To add a wind load definition and load cases for the Indian IS-875 (Part 3):
2015 code, use the following procedure.
This procedure is used to generate a series of wind intensity vs. height
values based on the procedure of the IS-875 (Part 3): 2015 code. The wind intensity
will either be the net pressure coefficient or the force coefficient multiplied by
the design wind pressure, based on the user selection.
Note: This procedure may be used for Rectangular Clad Buildings and Unclad Frame
Buildings. The Load & Definition dialog can be used to also create definitions
for Signs or Lattice Tower structures.
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.
- 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.
-
On the Loading ribbon tab, select in the Load Generation group.
The Wind Load Generation - IS 875 (Part 3) : 2015
dialog opens.
-
Specify the General Information for the wind load:
-
Select the Type of Structure from the drop-down
list.
- Rectangular Clad Building
- Unclad Frame Building
The parameters on the
Wind Load Data tab
update based on this selection.
-
Type the Structure Height and Ground
Level Elevation values.
The default values are taken as the maximum Y coordinate of the
structure and zero, respectively.
-
Type the Height Interval for Intensity to use
for developing the height vs. intensity values for the wind load
definition.
The default value is 5 m.
-
Check the Custom option for the
Starting Loadcase No and then type a load
case number for the first generated wind load case.
The default is the next load cases number after the highest load cased
in the model.
-
Specify the Wind Parameters for the wind load:
-
Specify the Basic Wind Speed (Vb) by
either:
- selecting a city from the drop-down list
- checking the Custom option and typing the
basic wind speed in m/s
-
Specify the Risk Factor Coefficient (k1) by
either:
- selecting the class of structure the drop-down list
- selecting Custom from the drop-down list
and typing the value for k1
-
Type the Topography Factor (k3) to use.
-
Specify the Importance Factor (k4) by
either:
- selecting the importance category from the drop-down
list
- selecting Custom from the drop-down list
and typing the value for k4
-
Specify the Aerodynamic Roughness Height (z0i)
by either:
- selecting the Terrain Category from the
drop-down list
- selecting Custom from the drop-down list
and typing the value for z0i. The values of the Height Factor (k2)
may also be entered for each height interval in the wind intensity
data table for the custom option.
-
Type the Wind Directionality Factor (Kd).
-
Type the Area Averaging Factor (Ka).
-
Type the Combination Facotr (Kc).
The wind intensity table and graph update with the resulting
values.
-
Select the Wind Load Data tab.
-
Enter the wind load data based on the selected structure type
Rectangular Clad Buildings
Setting |
Description |
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:
-
None - no coefficient factor
is multiplied with wind intensity value.
-
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.
|
Pressure Coefficient on Face |
Use these options when the Use Coefficient
Factor option selected is Pressure
Coefficient:
Setting |
Description |
Wind on Face |
Select the face of the structure (as labeled in
the diagram in the dialog) to which this wind definition is
applicable. |
External Pressure Coefficient (Cpe) |
Select to use either the Code
Calculated or Custom
(manually typed) value of Cpe. If the maximum range of
l/w from Tabe 5 of IS 875 (Part 3):
2015 is exceeded, then the upper values of Cpe for
3/2 < l/w < 4 are still used. You
may also enter custom Cpe values. |
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 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 |
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.
|
-
Select the method of assigning the wind loads to the model:
Type of Structure | Assignment method options |
---|
Rectangular Clad Building |
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.
|
Unclad Frame Building |
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.
|
-
Click Generate.
For a rectangular clad building
type, a series of four load definitions and eight load cases are generated, each with
four load items for each of the four wind directions. The definitions contain the load
vs design wind pressure values. For an unclad frame type, the definitions include
height vs intensity. For this case, the intensity generated is the force coefficient
(Cf or Cf') multiplied by the design wind pressure (Pd).
The wind load generation data is
stored within the STAAD input file.You may edit the height vs design
wind pressure values generated by clicking Edit in the
Load & Definition dialog when one of the
wind definition intensities is selected. After editing and regenerating the wind
loads, all previous wind definitions and associated loads are deleted.