Wind Load Generation - IS 875 (Part 3): 2015 dialog

Used to automatically generate both wind load definition and wind load cases per the IS 875 (Part 3) : 2015 code.

Opens when the Wind Load Generator > IS 875 (Part 3) : 2015 tool is selected from the Load Generation group on the Loading ribbon tab.

Notes: The following limitations pertain to generation of IS 875 (Part 3) : 2015 wind loads:

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.

Wind Profile tab

The calculated wind intensity values (speeds and pressures) are tabulated and graphically plotted as the input parameters are updated. The calculated values are per Cl. 7.2 of IS 875 (Part 3) and the minimum pressure, pd ≥ 0.7×pz, is also considered.

Setting

Description

General Information

Setting	Description
Year of Publication	Select the edition of the IS-875 code from the drop-down list. 2015
Structure Type	Select the type of structure from the drop-down list: Rectangular Clad Building Unclad Building
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.

Wind Parameters

Setting	Description
Basic Wind Speed (Vb)	Either select the name of the location from the drop-down list to use the mapped wind speed per Annex A of IS 875 (Part 3) : 2015 or check the Custom to type the wind speed directly in m/s.
Risk Coefficient Factor (k1)	Select class of structure from drop-down option and corresponding k1 value will be automatically selected as per Table 1 of IS 875 (Part 3) : 2015. Alternatively, select Custom from the drop-down list to directly type the k1 value for use.
Topography Factor (k3)	Type the topographic factor to use. The value should be between 1 to 1.36 as per clause 6.3.3.1 of IS 875 (Part3) : 2015.
Importance Factor (k4)	Select the importance category of the structure from drop-down option and corresponding Importance Factor (k4) value will be selected as per Clause 6.3.4 of IS 875 (Part -3 ) : 2015. Alternatively, select Custom from the drop-down list to directly type the k4 value for use.
Terrain Category	Select terrain category from drop-down option and corresponding height factor (k2) will be automatically calculated as per Table 2 of IS 875 (Part 3) : 2015 and corresponding Aerodynamic Roughness Height (z0i) value will be automatically selected as per clause 6.3.2.1 of IS 875 (Part 3) : 2015. The Aerodynamic Roughness Height is used for calculating hourly mean wind speed factor (k2,i) and determined mean hourly wind speed at different height as per clause 6.4 of IS 875 (Part 3) : 2015. Alternatively, select Custom from the drop-down list to directly type the k2,i and z0i values for use.
Wind Directionality Factor (Kd)	Defaults to 1.0
Area Averaging Factor (Ka)	Defaults to 1.0
Combination Factor (Kc)	Defaults to 1.0

Wind Load Data tab - Rectangular Clad Building

Setting

Description

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.

Coefficients

Select the option for evaluating the coefficient factor. The associated table with the selection is made active.

Pressure Coefficient - select this option to specify parameters to calculate the pressure coefficients on building face per Cl. 7.3.2 and 7.3.3.
Force Coefficient - select this option to directly specify the Force Coefficient Factor (Cf) on the building per Cl. 7.4.2.

External Pressure Coefficient (Cpe)

Setting	Description
table	The calculated Cpe values for each direction and face are displayed in the table. Double-click to enter a custom value in any table cell. Custom values are highlighted. A Reset option is made active if any custom values are used in the table. Tip: A tool-tip will also display the calculated value for any cell.
Internal Pressure Coefficient (Cpi)	Check this option to include the Internal Pressure Coefficient (Cpi).
Building Permeability	Select the range of openings to overall building exterior from the drop-down list. This is used to select the Cpi and Cpnet values per Clause 7.3.2.1 of IS-875. Alternatively, select Custom from the drop-down list to type a value to use for Cpi
Use (-) Cpi	Check this option to use negative Internal Pressure Coefficient (Cpi) value to calculate Net Pressure Coefficient (Cpnet)

Force Coefficient (Cf)

Setting	Description
table	Type a Cf value to use for each face (default is 1.0).

Assignments

There are four method of assignments for the generated load cases:

Automatic - The program will select faces A, B, C, and D. The list of members in this selection are displayed in the read-only Member List cell.
Group - An existing group name is used to define the members which make up the building wind faces.
Member List - Each face is defined by typing a list of members.
Range - Type the minimum and maximum values for the global coordinates (in the units shown) for each face.

Check the Exclude option for an row to exclude assigning wind loads to this building face.

Wind Load Data - Unclad Frame Building

Setting

Description

Number of Frames

Select the number of frames in the structure along the wind direction.

Wind Direction

Select the wind direction for this load definition and load case.

Frame Information

Select the method for specifying the frame spacing:

Dimension - the actual distance between each frame in the units shown is entered in the Space Between Frames cell.
Ratio - the frame spacing ratio as indicated in Table 32 (Clause 7.4.3.4) of IS-875 is entered in the Spacing Ratio cell.

Setting	Description
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.
Width / Height	Type the overall dimensions of the frame. The default values are used based on the detected dimensions of the structure.

Force Coefficient

A separate table is listed for each frame in the structure. Select the frame number to display that table's values.

The intermediate values along with the calculated values are displayed in the table.

You must specify the Solidity Ratio (Φ) at each height interval of the structure in each frame table. For multiple frames, you must also specify the Effective Solidity Ratio (Φ_e) at each height interval for frames No. 2 and higher.

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 for frames No. 2 and higher.

Assignments

There are three method of assignments for the generated load cases:

Group - An existing group name is used to define the members which make up the frames.
Member List - Each frame is defined by typing a list of members.
Range - Type the minimum and maximum values for the global coordinates (in the units shown) for each frame.

Check the Exclude option for an row to exclude assigning wind loads to this frame.