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🛡️How We Automatically Calculate Shielding Factors

Eurocode allows for reducing wind on ancillaries by adjusting the Ka factor. In this page we go through how Shapemaker automatically calculates the shielding factors for all ancillaries.

The automatic shielding is a powerful feature in Shapemaker that reduces the wind loads on ancillaries when they are positioned behind one another. When ancillaries are clustered closely, those located behind others experience reduced wind exposure. This feature calculates the reductions automatically, helping users achieve more accurate and efficient tower analyses.

Shapemaker uses the method presented in TIA-222-I, Section 2, Figure 2-13: Shielding Limitations and automatically finds the effect of shielding for each ancillary and then calculates the shielding factors. The shielding factors are calculated in each direction and for each ancillary, considering their size and position in space.

The examples below illustrate how shielding is automatically applied in simple arrangements. Shapemaker can handle complex ancillary configurations, including multiple antennas, equipment, and supporting steel mounts, with wind from any direction. In such dense arrangements, it automatically evaluates the potential shielding effects for each ancillary. However, if the exact shielding impact on a specific ancillary cannot be clearly determined—due to excessive overlap or uncertainty in spatial relationships—the most conservative applicable shielding factor already calculated is used. This ensures safety without overstating the shielding effect.

Example 1

Small antenna/equipment behind large antenna

Ancillary

Ka

Comment

A1

1.0

No shielding.

A2

0.0

The antenna is completely shielded behind A1, because it is located within 2x widths (756mm).

A3

0.5

The antenna is partially shielded by A1. Linear interpolation is used to calculate the shielding factor, considering the minimum shielding effect as Ka=1 (no shielding) and maximum as Ka=0 (complete shielding). See calculation below.

Shielding Factor Calculation:

KA3=1130−7561−0÷(1512−756)+0=0.5K_{A_3} = \frac{1130 - 756}{1 - 0} \div (1512 - 756) + 0 = 0.5

Shapemaker report shielding factor values:

Example 2

Large antenna behind small antenna/equipment

Ancillary

Ka

Comment

A1

0.84

Partially shielded by the A2 RRU. A1 is in the 100% shielding area, but the area of A2 is smaller than the area of A1. Therefore, the shielding factor is calculated considering antennas' proportions, 1 -A2/A1. See calculation below.

A2

1.0

No shielding.

Shielding Factor Calculation:

KA1=1−AreaA2AreaA1=0.84K_{A_1} = 1 - \frac{\text{Area}_{A_2}}{\text{Area}_{A_1}} = 0.84

Shapemaker report shielding factor values

Example 3

Large antenna behind small antenna and in partial shielding zone

Ancillary

Ka

Comment

A1

0.92

The A1 antenna is located within the partial shielding zone of A2. The maximum shielding effect A2 can have on A1 is 1 -A2/A1 and this would be valid if A1 is located within 100% shielding zone (less than 684mm away). The minimum shielding effect would be if A1 is located outside of the partial shielding zone, which is more than 1368mm away. Linear interpolation is used to find the shielding effect considering the maximum and minimum effects.

A2

1.0

No shielding.

Shielding Factor Calculation:

Maximum shielding effect: 1−A2A1=0.841 - \frac{A_2}{A_1} = 0.84

Minimum shielding effect: 1

KA1=((1030−684)×(1−0.844)1368−684)+0.844=0.922K_{A_1} = \left( \frac{(1030 - 684) \times (1 - 0.844)}{1368 - 684} \right) + 0.844 = 0.922

Shapemaker report shielding factor values:

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