ASCE 7-22 Wind Loads on MWFRS (StructSuite Wind Module)
Reference: ASCE/SEI 7-22, Chapters 26–28, Chapter 2 (load combinations).
Technical version: 2.2 (April 2026) — aligned with WindWizardApp: procedure selector at top, Equation (26.10-1) for q with no Kd (Kd enters p in Equations (27.3-1) / (28.3-1)), address / ASCE Hazard Tool V lookup, and Step 8 only for Chapter 27 (Figure 27.3-8 block is hidden for Chapter 28). On-screen step titles for Steps 1–8 follow content/wizard-labels/wind.json (risk category through design wind load cases).
1. Procedure selection: Chapter 27 vs Chapter 28
At the top of the wind module (before Step 1), choose one radio option:
| Procedure | When to use (summary) |
|---|---|
| Chapter 27 — Directional Procedure | Traditional “all heights” method: Figure 27.3-1 C_p and Section 27.3.1 (Equation 27.3-1). Use when the project calls for this procedure, or when Chapter 28 does not apply (e.g. mean roof height h > 60 ft, or h > min(L, B), or geometry outside Chapter 28 flat/gable/hip assumptions). |
| Chapter 28 — Envelope Procedure | Low-rise buildings: h ≤ 60 ft, h ≤ min(L, B), flat, gable, or hip roof. Uses GC_pf zones (Figure 28.3-1 / 28.3-2), Equation 28.3-1, and Section 28.3.2 load cases. The in-app user note states this method often yields the lowest pressures among analytical MWFRS methods where it applies. |
Do not mix Chapter 28 zone GC_pf pressures with Chapter 27 C_p / Equation (27.3-1) on the same cover sheet unless the governing code path explicitly allows it.
2. Wizard steps (shared numbering; content differs by procedure)
On-screen accordion titles use Table 27.2-1 / 28.2-1-style wording (WindWizardApp). Step 6’s main line reads “Determine external pressure coefficient, (GC_pf)” for both procedures; the blue substep differs: Chapter 27 → Figure 27.3-1 external pressure coefficients; Chapter 28 → Section 28.3.2 load-case context for flat/gable roofs. Design-example titles come from content/wizard-labels/wind.json (slightly shorter labels).
| Step | Role (both procedures) |
|---|---|
| 1 | Risk category (Table 1.5-1). |
| 2 | Basic wind speed V (manual entry or address search + ASCE Hazard Tool). Optional override of API V. |
| 3 | Wind load parameters: K_d (Table 26.6-1), exposure B/C/D, K_zt (direct factor or hill parameters per Figure 26.8-1), K_e (Table 26.9-1), enclosure / GC_pi (Sections 26.12–26.13) including optional calculated enclosure from opening ratios. |
| 4 | Mean roof height h and velocity pressure exposure coefficient K_z or K_h (Table 26.10-1). Chapter 27: accordion lines can list K_z at each listed height z. After roof angle θ is entered in Step 6, Step 4 summaries can show roof angle in degrees or rise:run. |
| 5 | Velocity pressure q_h (Equation 26.10-1): q = 0.00256 K_z K_zt K_e V² — K_d is not included in q (it applies when forming p in Step 7). Chapter 27: also lists q_z at elevations z used for the directional run. Chapter 28: q_h feeds envelope zone pressures after Step 6. |
| 6 | Building length L, width B, roof type, roof angle θ, and external pressure data for the selected procedure. Chapter 27: Figure 27.3-1 C_p (two orthogonal plan directions); optional z for windward q_z; for partially enclosed, height of highest opening for internal pressure. Chapter 28: zone dimension a (Table 28.2-1), GC_pf from Figures 28.3-1 / 28.3-2, and Section 28.3.2 torsional exception attestation when applicable. |
| 7 | Chapter 27: Equation (27.3-1) design wind pressure p on each surface; Section 27.1.5 minimum design wind loads card (16 psf / 8 psf wall and roof projections, open-building rules, etc.). Chapter 28: Equation (28.3-1) pressures by zone and load case; Section 28.3.2 load-case tables and diagrams; comparison to Section 27.1.5 / 28.3.6 minimums where the app shows governing base shear and uplift (summaries use strength-level W and allowable-stress 0.6W style labels). |
| 8 | Chapter 27 only (this step is not rendered for Chapter 28): Section 27.3.5 and Figure 27.3-8 MWFRS cases (Cases 1–4), torsion, base shear / uplift summaries (V = V_walls + V_roof,horizontal where applicable; same W / 0.6W labeling pattern as Chapter 28 summaries). |
| (diagram) | Interactive Building Diagram — appears when wind results exist and the diagram step is enabled in the build (after Step 7 for Chapter 28; after Step 8 for Chapter 27). Product note: this accordion may be temporarily hidden in the UI while the experience is refined; calculation steps and results above it are unchanged. |
Until Steps 1–6 and q_h are complete, the module shows red instructional lines under later steps; when complete, blue accordion summaries show computed values—same pattern throughout.
Chapter 28 validation: If h > 60 ft or h > min(L, B) (or other envelope limits), the app surfaces errors for the Envelope procedure; use Chapter 27 instead when those limits are exceeded.
3. Gust-effect factor G (Equation 27.3-1) — Chapter 27 Step 7
Equation (27.3-1) uses G from Section 26.11.
- Rigid: n₁ ≥ 1 Hz; Section 26.11.1 allows G = 0.85.
- Flexible: n₁ < 1 Hz requires G_f per Section 26.11.2.
StructSuite assumption: Chapter 27 Step 7 uses G = 0.85 (rigid building). If n₁ < 1 Hz, compute G_f outside the tool and substitute into Equation (27.3-1) for governing design.
Rigid vs. flexible (wording for calc packages): The tool treats the building as rigid (n₁ > 1 Hz, same sense as f₁ > 1 Hz in many references). If the structure were flexible, Gf would be required per Section 26.11.2 instead of G = 0.85.
4. Section 27.3.5 and Figure 27.3-8 (Chapter 27 Step 8)
Figure 27.3-8 defines orthogonal MWFRS cases used with p from Section 27.3.1. The Step 8 accordion implements that figure for Chapter 27 only—Chapter 28 envelope load cases stay in Steps 6–7, not Figure 27.3-8.
Horizontal shear summaries use V = V_walls + V_roof,horizontal: V_walls = f × (p_W − p_L) × B_normal × h (signed Equation (27.3-1) wall pressures; internal GC_pi cancels in p_W − p_L). For sloped gable or hip roofs (θ ≥ 10°, not flat), the app adds V_y,roof = f × (p_rw − p_rl) × A_half × sin θ with A_half = L (B/2) / cos θ (sloped area of one roof half: ridge length × half-span along the slope), q_h, and windward primary roof C_p from Figure 27.3-1 (wind normal to ridge / along y when ridge is along L). V_x,roof = 0 (symmetric opposing slopes cancel for wind parallel to ridge). Flat roofs or θ < 10° use no roof horizontal term in this summary (parallel-to-ridge strip rules apply per the figure). Torsion M_z rows still use the wall (p_W − p_L) B basis only. Roof uplift follows Note 2 (|p| × L × B where applicable). Detailed 3D or FEA models may differ.
Transparency: Global roof shear uses the windward primary C_p only—localized windward roof zones in Figure 27.3-1 are not subdivided for this horizontal drag term. Hip roofs use the same gable-equivalent A_half (slightly conservative on sloped area). M_z from walls-only torsion is consistent with symmetric plans where net roof torque about the vertical is often negligible.
5. Chapter 28 Envelope (brief)
- Pressures: Equation (28.3-1) with GC_pf from Figures 28.3-1 and 28.3-2 where torsional cases apply.
- Load Cases 1–4 and optional torsional cases follow Section 28.3.2; user attestation when a torsional exception applies (Step 6).
- Base shear in Step 7 is the sum of along-wind horizontal components from each zone: windward walls use F; leeward walls use −F (so leeward suction adds to shear, consistent with Chapter 27 p_W − p_L); long sidewalls when wind is parallel to the ridge contribute 0 along-wind; leeward roof halves (zones 3, 3E, 3T) use −F sin θ along-wind so roof suction does not subtract from shear.
- Minimum MWFRS wind loads: Section 27.1.5 / 28.3.6; the app compares computed and minimum base shear where shown.
Normal pressure vs. base shear (Chapter 28): In Chapter 28, design pressures from Equation (28.3-1) act normal to each surface using the zoned areas from Figure 28.3-1 (and 28.3-2 where torsional cases apply). Normal forces on sloped roof zones are then resolved into horizontal and vertical components for each load case. That path rolls the roof’s along-wind contribution into the zone summation and avoids double-counting roof shear against wall strips. Chapter 27 uses a different but consistent split: wall base shear from (p_W − p_L) on the windward/leeward vertical faces and, for qualifying sloped gable/hip roofs, an explicit roof horizontal term from windward/leeward roof C_p—do not mix the two procedures on one cover sheet.
Minimum load vs. analytical pressures: Section 27.1.5 / 28.3.6 minimum MWFRS wind load is a floor on global effects (16 psf / 8 psf on defined vertical projections for enclosed buildings); it does not replace zone p for cladding, components, or local connection design.
6. Cross-references (do not confuse chapters)
- Section 28.3.1.1 (combined GC_pf) applies to Chapter 28, not to Chapter 27 C_p and G in Equation (27.3-1).
- Section 28.3.2 (envelope load cases) is not the same as Figure 27.3-8 cases under Chapter 27.
Document the governing chapter on the calculation cover sheet.
7. Related design examples and notes
StructSuite includes Chapter 27 directional examples (e.g. gable roof, tall building over 60 ft, partially enclosed warehouse) and Chapter 28 envelope examples. Examples reference content/module-steps/wind.json and content/wizard-labels/wind.json where applicable. Seismic ELF wizard (ASCE 7-22 Ch. 12): StructSuite seismic loads — ELF wizard (ASCE 7-22). Chapter 27 base shear hand check: How to Calculate MWFRS Wind Base Shear….