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In this example, we are going to calculate averaged force values, such as those applicable to structural sections in the design process based on WTG-Merkblatt-M3
This example belongs to Group 1 according to the Figure 2.2 in WTG-Merkblatt-M3 is:
- G2: Absolute values with medium accuracy requirements. The area of application can include parameters or preliminary studies when later investigations with higher accuracy are planned (e.g., wind tunnel examination of class G3).
- R2: Solitary, all relevant wind directions with sufficiently fine directional resolution.
- Z1: Statistical mean values, provided it concerns stationary flow processes where fluctuations (e.g., due to approaching flow turbulence) can be sufficiently captured by other measures.
- S1: Static effects. It is sufficient to represent the structural model with the necessary mechanical detail, but without mass and damping properties.
The dimension of the example shows in Figure 1, and also the input assumption is illustrates as Table 1:
In this example we will compare average wind force value in X-direction between EN 1991-1-4 and RWIND. Force coefficient cf,o for bridges sections can be obtained by Figure 8.3 in EN 1991-1-4:
Force in x-direction - Simplified Method
Where it has been assessed that a dynamic response procedure is not necessary, the wind force in the x-direction may be obtained using Expression (8.2) in EN 1991-1-4:
vb=30 m/s is the essential wind speed
C is the wind load factor. C=ce⋅cf,x=1.425×1.3=1.85 , where ce is the exposure factor given in 4.5 and cf,x is given in 8.3.1(1):
Aref,x=5 m2 is the reference area given in 8.3.1
ρ=1.225 kg/m3 is the density of air
The force results in RWIND and comparison to Eurocode
In RWIND the results of the total wind forces are available in the info tab of the edit model as shown in Figure 2 and Figure 3. The difference between critical wind direction scenario RWIDN (θ=0°) and Eurocode is about 5.36% (less than the criteria in WTG = 10%) which shows acceptable agreement:
