В этой статье, 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, и 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

мы обсудим влияние топографии на ветровую нагрузку на конструкции путем расчета топографического фактора 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. В этой статье, 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°.

фигура 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 7-16:

Стол 1. Surface Roughness definition based on Section 26.7.2 ASCE 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 7-16 следующее:

Стол 2. Exposure Category definition based on Section 26.7.3 ASCE 7-16.

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

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

фигура 3. Upwind Surface Roughness condition required For Exposure D – кейс 1.

фигура 4. Upwind Surface Roughness condition required For Exposure D – кейс 2.

The Exposure Category shall be determined for each wind source direction. Using an example site location – “1200 S DuSable Lake Shore Dr, Чикаго, НАШИ 60605, Соединенные Штаты Америки”, lets analyze this for each direction.

фигура 4. Sample location for Exposure Category analysis.

Assuming the mean roof height of the structure is 25 фут ( \( 20h = 500 фут \)), 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 \( d_{1} \) является 5000 фут (1524 м), we need to check for Exposure D, where Surface Roughness D is dominant for the whole 5000 ft stretch:

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

С рисунка 5, we can already conclude that wind source directions N, РОДИЛСЯ, и E have Surface Roughness D for the whole 5000 ft stretch. Следовательно, these wind source directions are Экспозиция D.

Condition 2. Determine if Exposure D using Figure 2

Using Figure 4 – where the distance \( d_{1} \) является 5000 фут (1524 м) and distance \( d_{2} \) равно 600 фут (183 м), we need to check for Exposure D. С рисунка 5, this can only be applied for wind source direction from SE:

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

For wind source direction SE, с использованием \( d_{2} знак равно 600 фут \), we can consider that this section is Surface Roughness B. тем не мение, for distance \( d_{1} знак равно 5000 фут \), the section is not 100% Surface Roughness D. следовательно, SE should not be considered as Exposure D.

Condition 3. Determine if Exposure B using Figure 1

Using Figure 3 – where the distance \( d_{1} \) является 1500 фут (457 м) поскольку \( час < 30 фут \), we need to check for Exposure B.

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

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

Condition 4. If conditions 1 в 3 are not true, следовательно, the terrain is Exposure C.

Следовательно, for wind source direction SE, it is classified as Exposure Category C. В итоге, the exposure categories for each wind source direction is shown in Figure 8 ниже.

фигура 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 \( Ниже приведены различные способы определения коэффициентов давления грунта для расчета удельного сопротивления трения свай в песке.{с участием} \), Топографический фактор \( Ниже приведены различные способы определения коэффициентов давления грунта для расчета удельного сопротивления трения свай в песке.{T} \), and Gust-effect Factor \( грамм \) 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°.

 

фигура 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) НБЦК 2015:

Стол 3. Definition of terrain categories as defined in Section 4.1.7.3(5) НБЦК 2015.

Visualizing the options in Table 3:

фигура 10. Definition of Rough Terrain as defined in Section 4.1.7.3(5) НБЦК 2015.

фигура 10. Definition of Open Terrain as defined in Section 4.1.7.3(5) НБЦК 2015.

Based on Section 4.1.7.3(5) НБЦК 2015, it is permitted to interpolate the Фактор воздействия \( C_{е} \) in intermediate terrain. If the rough terrain distance from the structure location is greater than or equal to 1km or 20 раз больше высоты конструкции, смотря что больше, местность можно рассматривать как пересеченная местность, и если расстояние меньше 50 м, это считается Открытая местность. В противном случае, the Exposure Factor \( C_{е} \) согласно разделу 4.1.7.3(5) will be calculated from the boundary values. This can be visualized in Figure 11 ниже.

фигура 11. Definition of Intermediate Terrain as defined in Section 4.1.7.3(5) НБЦК 2015.

To further illustrate this, let’s use an example site location – “657 Masters Rd SE, Калгари, AB T3M 2B6, Канада,” assuming the structure height \( ЧАС \) является 25 м ( \( 20H = 500 м \)).

фигура 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 \( 20 ЧАС \) radius from the site location.

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

С рисунка 13, we can say that the wind source directions РОДИЛСЯ, Е, и ЮВ are classified as Open terrain as the rough terrain length for each direction is less than 50m from the site location. более того, 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 км. 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.

фигура 14. Approximate rough terrain length measured from site location for SW wind source direction equal to 574 м.

фигура 15. Approximate rough terrain length measured from site location for S wind source direction equal to 249 м.

From the analysis above, definitely the wind source directions with Open Terrain will definitely yield the conservative values. тем не мение, 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)

Для AS / NZS 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 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 1170.2 (2021):

Стол 4. Definition of terrain categories as defined in Section 4.2.1 AS / NZS 1170.2 (2021).

In determining the terrain category for a direction, a lag distance equal to \( 20 с участием \) from the structure location shall be neglected. С этого момента, an offset distance (averaging distance) из 500 м или \( 40 с участием), whichever is larger, shall be used as shown in Figure 16 ниже. В \( с участием \) value is equal to the average roof height, \( час \), when it is less than or equal to 25 м. 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 \( M_{с участием,кошка} \) ценности, depending on the length of each terrain category, как показано на рисунке 4.1 AS / NZS 1170.2 (2021). В этой статье, we shall only consider a homogeneous terrain category within the averaging distance.

фигура 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″Е – assuming the mean roof height \( час \) является 10 м ( где \( 20z = 20h = 200 м \) и \( 40г = 400 м \)).

фигура 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 \( 40с участием \) расстояние, we can already classify each wind source direction. Assuming the buildings on N, NE and E, are buildings that are 5 в 10 м высотой, we can classify these to Terrain Category 3 (TC3) как показано в таблице 4. For wind source directions SE, S, ЮЗ, and W, since these are grass plains without obstructions, we can classify these as Terrain Category 1 (TC1). в заключение, for wind source direction NW, we can deduce that there are more than two but less than 10 buildings per hectare, with scattered houses. Следовательно, we can classify this as Terrain Category 2.5 (TC2.5).

фигура 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 – Измерить расстояние и Расстояние Радиусы инструменты.

фигура 19. Инструменты измерения расстояния представлены в генераторе нагрузки SkyCiv.

В Измерить расстояние инструмент используется для создания круга из выбранной точки на карте и отображения его радиуса в метрах.. Сюда, вы можете измерить расстояния от анализируемого местоположения в определенных местах. This can be used in measuring in NBCC 2015 для Протяженность пересеченной местности с наветренной стороны used in calculating Фактор воздействия \( C_{е} \). Clicking the circle generated will clear it from the map.

фигура 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.

С другой стороны, в Расстояние Радиусы введено, чтобы пользователи могли рисовать круги с указанными расстояниями от местоположения для каждой категории источников ветра.. 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.

фигура 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.

фигура 22. Возможность в настройках редактировать расстояния для инструмента «Радиусы расстояний» в генераторе нагрузки SkyCiv..

Take note that users must edit the distance values as these are not automatically calculated by the software. Using this for ASCE 7 и 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 \( M_{с участием,кошка} \) ценности. Вместо, 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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Ссылки:

• Минимальные проектные нагрузки для зданий и других сооружений. (2017). ASCE / SEI 7-16. Американское общество гражданских инженеров.
• Национальный исследовательский совет Канады. (2015). Национальный строительный кодекс Канады, 2015. Национальный исследовательский совет Канады.
• Standards Australia (2021), Structural Design Actions. Часть 2 Действия ветра, Australian/New Zealand Standard AS/NZS1170.2:2021, Standards Australia, Сидней, NSW, Австралия.
• = Расстояние с подветренной стороны от гребня до места, где перепад высот составляет половину высоты холма или откоса.