5.31.

3 Definition of Wind Load Page 1 of 4

5.31.3 Definition of Wind Load

This set of commands may be used to define some of the parameters for generation of wind loads on
the structure. See Section 5.32.12 for the definition of wind direction and the possible surfaces to be
loaded. Section 1.17.3 of this manual describes the two types of structures on which this load
generation can be performed.
The wind load generator can be used to generate lateral loads in the horizontal—X and Z (or Y if Z up)
—directions only.

The graphical user interface can be used to automatically generate the appropriate intensity
values via the ASCE-7: Wind Load dialog. See "Persistence of Parameters used to Generate
ASCE Wind Loads"

General Format
DEFINE WIND LOAD
TYPE j ( optional_comment )
{ intensity-definition | code-parameters }
EXPOSURE e1 { JOINT joint-list | YRANGE f1 f2 | ZRANGE f1 f2 }
Repeat EXPOSURE command up to 98 times.
Where:

intensity-definition or code-parameters data is entered based on either custom or

Russian code wind definitions. See "Wind Intensity Definition" or See "Russian Wind
Loads"
j = wind load system type number (integer)
optional_comment = A text string comment or description used to help identify the wind
load type.
p1,p2,p3… pn = wind intensities (pressures) in force/area. Up to 100 different intensities
can be defined in the input file per type.
h1,h2,h3… hn = corresponding heights in global vertical direction, measured in terms of
actual Y (or Z for Z UP ) coordinates up to which the corresponding intensities occur.
e1, e2 … em = exposure factors. A value of 1.0 means that the wind force may be
applied on the full influence area associated with the joint(s) if they are also exposed to
the wind load direction. Limit: 99 factors.
joint-list = Joint list associated with Exposure Factor (joint numbers or TO or BY) or enter
only a group name.
f1 and f2 = global coordinate values to specify Y (or Z if Z UP) vertical range for Exposure
Factor. Use YRANGE when Y is Up and ZRANGE when Z is Up (See the SET Z UP
command in Section 5.5).

If the command EXPOSURE is not specified or if a joint is not listed in an Exposure, the exposure
factor for those joints is chosen as 1.0.

mk:@MSITStore:C:\SProV8i%20SS6\STAAD\Help\Technical_Reference_2007.chm::/C... 23/11/2020
5.31.3 Definition of Wind Load Page 2 of 4

Wind Intensity Definition

For custom (including for ASCE 7) wind load definitions, the wind intensity at heights above ground
are defined as follows:
intensity-definition = INTENSITY p1 p2 p3 … pnHEIGHT h1 h2 h3 … hn

These values are automatically generated for ASCE 7 wind loads when the ASCE-7: Wind Load
dialog is used.

All intensities and heights are in current unit system. The heights specified are in terms of actual Y
coordinate ( or Z coordinates for Z UP ) and not measured relative to the base of the structure. The
first value of intensity (p1) will be applied to any part of the structure for which the Y coordinate ( or Z
coordinate for Z UP ) is equal to or less than h1. The second intensity ( p2) will be applied to any part
of the structure that has vertical coordinates between the first two heights (h1 and h2) and so on. Any
part of the structure that has vertical coordinates greater than hn will be loaded with intensity pn.
Only exposed surfaces bounded by members (not by plates or solids) will be used. The joint influence
areas are computed based on surface member selection data entered in section 5.32.12 and based on
the wind direction for a load case. Only joints actually exposed to the wind and connected to
members will be loaded. The individual bounded areas must be planar surfaces, to a close tolerance,
or they will not be loaded.
Exposure factor (e) is the fraction of the influence area associated with the joint(s) on which the load
may act if it is also exposed to the wind load. Total load on a particular joint is calculated as follows.
Joint load = (Exposure Factor) × (Influence Area) × (Wind Intensity)
The exposure factor may be specified by a joint-list or by giving a vertical range within which all joints
will have the same exposure. If an exposure factor is not entered or not specified for a joint, then it
defaults to 1.0 for those joints; in which case the entire influence area associated with the joint(s) will
be considered.
For load generation on a closed type structure defined as a PLANE FRAME, influence area for each
joint is calculated considering unit width perpendicular to the plane of the structure. You can
accommodate the actual width by incorporating it in the Exposure Factor as follows.
Exposure Factor (User Specified) = (Fraction of influence area) × (influence width for joint)

Notes
a. All intensities, heights and ranges must be provided in the current unit system.
b. If necessary, the INTENSITY and EXPOSURE command lines can be continued on to additional
lines by ending all but last line with a space and hyphen (-). Use up to 11 lines for a command.

Example
UNIT FEET
DEFINE WIND LOAD
TYPE 1
INTENSITY 0.1 0.15 HEIGHT 12 24
EXPOSURE 0.90 YRANGE 11 13
EXPOSURE 0.85 JOITN 17 20 22
LOAD 1 WIND LOAD IN X-DIRECTION
WIND LOAD X 1.2 TYPE 1

mk:@MSITStore:C:\SProV8i%20SS6\STAAD\Help\Technical_Reference_2007.chm::/C... 23/11/2020
5.31.3 Definition of Wind Load Page 3 of 4

For additional examples, see section 5.32.12 and example 15 in the Examples manual.
The Intensity line can be continued in up to 12 lines.
So the following
INT 0.008 0.009 0.009 0.009 0.01 0.01 0.01 0.011 0.011 0.012 0.012
0.012 HEIG 15 20 25 30 40 50 60 70 80 90 100 120
could be split as
INT 0.008 0.009 0.009 0.009 0.01 0.01 0.01 0.011 0.011 0.012 0.012
0.012 –
HEIG 15 20 25 30 40 50 60 70 80 90 100 120
or
INT 0.008 0.009 0.009 0.009 0.01 0.01-
0.01 0.011 0.011 0.012 0.012 0.012 HEIG 15 20 25 -
30 40 50 60 70 80 90 100 120
etc.

Russian Wind Loads

For wind loads per Russian codes SNiP 85 and SP 2011, the code parameters are defined as follows:
code-parameters = { SNIP 1985 | SNIP 2011 } PRESSURE f3 TERRAIN { A |
B | C } CLASSIFICATION { 1 | 2 | 3 }
Where:

SNIP 1985 — design according to previous design Code SNiP 2.01.07-85

SNIP 2011 — design according to renewed design Code SP 20.13330.2011
f3 = the characteristic value of wind pressure, always positive.
TERRAIN is terrain roughness category:

A. Coastal Zone.
B. Urban Zone.
C. Large City.
CLASSIFICATION:

1. Prismatic building structures,

2. General-type concrete structures,
3. General-type framed steel structures.

A structured modeled as a set of vertical members—such as is typically used to define a

cylindrical stack or chimney structure, and thus doe snot define a closed panel such as
defined by a frame formed from a number of columns and beams—is considered to be a
'Stick Structure'. See "General Format for Russian SP of SNiP Wind Loads" for additional
details.

mk:@MSITStore:C:\SProV8i%20SS6\STAAD\Help\Technical_Reference_2007.chm::/C... 23/11/2020
5.31.3 Definition of Wind Load Page 4 of 4

The loading has two components: static and dynamic. The dynamic effect is determined by
the number of modes included in the dynamic load case and changing the number of modes
considered using the CUT OFF MODE SHAPE command may result in a change in the
resulting wind force. See "Cut-Off Frequency, Mode Shapes, or Time" for details.

If the PRINT STATICS CHECK option is included in the analysis command, then the output
file will include a section on the SNiP wind load. This output will indicate both the static and
dynamic contributions to the wind load as well as the total applied at each node.

Persistence of Parameters used to Generate ASCE Wind Loads

This feature is effective STAAD.Pro 2006

In the graphical environment, in the Add New : Wind Definition dialog, you can click the Calculate as
per ASCE-7 button to generate the pressure versus height table per the ASCE 7 wind load
specifications per the 1995, 2002, or 2010 editions. The parameters which go into the derivation of
this table are not retained by the graphical environment but rather added into the STAAD input file so
they may be edited as needed. These values are not read by the STAAD engine directly and,
therefore, are not directly processed as a load but are rather used to generate the wind intensity
values which are used by the engine. An example of it is shown below.

Example
DEFINE WIND LOAD
TYPE 1
<! STAAD PRO GENERATED DATA DO NOT MODIFY !!!
ASCE-7-2002:PARAMS 85.000 MPH 0 1 0 0 0.000 FT 0.000 FT 0.000 FT 1 -
1 40.000 FT 30.000 FT 25.000 FT 2.000 0.010 0 -
0 0 0 0 0.761 1.000 0.870 0.850 0 -
0 0 0 0.866 0.800 0.550
!> END GENERATED DATA BLOCK
INT 0.0111667 0.0111667 0.0113576 0.0115336 0.0116972 0.0118503 0.0119944 -
0.0121307 0.0122601 0.0123834 0.0125012 0.0126141 0.0127226 0.012827 0.0129277 -
HEIG 0 15 16.9231 18.8461 20.7692 22.6923 24.6154 26.5385 28.4615 -
30.3846 32.3077 34.2308 36.1538 38.0769 40

Related Information
1.17.3 Wind Load Generator
Reference Materials
5.32.12.2 Generation of Loads
5.31.6 Reference Load Types - Definition
5.32.12 Generation of Loads
5.31 Definition of Load Systems

mk:@MSITStore:C:\SProV8i%20SS6\STAAD\Help\Technical_Reference_2007.chm::/C... 23/11/2020