Quick answer The height profile of wind speed is Vz=V·(z/10)^α, and the velocity pressure is qz=½ρVz² (in ASCE 7, qz=0.613·Kz·Kzt·Kd·V²). The design wind pressure is p=qz·G·Cf (gust factor G≈0.85, force coefficient Cf).
Set basic wind speed, building dimensions, and terrain category to instantly compute design wind pressure, base shear, and overturning moment. Visualize the wind velocity profile and building facade pressure distribution in real time.
Design Parameters
Code
Terrain Category
Basic Wind Speed V
m/s
Building Height H
m
Width B (along wind)
m
Depth D
m
Results Summary
Results
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Windward Pressure p_w (kPa)
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Leeward Pressure p_l (kPa)
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Roof Pressure p_r (kPa)
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Base Shear V_b (kN)
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Overturning Moment M_ot (kN·m)
Wind Flow & Pressure on Building (Live)
Profile
Theory & Key Formulas
Power law: $V_z = V \cdot (z/10)^\alpha$
Velocity pressure: $q_z = \tfrac{1}{2}\rho V_z^2$
Design pressure: $p = q_z \cdot G \cdot C_f$
Gust factor $G = 0.85$ (ASCE 7)
What is Wind Load Calculation?
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What exactly is the "Terrain Category" in this simulator? Why does it matter if I'm just putting in a wind speed?
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Great question! Basically, wind doesn't blow at the same speed at all heights. Over a smooth, open field, it accelerates quickly with height. Over a dense city with skyscrapers, the ground-level wind is much slower and takes longer to speed up. The Terrain Category in the simulator controls the exponent $\alpha$ in the power law that models this. Try switching from "Open Country" to "Dense Urban" and watch how the calculated wind pressure changes, especially near the base of your building.
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Wait, really? So the wind speed at the top of my building is different from the "Basic Wind Speed" I input? How does that work?
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Exactly! The "Basic Wind Speed V" you enter is a reference speed, typically defined at 10 meters (about 33 feet) above ground in open terrain. The simulator then calculates the speed at every height $z$ on your building using the power law. For instance, a 50 m/s reference speed in open terrain ($\alpha \approx 0.10$) might only be 35 m/s at the base of a dense urban building. That's why the "Building Height H" slider is so crucial—it directly changes the maximum wind speed your structure sees.
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Okay, I see the velocity pressure and design pressure formulas. But what's the Gust Factor "G", and why is it always 0.85 here? That seems like a magic number.
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In practice, it's a simplification for this tool. The Gust Factor accounts for the fact that wind isn't steady; it has turbulent gusts that create higher short-term pressures. ASCE 7 uses $G=0.85$ for rigid buildings (like most steel/concrete frames) because their natural frequency is high enough that they don't dynamically amplify these gusts much. For very flexible structures (like tall, slender towers), a more complex calculation is needed. The simulator uses the 0.85 factor to give you the design pressure used for checking cladding and main wind force resisting systems.
Physical Model & Key Equations
The core model describes how wind speed increases with height due to the frictional drag of the Earth's surface, known as the atmospheric boundary layer. The power law is a standard engineering approximation.
$$V_z = V \cdot \left(\frac{z}{10}\right)^\alpha$$
$V_z$ = Wind speed at height $z$ (m/s) $V$ = Basic wind speed at reference height (10m) (m/s) $z$ = Height above ground (m) $\alpha$ = Power law exponent, set by the Terrain Category (e.g., 0.10 for open country, 0.30 for dense urban)
The velocity pressure represents the kinetic energy of the wind per unit volume. This is then converted into a design pressure acting on the building surface, incorporating a gust factor and a pressure coefficient that depends on the building's shape.
$$q_z = \frac{1}{2}\rho V_z^2 \quad \text{and} \quad p = q_z \cdot G \cdot C_f$$
$q_z$ = Velocity pressure at height $z$ (Pa or psf) $\rho$ = Air density (approx. 1.225 kg/m³ or 0.00238 slugs/ft³) $p$ = Design wind pressure (Pa or psf) $G$ = Gust effect factor (0.85 for rigid structures per ASCE 7) $C_f$ = Force coefficient, dependent on building Width B and Depth D (related to its aerodynamic shape)
Real-World Applications
High-Rise Building Design: This calculation is fundamental for determining the lateral wind force that the building's core and moment frames must resist. Engineers use the resulting shear and moment to size columns, braces, and connections. For instance, the twisting moment on a slender skyscraper is critically assessed using pressures derived from these formulas.
Cladding and Curtain Wall Design: The local design pressure $p$ directly dictates the required strength of windows, exterior panels, and their attachments. A common case is specifying the glass thickness and mullion size for a 50-story office tower based on the highest pressures at the corners and top of the building.
Industrial Structure Assessment: Silos, chimneys, and exposed pipe racks are analyzed using this methodology. The "Terrain Category" is especially important for a refinery in an open coastal area versus one in a dense industrial complex, as the wind profile changes drastically.
Code Compliance and Permitting: Before construction begins, structural calculations submitted for a building permit must demonstrate compliance with ASCE 7 wind load provisions. This simulator illustrates the first principles behind those mandatory calculations, showing how the code parameters interact.
Common Misunderstandings and Points of Note
First, are you mistaking the "Basic Wind Speed V" for the actual wind speed the building receives? This is merely the value at a height of 10m over flat, open terrain. If your actual site is in an urban area, you need to determine the vertical distribution using the power law and further consider the "Adjacent Building Influence Factor" due to surrounding structures. For example, if there is a tall building next door, a building on the leeward side experiences a "wind shelter effect" where the wind weakens. Conversely, "channeling effects" where wind accelerates can occur at building corners or in narrow passages between buildings. The simulator assumes standard shapes, so special site conditions require separate consideration.
Next, the selection of the "Terrain Category" is often taken too lightly. This is one of the most critical parameters determining the wind profile. For instance, starting from the same basic wind speed, the wind speed at 100m height can differ by 10-20% between a "city center" and an "open flat terrain". Use tools like Google Earth to view your site from above and objectively judge which category applies to the area within approximately 500m to 1km.
Finally, do not take the calculated "Base Shear Force" or "Overturning Moment" at face value. This tool fundamentally calculates for the "principal wind direction," where wind strikes one face of the building perpendicularly. However, actual storm winds change direction. In structural design, "wind direction-dependent calculations," which consider the building being attacked from all directions and pick up the most critical case, are essential. The correct way to use this simulator's results is for understanding representative values for a specific direction and for sensitivity analysis of how parameters affect the results.
Enter the basic wind speed in m/s using the velocity slider (typical range 25–50 m/s for design storms; ASCE 7 uses 3-second gust speed).
Set building height in meters and width in meters using the dimension sliders to define the exposed rectangular profile.
Results update instantly: windward pressure p_w, leeward pressure p_l, roof suction p_r, base shear V_b, and overturning moment M_ot are computed with fixed coefficients (Cf = +0.8 / −0.5 / −0.7, gust factor G = 0.85) and the power-law wind profile.
Worked Example
A 15 m tall, 12 m wide industrial warehouse in open terrain (α = 0.10) with a basic wind speed of 40 m/s. Wind speed at roof height: 40 × (15/10)^0.10 ≈ 41.7 m/s, so velocity pressure q_H = 0.5 × 1.225 × 41.7² ≈ 1,063 Pa. Windward pressure: p_w = 1063 × 0.85 × 0.8 ≈ +0.72 kPa (compression). Leeward: p_l = 1063 × 0.85 × (−0.5) ≈ −0.45 kPa (suction). Roof suction: p_r ≈ −0.63 kPa. Integrating the pressure over the 12 m width gives base shear V_b ≈ 176 kN and overturning moment M_ot ≈ 1,441 kN·m, which sizes the foundation tie-downs.
Standards & Assumptions
Standard / formula: ASCE 7 velocity pressure (SI) \(q_z = 0.613\,K_z K_{zt} K_d V^2\) [N/m²]. This tool uses \(q_z=\tfrac12\rho V_z^2\) (ρ=1.225 → 0.5ρ=0.613), design pressure \(p = q_z\,G\,C_f\), gust factor G=0.85, and the power-law profile \(V_z = V(z/10)^\alpha\).
Assumptions: Exposure, topographic and directionality factors are simplified to \(K_z=K_{zt}=K_d=1\). Pressure coefficients are constant (windward +0.8 / leeward −0.5 / roof −0.7). Base shear and overturning moment use numerical integration over 20 building layers. The code switch (ASCE 7 / Japan Building Standard Law) changes only the on-figure badge; the equations are the common simplified form.
Scope & limits: For single-direction, standard rectangular-prism estimates. Resonant/aeroelastic effects (H>90 m class), neighbouring-building interference, openings, local cladding pressures and worst-case directional analysis are not included. Real design requires each code's full factor set, wind-tunnel testing and dynamic analysis.
Practical Notes
Terrain category affects velocity pressure: open terrain (Category B) and rougher urban areas (Category D) differ by ~25%; ensure correct classification per ASCE 7 Table 26.7-1.
Roof suction magnitude often governs fastener spacing and sheathing capacity; pressures exceed windward loads at eaves and parapets.
Base shear and moment scale with tributary area; L-shaped or partial-height screening reduces exposed width significantly.
Gust effect factor G_f ranges 0.85–1.15; rigid structures (f < 1 Hz) use 0.85, flexible cantilevered signs use higher values.