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# Calculate Seismic Loads (ASCE 7-22)
> Calculate seismic design forces and equivalent lateral loads to ASCE 7-22 for US buildings. Finds SDC, spectral accelerations, base shear, and story forces.
Calculate seismic design forces and equivalent lateral loads to ASCE 7-22 for US buildings. Determines seismic design category, spectral accelerations, base shear, and story forces for equivalent lateral force procedure.
Easily determine seismic parameters and loads according to ASCE 7 using Calcs.com Seismic Analysis calculator.
## Method & scope
| Property | Detail |
| ------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | ASCE 7-22 |
| Regions | United States |
| Who it's for | US structural engineers, architects, and construction professionals running seismic analysis to ASCE 7-22. |
| What it helps with | Retrieve site parameters automatically via Project Details, or manually from the ASCE Hazard Tool. Outputs spectral accelerations, seismic design category, base shear, and equivalent lateral forces — all linkable into Wood Shear Wall and other calculators so seismic loads don't need re-entry. Keeps designs compliant with IBC 2024 and aligned with the snow and wind load calculators for end-to-end ASCE 7-22 workflows. |
| What it checks | Site-adjusted spectral accelerations (ASCE 7-22, Cl. 11.4), Seismic design category (SDC), Seismic base shear (ASCE 7-22, Cl. 12.8), Vertical distribution of seismic forces |
#### Calculation method
The Seismic Analysis (ASCE 7-22) calculator determines seismic design forces for US buildings using the Equivalent Lateral Force (ELF) procedure per ASCE 7-22 Chapter 12. It converts spectral acceleration parameters from the 2018 USGS National Seismic Hazard Model into a seismic base shear and distributes that force to each building story.
##### Site-adjusted spectral accelerations (ASCE 7-22, Cl. 11.4)
Starting from the mapped short-period acceleration (S\_s) and long-period acceleration (S\_1) from ASCE 7-22 Figure 22-1, the calculator applies site coefficients F\_a and F\_v to obtain the maximum considered earthquake (MCE\_R) spectral accelerations:
**S\_MS = F\_a × S\_s** (site-adjusted short period)
**S\_M1 = F\_v × S\_1** (site-adjusted long period)
Design spectral accelerations are two-thirds of the MCE\_R values:
**S\_DS = 2/3 × S\_MS**
**S\_D1 = 2/3 × S\_M1**
Note: ASCE 7-22 removed the Supplement 3 S\_M1 amplification that applied to Site Class D in ASCE 7-16 when S\_1 exceeded 0.2. The 2022 edition instead incorporates updated site amplification factors derived from the 2018 NSHM.
##### Seismic design category (SDC)
SDC is determined from ASCE 7-22 Tables 11.6-1 and 11.6-2 as the more severe of the category based on S\_DS and S\_D1, considering the building's Risk Category. Both tables are always evaluated.
##### Seismic base shear (ASCE 7-22, Cl. 12.8)
The seismic response coefficient C\_s is calculated from S\_DS, the response modification coefficient R, and the importance factor I\_e. It is checked against the S\_D1-based upper bound for long-period buildings and a minimum floor. Base shear:
**V = C\_s × W\_total**
Where W\_total is the effective seismic weight. The fundamental period T is either computed as the approximate period T\_a = C\_t × h\_n^x per ASCE 7-22 Table 12.8-2, or entered as a custom value, subject to the C\_u upper bound.
##### Vertical distribution of seismic forces
The base shear is distributed to each story level using the vertical distribution exponent k (1.0 for T ≤ 0.5 s, 2.0 for T ≥ 2.5 s, interpolated between):
**F\_x = C\_vx × V**, where **C\_vx = w\_x × h\_x^k / sum(w\_i × h\_i^k)**
The lateral load at each story and the cumulative shear are tabulated and can be exported for diaphragm and lateral system design.
##### Assumptions
The building is assumed to have no torsional irregularities. No height limit increases or structural system modifications are considered. The simplified design procedure per Cl. 12.14 is not used. Site Class F requires a site-specific response analysis and is not supported.
## How to use it
Open it from **Run calc** in the About this calculator panel above.
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
## Common questions
The calculator implements ASCE 7-22 seismic load provisions using the Equivalent Lateral Force (ELF) procedure from Chapter 12. It determines seismic design category (SDC), design spectral accelerations (SDS and SD1), the seismic base shear (V), and the vertical distribution of seismic forces to each story.
Key inputs are site coordinates or mapped spectral accelerations (SS and S1) from the 2018 USGS NSHM, site class (A through F per ASCE 7-22 Chapter 20), risk category (I through IV), seismic force-resisting system type, response modification coefficient (R), redundancy factor (rho), effective seismic weight (W), and building height or fundamental period.
Outputs include design spectral accelerations (SDS and SD1), seismic design category (SDC A through F), base shear (V = CsW), and the lateral force at each story level using the exponent k distribution. These forces can be directly applied to the structural system for shear wall and diaphragm design.
The ELF procedure applies to regular structures in SDC B and C, and to regular structures meeting the height and period limits in SDC D, E, and F per ASCE 7-22 Section 12.6. For irregular structures or those exceeding ELF applicability limits, modal response spectrum analysis or seismic response history analysis is required and is not covered by this calculator.
ASCE 7-22 uses the updated 2018 USGS National Seismic Hazard Model (NSHM), which changes mapped spectral accelerations in many areas compared to the 2014 NSHM used in ASCE 7-16. ASCE 7-22 also revised site class definitions in Chapter 20, replacing the old Vs30-based Site Class D split with a more refined classification. Use this calculator for projects subject to IBC 2024, and the ASCE 7-16 seismic analysis calculator for earlier code cycles.
The base shear and story forces from this calculator feed directly into shear wall and diaphragm design. You distribute the total base shear to the lateral force-resisting elements in proportion to their relative rigidity, then check each shear wall using the Wood Shear Wall (ASD) calculator or equivalent. Seismic story forces can also be entered as lateral loads in column and moment frame calculators.
## Next steps
Worked example: seismic design category, spectral accelerations, base shear and story forces to ASCE 7-16 with the equivalent lateral force procedure.
Complete list of Calcs.com design calculators available for United States projects (AISC, ACI, NDS, ASCE 7, IBC, and related standards).
Calculate MWFRS and components and cladding wind pressures to ASCE 7-22 for low-rise buildings, with code references on every output.
Get balanced and unbalanced snow loads for sloped and flat roofs to ASCE 7-22 Chapter 7, including drift on lower roofs. Current edition for IBC 2024.
