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ASCE 7-22 Tornado Loads (Chapter 32)

New in ASCE 7-22: Risk Category III and IV buildings in the tornado-prone region must be checked for tornado loads. q_zT = 0.00256·K_zTor·K_e·V_T² (Eq. 32.10-1 — no K_zt, no K_d); the tornado and wind results are compared, and the larger governs.

Site and building

Risk category

Basic wind speed V (mph)

Tornado speed V_T (mph, Ch. 32 maps)

Exposure

Mean roof height h (ft)

Ground elevation z_g (ft)

Enclosure (Table 32.13-1)

Rooftop equipment K_dT

Interpolate V_T between two effective-plan-area maps (log A_e)

A_e (ft²)

Map A₁ (ft²)

V_T at A₁

Map A₂ (ft²)

V_T at A₂

Results

Quantity	Value	Clause

Sources and verification

CoefficientsK_zTor, K_dT, G_T = 0.85, GC_piT, K_vT, K_e and the applicability limits are each confirmed in at least two free sources: FEMA/NIST Design Guide for New Tornado Load Requirements in ASCE 7-22 (2023, public domain), NCSEA Wind Engineering Committee Example Problems: Tornado Loads on Schools and Hospitals (2023), Florida Building Commission Tornado Loads – Impacts from ASCE 7-22 (2024), ICC Demystifying Loads Part 2 and the ICC tornado briefing (M. Levitan, 2023). ASCE 7-22 is cited by clause number only.

AnchorsThe engine reproduces the published examples within ±0.15 psf: FEMA/NIST Tulsa hospital (q_hT 29.3 psf, MWFRS roof uplift −35.8 psf, window zone 5 −58.6 psf, rooftop equipment 47.3 / 41.1 psf), NCSEA Oklahoma City hospital (K_e 0.96, q_hT 26.5 psf) and Evansville school (log-A_e interpolation 66.1 mph → exempt), Florida Tallahassee examples and ICC Springfield (roof zone 3 −58.7 psf). Known misprints in the sources are excluded from the tests.

Method choiceFor rooftop equipment the FEMA/NIST guide uses K_dT = 0.85 (Table 26.6-1 via Table 32.6-1), while the NCSEA hospital example uses 1.0. The tool lets you choose; the FEMA/NIST reading is the default.

ScopeV_T is read from the ASCE 7-22 tornado maps (ASCE 7 Hazard Tool). External coefficients C_p and (GC_p) come from Chapters 27–30 as for wind. Buildings designed to Chapter 32 are not storm shelters (ICC 500 / FEMA P-361).