Home / Tools / ASCE 7-22 Seismic ELF 🇺🇸 US · B

ASCE 7-22 — Equivalent Lateral Force

Seismic response coefficient Cs · Approximate period Ta · Base shear V = Cs·W · Vertical distribution of seismic forces Fx · Story shear Vx

Seismic Parameters

Ss (mapped MCE, g)

From USGS seismic design maps

S1 (mapped MCE, g)

Fa (site coeff. short)

Table 11.4-1

Fv (site coeff. 1-sec)

Table 11.4-2

R — Response modification factor

Ie — Importance factor

Structure type (for Ta)

Building Data

Total seismic weight W kip

Building height hn ft

Number of stories

T analytical (optional, from modal analysis) s

If given, T = min(T_analytical, Cu·Ta) per §12.8.2 / Table 12.8-1

Story weights are assumed equal (W/n per floor)

Seismic Design Results

SDS §11.4.4—

SD1—

SDC Tables 11.6-1/2—

Ta (approx. period) Eq.12.8-7 s—

Cu · Ta (period cap) Table 12.8-1 s—

T used—

Governing Cs equation—

Cs (Eq.12.8-2)—

Cs,max (Eq.12.8-3)—

Cs,min (Eq.12.8-5)—

V = Cs·W Eq.12.8-1 kip—

k (distribution exponent)—

Code References

§11.4.4SDS = (2/3)·Fa·Ss ; SD1 = (2/3)·Fv·S1

Eq.12.8-7Ta = Ct·hn^x (approximate fundamental period)

Eq.12.8-2Cs = SDS/(R/Ie)

Eq.12.8-3Cs ≤ SD1/(T·R/Ie) for T ≤ TL

Eq.12.8-5Cs ≥ max(0.044·SDS·Ie, 0.01)

Eq.12.8-1V = Cs·W (seismic base shear)

Eq.12.8-4Cs ≤ SD1·TL/(T²·R/Ie) for T > TL

Eq.12.8-6Cs ≥ 0.5·S1/(R/Ie) where S1 ≥ 0.6g — floor applied AFTER the cap (ordering verified by regression test)

Table 12.8-1Cu upper-limit coefficient on calculated period: T ≤ Cu·Ta (1.7…1.4, interpolated on SD1)

Tables 11.6-1/2Seismic Design Category from SDS and SD1 (higher governs); S1 ≥ 0.75g → E/F

Verificationengine/asce7-seismic.js — 50/50 tests: two external anchors (civilmat; SkyCiv doc example corrected via internal-consistency audit), all five Cs branches, Cu interpolation, 8 SDC cases. A third candidate source was REJECTED for an arithmetic error (78^0.8 misstated). One real ordering bug found in us-codes.js and fixed with a regression test.

Eq.12.8-11,12Fx = Cvx·V ; Cvx = wx·hx^k / Σ(wi·hi^k)

Engine: us-codes.js + asce7-seismic.js · US-ASCE7-22.v2 · 50/50 external-anchor tests ·

← ACI Flexure AISC Steel →

Vertical Distribution of Seismic Forces

Story	hx (ft)	wx (kip)	wx·hx^k	Cvx	Fx (kip)	Vx (kip)

Step-by-Step Solution

Preliminary calculation tool. Ss and S1 values must be obtained from USGS seismic design maps for the specific project site. Final design requires the full ASCE 7-22 text and review by a licensed PE.