Seismic Loads module
Free Seismic Load and Base Shear Calculator — ASCE 7-22 Equivalent Lateral Force Procedure
Calculate seismic base shear and story forces per ASCE 7-22 Chapter 12 (Equivalent Lateral Force). Site class and spectral parameters, risk category and importance factor, seismic force-resisting system (R, Cd, Ω0), period, response coefficient Cs, base shear, the vertical distribution of story forces with story shears and overturning moments, and diaphragm design forces (Fpx).
Free to use with no sign-up: the calculator runs in full in the browser with no account, no trial and no feature limits, and the full detailed calculation is shown on screen, step by step, with the code sections and tables it draws on, so it can be checked by hand. A free account keeps one project in the cloud; unlimited cloud projects and printing the report to PDF are Pro features.
What the calculator includes
- ASCE 7-22 tables to pick from, in the code's own layout: Site Class (Table 20.2-1), Risk Category and Ie (Tables 1.5-1 and 1.5-2), the Seismic Design Category (Tables 11.6-1 and 11.6-2 with the §11.6 exception) and the full Table 12.2-1 in lettered groups with the project's SDC column highlighted.
- Table 12.2-1 sets R, Ω0 and Cd on a click, flags a system Not Permitted in the project's SDC, warns when hn exceeds the height limit, offers the footnote b reduction of Ω0 for flexible diaphragms, and shows footnotes a to q in full.
- The period by Ct·hnx from Table 12.8-2, by 0.1N with its eligibility checked live, by the Cw shear-wall method, or typed directly and capped at Cu·Ta, with a control-period card placing T on the design spectrum.
- Cs from Eq. 12.8-3 with the 12.8-4 to 12.8-7 limits and the governing one named, the §12.8.1.3 cap as a seven-criteria checklist (five checked automatically), and a design-spectrum chart with the project's T marked.
- Base shear V, story forces Fx with Cvx and the exponent k, story shears Vx and overturning moments Mx, plus diaphragm design forces Fpx per §12.10.1.1 with the 0.2 and 0.4·SDS·Ie·wpx bounds, every row opening to its substitutions.
- Four force diagrams — story forces, story shear, overturning moment and diaphragm forces — with the values labelled and a switch between the strength level E and the allowable level 0.7E; everything is reported at both levels.
In every StructSuite module
- The code clause behind a value is quoted verbatim beside it from a blue book icon — NDS 2024, SDPWS 2021, AISC 360-22, ACI 318-25, ASCE 7-22 and the 2024 IBC, FEMA P-750 and the I-joist manufacturer's technical bulletins — so the standard does not have to be opened to check it.
- A missing input stops the calculation rather than being filled in silently, and judgment choices start unselected.
- Where a limit applies it is checked as you type: beam RB and column ℓe/d, steel Lc/r, rebar ratios and spacing, fy and f′c.
- Every module prints into one calculation report (Pro) with a cover sheet, a table of contents with measured page numbers and a verification link a plan checker opens without an account.
Worked examples and guides for this module
Each guide works the method end to end on the numbers the engine produces. The sample calculation report (PDF) is a complete StructSuite report printed from the sample project — open it without an account.
Frequently asked questions
Which procedure does the seismic load calculator use?
The equivalent lateral force procedure of ASCE 7-22 Chapter 12. You enter the site class and mapped spectral parameters, the risk category, the seismic force-resisting system (R, Cd, Ω0) and the story weights; it returns SDS and SD1, the Seismic Design Category, the approximate period Ta, the response coefficient Cs, the base shear V, the story forces Fx and the diaphragm design forces Fpx.
Can I check the numbers by hand?
Yes. Every step is shown on screen with the equation and the table it comes from, and the worked example guide linked above runs the same procedure on a two-story wood house with every number computed by this calculator.
Does it distribute the story shear to the shear walls?
No. It gives the story forces Fx, the story shears Vx, the overturning moments Mx and the diaphragm forces Fpx at every level, at the strength level E and at 0.7E. Distributing a story force to the individual shear walls, and the collector forces, happen in the shear wall calculator, where the story force is entered.
Is the seismic loads calculator free?
Yes. Free to use with no sign-up: the calculator runs in full in the browser with no account, no trial and no feature limits, and the full detailed calculation is shown on screen, step by step, with the code sections and tables it draws on, so it can be checked by hand. A free account keeps one project in the cloud; unlimited cloud projects and printing the report to PDF are Pro features.