Example
A Risk Category II office building is 80 ft × 60 ft in plan with 30 ft mean roof height. Basic wind speed 115 mph, Exposure B. Determine velocity pressure qh for MWFRS design per ASCE 7-22 Chapter 26 and Table 26.10-1.
How StructSuite solves this
In StructSuite Wind Loads, complete Steps 1–3 (risk, V, Kd, exposure, Kzt, Ke, enclosure, GC_pi). In Step 4, enter Mean Roof Height h = 30 ft and confirm Kh from Table 26.10-1; Step 4 blue summary also shows roof angle after you enter θ in Step 6 (enter flat roof, θ = 0°). Step 5 displays qh from Equation 26.10-1. For full MWFRS zone pressures, select Chapter 27 or Chapter 28 and complete Steps 6–7.
Steps
- Step 1: Determine risk category of building
Design consideration: V drives q ∝ V²—115 mph vs 130 mph = 28% higher pressure. Risk Category affects importance factor. Coastal (130–170 mph) and hurricane (180 mph) require robust connections. Inland 90–115 mph typical.
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.
- Step 4: Velocity pressure exposure coefficient
Design consideration: Step 4: Enter h and confirm Kh from Table 26.10-1; Chapter 27 Directional also lists Kz at listed heights z. Step 6: Enter L, B, roof type, and θ; then Step 4 accordion shows Roof angle = …°. Mean roof height h sets Kh: higher h = higher Kh. 30 ft in Exposure B: Kh≈0.70.
In StructSuite: In Step 4, enter Mean Roof Height h (ft) and confirm Kh from Table 26.10-1 (this example uses h = 30 ft). Chapter 27 Directional lists Kz at each elevation z on the Step 4 blue summary. In Step 6, enter Building Length = 80 ft, Building Width = 60 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 = …°.
- Step 3: Wind load parameters
Design consideration: Exposure B (suburban): Kh lower. C (open): ~30% higher qh than B. D (waterfront): highest. Site within 1500 ft of open water triggers D. Kzt: ridge/escarpment can double pressure at crest. Ke for elevation >1000 ft.
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.
- Step 5: Velocity pressure at mean roof height
Design consideration: qh = 0.00256×Kh×Kzt×Ke×V². qh multiplies pressure coefficients (GC_pf, GC_pi) in the envelope procedure. Chapter 28 Step 7 adds Minimum Design Wind Loads per Section 27.1.5 / 28.3.6 when MWFRS is complete. When you continue to Chapter 28, load-case base shear is the sum of along-wind horizontal zone forces (leeward wall/roof suction adds; sidewalls parallel to wind contribute zero along-wind). Those horizontal pieces come from resolving normal design pressures on Figure 28.3-1 roof and wall zones, not from stacking an unrelated Chapter 27 roof strip on the same envelope result.
In StructSuite: In Step 5, velocity pressure qh is computed from ASCE 7-22 Equation 26.10-1. For Chapter 28 Envelope, continue to Step 6 for zone dimension a and GCpf from Figure 28.3-1; Step 7 shows zone pressures, load cases, and Minimum Design Wind Loads per Section 27.1.5 and 28.3.6 when applicable. For Chapter 27 Directional, Step 5 lists qz at each z; then Step 6–8 follow Figure 27.3-1 and Section 27.3.1.
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.