Technical Reference 2007

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.

General Format

DEFINE WIND LOAD

TYPE j

INTENSITY p1 p2 p3 … pn HEIGHT h1 h2 h3 … hn

EXPOSURE e1 { JOINT joint-list | YRANGE f1 f2 | ZRANGE f1 f2 }

Repeat EXPOSURE command up to 98 times.

Where:

j = wind load system type number (integer)

p1,p

2,p

3… p

n = wind intensities (pressures) in force/area. Up to 100

different intensities can be defined in the input file per type.

h1,h

2,h

3… h

n = 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, e

2 … e

m = 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 f

2 = 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.

Description

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

of 45.31.3 Definition of Wind Load

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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 h

1. The second intensity ( p

2) will be applied to any part of the structure that has

vertical coordinates between the first two heights (h1 and h

2) 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) X (Influence Area) X (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) X (influence width for joint)

Notes

a. All intensities, heights and ranges must be provided in the current unit system.

b. If necessary, the INTENSITY, 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

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.

Persistency of Parameters used to Generate ASCE Wind Loads

This feature is effective STAAD.Pro 2006

In the graphical environment, under the General-Load-Definitions-Wind Definitions page, there is a facility 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, therefure, 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



Technical Reference 2007

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