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ASCE 7-22ASCE 7-16

Seismic Analysis (ASCE 7-22)

US structural engineers determining seismic design category, spectral accelerations, base shear, and story forces to ASCE 7-22, the current edition under IBC 2024. Results feed directly into shear wall and diaphragm design downstream. For projects under IBC 2021 or earlier, use the ASCE 7-16 version instead.

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What it calculates

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.

Code standards

  • ASCE 7-22

How it calculates

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.

Related calculators

Seismic Analysis (ASCE 7-16)→Wind Loads (ASCE 7-22)→Snow Loads (ASCE 7-22)→Wood Shear Wall (ASD)→

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Frequently asked questions

What design standard does this calculator follow?
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.
What are the key inputs?
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.
What does the calculator output?
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.
Can I use this for irregular or taller buildings?
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.
How does ASCE 7-22 differ from ASCE 7-16 for seismic analysis?
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.
How do I use seismic forces in shear wall design after this calculator?
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.

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