IS-875 (Part 3): Wind Load dialog
Used to enter code parameters for generating wind intensity values based on the IS-875 (Part 3): Wind Load code
- The wind profile for the loading is calculated based on Y ordinate set to 0 rather than lowest point of the building. Thus, the topographical factor (k3) may not be relevant and should be applied with caution.
- Only Y-up models may be used (that is, the
SET Z UP
command may not be used). - The resulting wind load intensity vs. height values generated for IS 875 (Part 3) : 2015 are in metric, regardless of the current input units.
- The dynamic effect of wind load is not considered.
- Cl. 6.3.2.4 and Annex B for changes in terrain categories (Table 3 Fetch and Developed Height Relationships) are not considered.
- For rectangular buildings, the frictional drag per Cl. 7.4.1 is not considered.
- For free standing walls and hoarding type structures, the check for oblique wind loads per Cl. 7.4.2.3 is not considered.
- For lattice tower structures, the corner wind effect on square lattice towers with flat-sided members per Cl. 7.4.3.5(b) is not considered.
- For unclad frame builds, this feature can be used to generate the wind load in one direction only (for example, +X, -X, +Z, or -Z). To generate wind load in multiple directions, the manual workflow must be used.
Common tab
Setting | Description | ||||||||||
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Year of Publication | Select the edition of the IS-875 code from the drop-down
list.
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Structure Type | Select the type of structure from the drop-down list:
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Maximum Height | By default, this dimension is taken as the maximum Y coordinate of the structure. You may also type a Height value. | ||||||||||
Ground Level Elevation | (Read-only) Always assumed as zero. | ||||||||||
Height Interval for Intensity | The vertical interval (along the global Y axis) for calculating the wind intensity. | ||||||||||
Basic Wind Speed (Vb) |
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Wind Parameters | Based on the selected or typed values, the Design Wind Speed is
automatically calculated using the formula ( Vb × k1 × k2 × k3 ×
k4 ) per clause 6.3 of IS 875 (Part 3) : 2015 at given height
interval. A Height vs. Velocity graph is plotted for the value of height and
design wind speed (Vz).
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<structure type> tab
Rectangular Clad Buildings
Setting | Description | ||||||||||||
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Wind Direction | Select one of the global directions for the wind: +X, -X, +Z, or -Z. | ||||||||||||
Building Dimensions | By default, the dimensions are calculated based on the minimum and maximum global coordinates of the structure along the X, Z, and Y global axes, respectively. You may also type the Length Along X (Lx), Length Along Z (Lz), and Height (H) dimension values. | ||||||||||||
Use Coefficient Factor | Select the option for evaluating the coefficient factor:
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Pressure Coefficient on Face | Use these options when the Use Coefficient
Factor option selected is Pressure
Coefficient:
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Force Coefficient on Building | Type the Force Coefficient (Cf) value as per clause 7.4.2 of IS-875 when the Use Coefficient Factor option selected is Force Coefficient. |
Unclad Frame Building
Setting | Description |
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Frame Type | Select if the structure contains a
Single frame or
Multiple frames spaced along the wind
direction. For either frame type, you must specify the
Solidity Ratio (Φ) at each height interval of the structure in the frame
information table. For multiple frames, you must also specify the
Effective Solidity Ratio (Φe
) at each height
interval. Providing the Solidity Ratio (Φ) for a single frame at the given height interval, the force coefficient (Cf) will be selected according to the user provided solidity ratio values from Table 31 of IS 875 (Part 3) : 2015 by interpolation. Providing the Effective Solidity Ratio (Φe ) for multiple frames at the given height interval, the shielding factor (H) will selected according to the user provided effective solidity ratio values from Table 32 of IS 875 (Part 3) : 2015 by interpolation. |
Member Profile Cross Section | Select if the cross section profile of the frame(s) is Flat Sided or Rounded. For rounded members, you must also specify the Diameter of the members used at each height interval in the frame information table. |
Frame Spacing Ratio | For Multiple frames, type the frame spacing ratio as indicated in Table 32 (Clause 7.4.3.4) of IS-875. |
Force Coefficient | The intermediate values along with the calculated values are
displayed in the table. If the Custom option is selected, then you must specify the Force Coefficient (Cf) values at each height interval. For multiple frames in the Custom option, you must also specify the Shielding Factor at each height interval in the table. |
Free Wall and Hoardings
Setting | Description | ||||||||||
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Walls or Hoarding Parameters |
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Height Above Ground | Select either the Automatic (calculated) or Custom option. For the automatic option, the height above ground (h') value used is taken as the structure height, H, minus the vertical dimension, h. The custom option lets you type a different value. | ||||||||||
Force Coefficient |
The Force coefficients factor (Cf) will be calculated automatically based on the width to height ratio (horizontal dimension, b, divided by vertical dimension, h) and whether the free-standing wall or hoarding are above ground or on ground as given in Table 26 of IS 875 Part (3) : 2015. No interpolation of Table 26 is assumed. So if a width to heigh ratio, b/h, is between to tabulated values, then the next greater value of Cf is used. If the Custom option is selected, then you must specify the Force Coefficient (Cf) value. |
Lattice Tower
Setting | Description | |||||||||||||
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Tower Information |
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Solidity Ratio | For either tower type, you must specify the Solidity Ratio of the front face (Φ) at each height interval of the structure in the solidity ratio table. | |||||||||||||
Force Coefficient |
The Force coefficients factor (Cf) will be calculated at each height interval automatically based solidity ratio and the tower type as per the following table (with linear interpolation between tabulated values). The force coefficient table also displays the intermediate calculated values.
If the Custom option is selected, then you must specify the Force Coefficient (Cf) value. |
Design Wind Pressure tab
This tab displays the resulting height vs. design wind pressure (pd) chart and graph per Cl. 7.2 of IS 875 (Part 3). The program includes a check for the minimum design wind pressure of 0.7×pz. The intensity values generated are the net pressure coefficient or the force coefficient times the design wind pressure (pd).
Setting | Description |
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Wind Directionality Factor (Kd) | Defaults to 1.0. |
Area Averaging Factor (Ka) | Defaults to 1.0. |
Combination Factor (Kc) | Defaults to 1.0. |