Example
A warehouse in open terrain (Exposure C), 50 ft × 100 ft, 25 ft mean roof height. Basic wind speed 120 mph. Site on 2D ridge: hill height H=100 ft, Lh=200 ft, building at crest. Determine qh with Kzt. Exposure C and Kzt increase pressure vs suburban.
How StructSuite solves this
In StructSuite Wind Loads, Step 3: Select Exposure C (open terrain). Kzt: enable Table method, enter H = 100 ft, Lh = 200 ft, x, z, hill shape 2D Ridge, upwind/downwind. Step 4: Enter h = 25 ft and confirm Kh; after Step 6 geometry, Step 4 shows roof angle. Step 5: qh = 0.00256×Kh×Kzt×Ke×V². Exposure C yields higher Kh than B; Kzt at crest can increase pressure substantially.
Steps
- Step 1: Determine risk category of building
Design consideration: Warehouse Risk II. 120 mph—open terrain often in rural/farmland. Wind contours vary; open exposure can occur in buffer between suburban and coastal. Higher V and Exposure C compound.
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 120. 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 sets h and Kh; Step 6 sets L, B, θ. Step 4 accordion lists Kz at each z for Chapter 27 Directional. 25 ft height in Exposure C: Kh≈0.94 vs 0.70 in B—34% higher qh before Kzt.
In StructSuite: In Step 4, enter Mean Roof Height h (ft) and confirm Kh from Table 26.10-1 (this example uses h = 25 ft). Chapter 27 Directional lists Kz at each elevation z on the Step 4 blue summary. In Step 6, enter Building Length = 50 ft, Building Width = 100 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: C: open country, obstacles <30 ft. Kzt from Figure 26.8-1: H (hill height), Lh (horizontal), x (building position). Crest (x=0): Kzt max. 2D ridge vs 3D hill: different multipliers. H/Lh=0.5, x=0: Kzt can reach 2.0.
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×Kzt: at crest Kzt can greatly increase design pressure. Chapter 28 MWFRS Step 7 includes minimum design wind load cases per Section 27.1.5 / 28.3.6. Document H, Lh, x, shape on structural drawings. Computed envelope base shear uses along-wind summation per zone (StructSuite: windward F, leeward −F on walls; parallel sidewalls 0; leeward roof −F×sin θ). For Chapter 28, zone pressures from Figure 28.3-1 are normal to each surface; sloped roof contributions enter base shear through horizontal components of those normals, avoiding double-count with wall strips.
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.