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# Cladding Pressure Calculation Using CFD (AS/NZ 1170.2: 2021)

Figure 1. Wind turbulent flow around a high-rise building analysed by CFD

AS1170.2 is an Australian standard that provides guidelines for the design of buildings and structures for their structural stability in wind. Part of this standard provides information about wind loads on external cladding and the calculation of wind pressure coefficients.

According to AS1170.2, the design wind pressure for cladding can be calculated using the following formula:

P = q * G * Cp

where:

P = design wind pressure on cladding (Pa)

q = dynamic pressure (Pa)

G = gust response factor

Cp = pressure coefficient

The dynamic pressure, q, is calculated as:

q = 0.613 * K * V^2

where:

K = terrain, topography and shielding factor

V = basic wind speed (m/s)

The gust response factor, G, depends on the structure's natural frequency and damping ratio and can be calculated using the equations provided in the standard.

The pressure coefficient, Cp, is determined by the cladding type, its location on the building, and other factors. AS1170.2 provides tables and equations for calculating the pressure coefficient for different types of cladding, including sheet cladding, profiled sheet cladding, and curtain wall systems.

It is important to follow the guidelines provided by AS1170.2 for cladding pressure to ensure that buildings and structures are designed to withstand the expected wind loads and remain safe during extreme weather events.

CFD simulations can be used to calculate the cladding pressure using the guidelines provided in AS1170.2.

Computational Fluid Dynamics (CFD) is a powerful tool that can be used to simulate and analyse wind flow around buildings and other structures. CFD can be very helpful in wind loading calculations as it provides a more detailed and accurate understanding of wind behaviour compared to traditional wind tunnel testing.

Figure 2. High wind loading (pressure) on a typical mid-rise building calculated by CFD

1. Create a 3D model of the building and surrounding environment in CFD software. The model should include the building geometry, surrounding terrain, nearby buildings, and vegetation.

2. Define the wind conditions, including wind speed, direction, turbulence intensity, and reference height, based on AS1170.2. These parameters are used to simulate the wind flow around the building.

3. Define the properties of the cladding materials, such as thickness, roughness, and orientation, as well as the location and size of openings, such as windows and doors.

4. Run a CFD simulation to obtain the wind flow pattern around the building and the pressure distribution on the cladding. This can be done using a steady-state or transient analysis method.

5. Calculate the cladding pressure using the pressure distribution obtained from the CFD simulation. The cladding pressure can be calculated by integrating the pressure distribution over the area of the cladding.

6. Compare the calculated cladding pressure with the design wind pressure specified in AS1170.2. If the calculated pressure is higher than the design pressure, the cladding system may need to be modified or additional support may be required.

7. Evaluate the safety of the building under different wind conditions using the wind loading results obtained from the CFD simulation. The wind loading results can be used to verify the structural stability of the building and ensure that it can withstand the expected wind loads.

It is important to note that CFD simulations require significant computational resources and expertise to perform, and the results should be validated against experimental data to ensure accuracy. Additionally, the CFD simulation should be performed by an experienced engineer who is familiar with AS1170.2 and can interpret the results correctly.