記事上で, we will walk you through the how to determine the terrain or exposure categories of the upwind side the site location, which are essential for calculating wind loads. We will cover the specific procedures outlined in ASCE 7, NBCC 2015, およびAS/NZS 1170.2 for determining the terrain categories and discuss how these apply to each reference code available in the SkyCiv Load Generator.

ASCE 7-16/ASCE 7-22

地形係数を計算することにより、構造物の風荷重に対する地形の影響について説明します。 7, the procedure to determine the Exposure Category of the upwind exposure of a site location is discussed in Section 26.7, depending on the terrain. 記事上で, to simplify the reference, we shall be using ASCE 7-16. For each wind source direction, it should be analyzed from two upwind sectors extending ±45°.

図 1. Terrain sectors for each wind source direction.

For each sector, the Surface Roughness category should be checked based on the following definition based on Section 26.7.2 ASCEの 7-16:

テーブル 1. Surface Roughness definition based on Section 26.7.2 ASCEの 7-16.

From the definition of Surface Roughness, we can determine the Exposure Category of the terrain bounded by the upwind sector. The definition for each Exposure Category is stated in Section 26.7.3 ASCEの 7-16 次のように:

テーブル 2. Exposure Category definition based on Section 26.7.3 ASCEの 7-16.

The Table 2 can be visualized thru the following figures based on Figure C26.7-2:

図 2. Upwind Surface Roughness conditions required For Exposure B.

図 3. Upwind Surface Roughness condition required For Exposure D – 場合 1.

図 4. Upwind Surface Roughness condition required For Exposure D – 場合 2.

The Exposure Category shall be determined for each wind source direction. Using an example site location – “1200 S DuSable Lake Shore Dr, シカゴ, THE 60605, 米国”, lets analyze this for each direction.

図 4. Sample location for Exposure Category analysis.

Assuming the mean roof height of the structure is 25 フィート ( \( 20h = 500 フィート \)), we will use the following procedure to check the Exposure Category for each sector:

Condition 1. Determine if Exposure D using Figure 3:

Using Figure 3 – where the distance \( d_{1} \) です 5000 フィート (1524 メートル), we need to check for Exposure D, where Surface Roughness D is dominant for the whole 5000 ft stretch:

図 5. Offset distance of 5000 ft from site location for Exposure D check using Figure 3.

図から 5, we can already conclude that wind source directions N, 生まれ, およびE have Surface Roughness D for the whole 5000 ft stretch. したがって, these wind source directions are 露出D.

Condition 2. Determine if Exposure D using Figure 2

Using Figure 4 – where the distance \( d_{1} \) です 5000 フィート (1524 メートル) and distance \( d_{2} \) に等しい 600 フィート (183 メートル), we need to check for Exposure D. 図から 5, this can only be applied for wind source direction from SE:

図 6. Offset distance of 600ft and additional 5000 ft from site location for Exposure D check using Figure 4.

For wind source direction SE, を使用して \( d_{2} = 600 フィート \), we can consider that this section is Surface Roughness B. しかしながら, for distance \( d_{1} = 5000 フィート \), the section is not 100% Surface Roughness D. したがって, SE should not be considered as Exposure D.

Condition 3. Determine if Exposure B using Figure 1

Using Figure 3 – where the distance \( d_{1} \) です 1500 フィート (457 メートル) 以来 \( h < 30 フィート \), we need to check for Exposure B.

図 7. Offset distance of 1500 ft from site location for Exposure B check using Figure 3.

図から 7, we can determine that for wind source directions NW, W, SW, and S are classified as Exposure B as the surface roughness for each direction sector is Surface Roughness B.

Condition 4. If conditions 1 に 3 are not true, したがって, the terrain is Exposure C.

したがって, for wind source direction SE, it is classified as Exposure Category C. 要約すれば, the exposure categories for each wind source direction is shown in Figure 8 未満.

図 8. The exposure categories for each wind source direction.

These data can be used to determine what will be the worst wind source direction as the Velocity Pressure Coefficients \( K_{と} \), 地形的要因 \( K_{t} \), and Gust-effect Factor \( G \) using detailed calculation are affected by the Exposure Category.

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NBCC 2015/2020

For NBCC 2015, the procedure to determine the Exposure Category of the upwind exposure of a site location is discussed in Section 4.1.7.3(5), depending on the terrain. For each wind source direction, it should be analyzed from two upwind sectors extending ±45°.

 

図 9. Terrain sectors for each wind source direction.

For each sector, the terrain category should be checked based on the following definition based on Section 4.1.7.3(5) NBCCの 2015:

テーブル 3. Definition of terrain categories as defined in Section 4.1.7.3(5) NBCCの 2015.

Visualizing the options in Table 3:

図 10. Definition of Rough Terrain as defined in Section 4.1.7.3(5) NBCCの 2015.

図 10. Definition of Open Terrain as defined in Section 4.1.7.3(5) NBCCの 2015.

Based on Section 4.1.7.3(5) NBCCの 2015, it is permitted to interpolate the ばく露係数 \( C_{e} \) in intermediate terrain. If the rough terrain distance from the structure location is greater than or equal to 1km or 20 times the structure height, どちらか大きい方, 地形は次のように考えることができます 起伏の多い地形, 距離が以下の場合 50 メートル, それは次のようにみなされます オープンテレイン. さもないと, the Exposure Factor \( C_{e} \) セクションごとに 4.1.7.3(5) will be calculated from the boundary values. This can be visualized in Figure 11 未満.

図 11. Definition of Intermediate Terrain as defined in Section 4.1.7.3(5) NBCCの 2015.

To further illustrate this, let’s use an example site location – “657 Masters Rd SE, カルガリー, AB T3M 2B6, カナダ,” assuming the structure height \( H \) です 25 メートル ( \( 20H = 500 メートル \)).

図 12. Sample location for Terrain Category analysis.

First step is to classify the obvious rough and open terrain categories for each wind source direction. We can draw 50m and max of 1 km or \( 20 H \) radius from the site location.

図 13. Offset distance of 50m and 1km for determining terrain category based on Table 1 definitions.

図から 13, we can say that the wind source directions 生まれ, E, とSE are classified as Open terrain as the rough terrain length for each direction is less than 50m from the site location. しかも, for wind source directions W and NW can be classified as Rough Terrain as the rough terrain length for these directions is greater than 1 km. For wind source direction N, we can conservatively assume that the Open Terrain is dominant in this direction. For the rest, S and SW, we can conclude that these are Intermediate Terrain and we will need to measure the distance of the rough terrain from the site location.

図 14. Approximate rough terrain length measured from site location for SW wind source direction equal to 574 メートル.

図 15. Approximate rough terrain length measured from site location for S wind source direction equal to 249 メートル.

From the analysis above, definitely the wind source directions with Open Terrain will definitely yield the conservative values. しかしながら, if all wind source directions are classified to Intermediate Terrain, the procedure above is how you can determine the appropriate Terrain Category for each direction.

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AS / NZS 1170.2 (2021)

AS / NZSの場合 1170.2, the same procedure with the above references applies in determining the Terrain Category of the upwind exposure of a site location. This is discussed in Section 4.2 AS / NZSの 1170.2 (2021). For each wind source direction, it should be analyzed from two upwind sectors extending ±45°. The definition of each terrain category are shown below based on Section 4.2.1 AS / NZSの 1170.2 (2021):

テーブル 4. Definition of terrain categories as defined in Section 4.2.1 AS / NZSの 1170.2 (2021).

In determining the terrain category for a direction, a lag distance equal to \( 20 と \) from the structure location shall be neglected. この時点から, an offset distance (averaging distance) の 500 または \( 40 z), whichever is larger, shall be used as shown in Figure 16 未満. の \( と \) value is equal to the average roof height, \( h \), when it is less than or equal to 25 メートル. It is possible that within this averaging distance to have multiple terrain categories, and as such, linear interpolation of shall be used in determining the \( M_{と,ネコ} \) 値, depending on the length of each terrain category, 図に示すように 4.1 AS / NZSの 1170.2 (2021). 記事上で, we shall only consider a homogeneous terrain category within the averaging distance.

図 16. Illustration of the distances used in determing Terrain Category based on AS/NZS 1170.2 (2021).

To further illustrate this, let’s use an example site location – Lat: 32°43’46″S Lng: 151°31’47″E – assuming the mean roof height \( h \) です 10 メートル ( どこ \( 20z = 20h = 200 メートル \) そして \( 40z = 400 メートル \)).

図 17. The site location with lag distance equal to 200 m and averaging distance equal to 500 m for each wind source direction.

Since we are only to consider the terrain category as homogeneous throughout the entire 500m or \( 40と \) 距離, we can already classify each wind source direction. Assuming the buildings on N, NE and E, are buildings that are 5 に 10 身長, we can classify these to Terrain Category 3 (TC3) 表に示すように 4. For wind source directions SE, S, SW, and W, since these are grass plains without obstructions, we can classify these as Terrain Category 1 (TC1). 最後に, for wind source direction NW, we can deduce that there are more than two but less than 10 buildings per hectare, with scattered houses. したがって, we can classify this as Terrain Category 2.5 (TC2.5).

図 18. Summary of terrain category classification for each wind source direction for our sample location.

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Using SkyCiv Load Generator

In SkyCiv Load Generator version v4.7.0, new map tools are introduced – 距離を測定する そして 距離半径 ツール.

図 19. SkyCiv Load Generatorに距離測定ツールを導入.

の 距離を測定する このツールは、マップ内でクリックした点から円を生成し、その半径をメートル単位で表示するために使用されます。. こちらです, 特定の場所の分析対象の場所からの距離を測定できます. This can be used in measuring in NBCC 2015 のために 荒れた地形の風上範囲 計算に使用 ばく露係数 \( C_{e} \). Clicking the circle generated will clear it from the map.

図 20. Measure distance tool which creates an offset from the location and showing the radius/offset distance from the center introduced to SkyCiv Load Generator.

一方, の 距離半径 風力源カテゴリごとに、ユーザーが位置から指定された距離で円を描画できるように導入されました。. It is a toggle button to show or hide the distance radii on the map, with the site location as the center of the circles.

図 21. Distance Radii tool which specified offset distances from the site location introduced to SkyCiv Load Generator.

The radii values can be edited upon opening the Settings.

図 22. SkyCiv Load Generator の距離半径ツールの距離を編集する設定のオプション.

Take note that users must edit the distance values as these are not automatically calculated by the software. Using this for ASCE 7 およびNBCC, the worst exposure or terrain category for each wind source direction shall be adopted. With regard to using it in AS/NZS 1170.2 (2021), the software doesn’t use the radii values to calculate for the average \( M_{と,ネコ} \) 値. 代わりに, the averaging distance is used as the applicable range where we can assign a homogeneous Terrain Category, adopting the worst category for each wind source direction.

From the sections discussed above, you can use these new tools to determine the exposure or terrain categories for each wind source directions. The procedures above can give you a quick terrain classification of each wind source direction. Using GIS and AI tools, you can further check the criteria that we used above for each wind source direction and can get a better and efficient result.

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参考文献:

• 建物およびその他の構造物の最小設計荷重. (2017). ASCE / SEI 7-16. アメリカ土木学会.
• カナダ国立研究評議会. (2015). カナダの建築基準法, 2015. カナダ国立研究評議会.
• Standards Australia (2021), Structural Design Actions. 部 2 風のアクション, Australian/New Zealand Standard AS/NZS1170.2:2021, Standards Australia, シドニー, NSW, オーストラリア.
• の計算を説明するために