\!\left(0.01,\; 0.044\,S_{DS}\,I_e,\; \mathbb{1}_{S_1\ge 0.6}\cdot \frac{0.5\,S_1}{(R/I_e)}\right) $$

Glossary of Variables

$S_s, S_1$ — Mapped spectral accelerations (short-period, 1-sec).
$F_a, F_v$ — Site coefficients (from Site Class and $S_s, S_1$).
$S_{MS}, S_{M1}, S_{DS}, S_{D1}$ — Adjusted MCE and design spectral parameters.
$T$ — Fundamental period (modal or approximate $T_a$).
$T_L$ — Long-period transition.
$R$ — Response modification factor (by system).
$I_e$ — Seismic importance factor (by Risk Category).
$W$ — Effective seismic weight; $C_s$ — response coefficient; $V$ — base shear.

How It Works: A Step-by-Step Example

Case: Site Class D, $S_s=1.0$, $S_1=0.4$, $T_L=8.0\,\mathrm{s}$, $T=0.8\,\mathrm{s}$, $R=8$, $I_e=1.0$, $W=25{,}000\,\mathrm{kN}$. Interpolated $F_a\approx1.10$, $F_v\approx1.60$.

$S_{MS}=F_a S_s=1.10$; $S_{M1}=F_v S_1=0.64$.
$S_{DS}=\tfrac{2}{3} S_{MS}=0.733$; $S_{D1}=\tfrac{2}{3} S_{M1}=0.427$.
Base $C_s=S_{DS}/(R/I_e)=0.0916$; cap $C_s=S_{D1}/(T(R/I_e))=0.0667$ ⇒ governing $C_s=0.0667$.
Minimums: $0.044S_{DS}I_e=0.0323$; $0.01$; near-fault N/A ($S_1<0.6$). Governed by cap.
Base shear: $V=0.0667 \times 25{,}000 = 1{,}667\,\mathrm{kN}$.

Frequently Asked Questions (FAQ)

Where do I get $S_s$, $S_1$, $F_a$, $F_v$, and $T_L$?

From the ASCE Hazard Tool for your site or from a geotechnical report.

Does the tool apply the near-fault minimum?

Yes — if $S_1 \ge 0.6$, it applies $C_s \ge 0.5\,S_1/(R/I_e)$ in addition to other minimums.

What if my site is Class F?

Auto-fill is disabled and a site-specific ground motion procedure is generally required. Enter $F_a, F_v$ only from a site-specific analysis.

Can I override $F_a$ and $F_v$?

Yes — switch Auto-fill to Off and input values from the Hazard Tool/report.

Does this compute Seismic Design Category (SDC)?

No; this tool focuses on $V$. Use $S_{DS}$, $S_{D1}$, and Risk Category with §11.6 to determine SDC.

Is this enough for final design?

Use results as a professional aid. Final design must follow ASCE 7-22 and local amendments, and be checked by a licensed engineer.

Tool developed by Ugo Candido. Content verified by CalcDomain Engineering Editorial Team.
Last reviewed for accuracy on: September 22, 2025.