ASCE 7-22 Wind: Chapter 27 Directional MWFRS for Partially Enclosed Warehouse

Technical NotesOpen StructSuite

Example

A Risk Category II warehouse is 100 ft long by 80 ft wide with a flat roof and mean roof height h = 28 ft. A large roll-up door on one long wall can create a partially enclosed condition. Ultimate design wind speed V = 115 mph, Exposure C, K_d = 0.85, K_e = 1.0, K_zt = 1.0. The building is classified as partially enclosed per Section 26.12; use GC_pi = ±0.55 per Table 26.13-1. For Chapter 27 Section 27.3.1, take the height of the highest opening for positive internal pressure as z = 22 ft above ground (typical large door head height). Use z = 28 ft for windward wall q_z for the windward surface at full height unless a smaller controlling strip is specified. Determine MWFRS design pressures using the Directional Procedure.

How StructSuite solves this

Select Chapter 27. Enter Risk Category II, V = 115 mph, Exposure C, K_d = 0.85, K_zt = 1.0, K_e = 1.0. Set enclosure to partially enclosed and GC_pi = 0.55. Step 4: h = 28 ft; Step 5: q_z. Step 6: 100×80 ft, flat roof, θ = 0°; Step 4 shows Roof angle = 0.00°; enter highest opening height z = 22 ft and windward z = 28 ft. Step 7: Equation 27.3-1 pressures and Section 27.1.5 minimum loads (16/8 psf for enclosed/partially enclosed). Step 8: Figure 27.3-8.

Steps

  1. Wind MWFRS procedure: Chapter 27 (Directional)

    Design consideration: Warehouses with large doors are often partially enclosed or require a rational analysis when the door is open; the selected classification must match the load case in the permit set. Chapter 27 Section 27.3.1 uses q_z at the height of the highest opening for positive internal pressure when partially enclosed—this can significantly increase net pressure on the roof and leeward wall compared to enclosed.

    In StructSuite: At the top of the wind module, above Step 1, select the Chapter 27 — Wind Loads on Buildings: Main Wind Force Resisting System (Directional Procedure) radio button (not Chapter 28 Envelope Procedure). This example uses ASCE 7-22 Chapter 27 Section 27.3.1 and Figure 27.3-1 for MWFRS pressures.

  2. Step 1: Determine risk category of building

    Design consideration: 115 mph with partially enclosed GC_pi amplifies net pressure changes versus ±0.18. Door and opening schedules should be consistent with the classification stated in the wind load calculation.

    In StructSuite: In Step 1, use the Risk Category dropdown to select I, II, III, or IV (e.g., II for offices, residential). In the Basic Wind Speed (mph) input box enter 115. Per ASCE 7-22 Section 26.2, Figure 26.5-1. If using address lookup, use the address search to auto-fill wind speed.

  3. Step 4: Velocity pressure exposure coefficient

    Design consideration: Flat roof and long span diaphragms: large plan dimensions increase total shear to the lateral system. Mean roof height 28 ft drives K_z in Exposure C; confirm door opening height and mean roof height are consistent with the architectural sections.

    In StructSuite: In Step 4, enter Mean Roof Height h (ft) and confirm Kh from Table 26.10-1 (this example uses h = 28 ft). Chapter 27 Directional lists Kz at each elevation z on the Step 4 blue summary. In Step 6, enter Building Length = 100 ft, Building Width = 80 ft, roof type, and roof angle θ (0.0° for this example). After θ is entered, the Step 4 accordion line includes Roof angle = …° or Roof angle = rise:run = …°.

  4. Step 3: Wind load parameters

    Design consideration: Exposure C with K_zt = 1.0 assumes flat terrain; confirm no escarpment within the approach distance. If K_zt > 1.0, velocity pressure increases at the site.

    In StructSuite: In Step 3, use the Exposure dropdown to select B, C, or D. If ground elevation > 1000 ft, use Table 26.9-1 for Ke. For topographic features (hills, ridges), use the Kzt section and enter parameters from ASCE 7-22 Figure 26.8-1. Kd = 0.85 for MWFRS is typical.

  5. Step 5: Velocity pressure at mean roof height

    Design consideration: Chapter 27 uses q_z at discrete heights; for partially enclosed internal pressure, the q at the height of the highest opening is critical. Compare Step 5 tabulated q_z at z = 22 ft and z = 28 ft to the values used in Step 7.

    In StructSuite: In Step 5, verify velocity pressure at mean roof height and, for Chapter 27, the listed qz at each height z (ft) per ASCE 7-22 Table 26.10-1 and Equation 26.10-1. For this example, mean roof height is 28 ft and basic wind speed V is 115 mph.

  6. Step 6: External pressure coefficients

    Design consideration: Enter the height of the highest opening (ft) and windward z (ft) in the Chapter 27 Step 6 inputs so internal pressure uses the correct q. Review wall and roof C_p for both orthogonal directions; large doors can change which wall is critical for shear and torsion.

    In StructSuite: In Step 6, confirm Building Length (ft) 100, Building Width (ft) 80, Mean Roof Height (ft) 28, roof type Flat, and roof angle 0.0 degrees. For Chapter 27, review Figure 27.3-1 external pressure coefficients C_p for each orthogonal wind direction (Part 1 and Part 2). If the building is partially enclosed, enter the height z for windward q_z (ft) and the height of the highest opening (ft) where shown for Section 27.3.1 internal pressure.

  7. Step 7: Calculate wind pressure, p, on each building surface

    Design consideration: Partially enclosed cases often govern net uplift and lateral load on the MWFRS. Check both positive and negative external pressure with ±GC_pi. Step 7 includes Section 27.1.5 minimum design wind loads (16 psf wall + 8 psf roof vertical projections) in addition to Equation 27.3-1. The building is treated as rigid (n₁ or f₁ > 1 Hz) with G = 0.85 per Section 26.11.1; if it were flexible, G_f would be required per Section 26.11.2 outside the tool. Use governing pressures for connections, bracing, and foundation overturning.

    In StructSuite: In Step 7, review design wind pressure p on each building surface per ASCE 7-22 Equation 27.3-1 and Section 27.3.1 with Figure 27.3-1 C_p. StructSuite uses G = 0.85 for a rigid building (n₁ ≥ 1 Hz) per Section 26.11.1; confirm rigidity or use G_f manually if n₁ < 1 Hz. Use governing surface pressures for MWFRS load combinations; account for both positive and negative external pressure with internal pressure (GC_pi) from Step 3. Review the Section 27.1.5 Minimum Design Wind Loads card (16 psf / 8 psf wall and roof vertical projections, or 16 psf × Af for open buildings; gable end wall for wind parallel to ridge).

  8. Step 8: Evaluate design wind load cases

    Design consideration: Figure 27.3-8 cases use the Step 7 wall pressures; partially enclosed q_i at the highest opening flows into both pressure columns. Compare Case 2 and Case 4 torsion rows to the building’s actual diaphragm and bracing layout—semi-rigid diaphragms may need equivalent loads per the standard. Use the maximum horizontal shear and roof uplift summaries and the detailed line-by-line block in Step 8 for the permit package (Chapter 27 directional cases, not Chapter 28 Envelope Procedure). Base shear adds sloped-roof horizontal to wall shear when θ ≥ 10° (see Step 8 text); walls still use f × (p_W − p_L) × B_normal × h with internal-pressure terms dropping in (p_W − p_L) for each ±GC_pi column. Flat roofs here omit the roof horizontal term; if the project switched to Chapter 28 for a low-rise retrofit, normal zone pressures and component resolution replace that Chapter 27 split—one procedure per sheet.

    In StructSuite: In Step 8, review MWFRS design wind load cases per ASCE 7-22 Section 27.3.5 and Figure 27.3-8 (Cases 1–4 and internal pressure ±GC_pi columns) after Step 7 pressures are established. Horizontal base shear is V_walls + V_roof: walls use f × (p_W − p_L) × B_normal × h (signed Equation 27.3-1); for sloped gable/hip and θ ≥ 10°, add roof horizontal along the axis normal to ridge as f × (p_rw − p_rl) × A_half × sin θ (A_half = L×(B/2)/cos θ, q_h, windward primary C_p); wind parallel to ridge uses V_x,roof = 0 (symmetric cancellation). Internal GC_pi cancels in (p_W − p_L) for global wall shear. Chapter 28 Envelope instead sums along-wind components of normal pressures on Figure 28.3-1 zones—use one MWFRS procedure per governing calculation, not both combined.

Live design (pre-filled)

The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.

Steps to Determine Wind Loads on MWFRS

ASCE 7-22 Tables 27.2-1, 28.2-1

User Note: Use Chapter 27 to determine wind pressures on the MWFRS of buildings with any general plan shape, building height, or roof geometry that matches the figures provided. These provisions use the traditional "all heights" method (Directional Procedure) by calculating wind pressures using specific wind pressure equations applicable to each building surface.

User Note: Use Chapter 28 to determine the wind pressure on the MWFRS of low-rise buildings that have a flat, gable, or hip roof. These provisions use the Envelope Procedure by calculating wind pressures from the specific equation applicable to each building surface. For building shapes and heights for which these provisions are applicable, this method generally yields the lowest wind pressure of all the analytical methods specified in this standard.

Figure 27.3-1 external pressure coefficients

Equation (27.3-1) for rigid and flexible buildings

Section 27.3.5 and Figure 27.3-8.