STAAD Graphical Environment
Model Generation
2.3.7.12.1.3 Commands | Loading | Definitions | Wind Load
Purpose
The Wind Load menu option allows the user to define the parameters for automatic generation of wind loads on the structure.
This option can be accessed from the General | Load page also, as explained in Section 2.2.11
of this manual.
Description
STAAD.Pro is now capable of generating the wind pressure profile for a structure in
accordance with the ASCE-7-95 as well as the ASCE-7-02 codes. The pressure profile is the table of values of wind intensity versus height above ground.
The calculated pressure may then be applied on the structure to compute loads on members using the program’s built-in wind load generation algorithm for the closed as well as open-lattice type structures.
When the Wind Load menu option is selected, the New Wind Type dialog box appears, as shown below.
Figure 2. 578
Enter the “Type No.” which denotes a number by which the wind load type will be identified. Multiple wind types can be created in the same model. Click on the Add button within this dialog box and then click on Close.
Figure 2. 579
The newly created TYPE 1 wind definition will appear underneath Wind Definitions in the
Load dialog box as shown below.
Figure 2. 580
Select the TYPE 1 name in the tree control and click on the Add button. The dialog box shown below will prompt for the pressure profile (intensity) for this wind definition.
Figure 2. 581
As we said earlier, the pressure profile is the table of wind intensity versus height above ground. If we know that, that information can be typed into the box above. But, our goal is to calculate that. Hence, we click on the button Calculate as per ASCE-7.
The ASCE-7: Wind Load dialog box shown below will appear.
Figure 2. 582
The options shown in the dialog box are explained below:
Figure 2. 583 ASCE
-7-Depending on which version of the code to use, choose either 1995 or 2002.
Building classification category
Basic Wind Speed
Exposure Category
Structure Type
ASCE-7-95 ASCE-7-02 Building classification
category as obtained from Table 1-1 in ANSI/ASCE 7-95.
Building classification category as obtained from Table 1-1 in SEI/ASCE 7-02. Category can be I, II, III or IV.
ASCE-7-95 ASCE-7-02 Basic Wind Speed from
regional climatic data as described in Figure 6-1 in the ANSI/ASCE 7-95 code.
Basic Wind Speed as
described in section 6.5.4 of the SEI/ASCE 7-02 code.
ASCE-7-95 ASCE-7-02 Exposure category as per
clause 6.5.3 in the ANSI/ASCE 7-95 code.
Exposure category as described in section 6.5.6.3 of the SEI/ASCE 7-02 code.
ASCE-7-95 and ASCE-7-02
Select the type of structure that best fits the model from the available choices:
· Building structures
· Chimneys, Tanks and similar structures · Solid Signs
Consider Wind speed-up over hill or escarpment
Type of Hill or Escarpment
Height of Hill or Escarpment (H)
Distance upwind of crest (Lh)
· Latticed Framework · Trussed tower
The associated input pages will change depending on the selection of the type of structure.
ASCE-7-95 ASCE-7-02 If there are isolated hills and
escarpments that constitute abrupt changes in the general topography, the increase in speed can be considered as per clause 6.5.5 in the ANSI/ASCE 7-95 code. Select ‘Yes’ to consider wind speed-up over a hill or an escarpment and ‘No’ to ignore it.
If there are isolated hills and escarpments that constitute abrupt changes in the general topography, the increase in speed can be considered as per section 6.5.7 in the SEI/ASCE 7-02 code. Select ‘Yes’ to consider wind speed-up over a hill or an escarpment and ‘No’ to ignore it.
ASCE-7-95 ASCE-7-02 Select the type of hill, ridge
or escarpment on which the structure is located. The options available are 2-D Escarpment, 2-D Ridge and 3-D Axisymmetric Hill.
Select the type of hill, ridge or escarpment on which the structure is located, based on figure 6-4 of the SEI/ASCE 7-02 code. The options available are 2-D
Escarpment, 2-D Ridge and 3-D Axisymmetric Hill.
ASCE-7-95 ASCE-7-02 Specify the height of the hill
or escarpment relative to the upwind terrain (H in Figure 6-2 of the ANSI/ASCE-7-95 code).
Specify the height of the hill or escarpment relative to the upwind terrain (H in Figure 6-4 of the SEI /ASCE-7-02 code).
ASCE-7-95 ASCE-7-02 Specify the distance upwind
of crest to where the difference in general
elevation is half the height of the hill or escarpment (Lh in Figure 6-2 of the
Specify the distance upwind of crest to where the
difference in general
elevation is half the height of the hill or escarpment (Lh in Figure 6-4 of the
SEI/ASCE-Distance from the crest to the uilding (x)
ain Building Data
Figure 2. 58 Building Height
The height above ground to the highest point on the roof surface.
Building Length along the direction of Wind (L)
Length of building measured along the direction of wind.
Building Length ormal to the direction of Wind (B)
Length of building measured normal to the direction of wind.
Building atural Fre uency
Specify the natural frequency of the building to calculate Gust Effect Factor.
Building Damping atio
ANSI/ASCE-7-95 code). 7-02 code).
ASCE-7-95 ASCE-7-02 Specify the distance from the
crest to the building site. A negative value signifies the distance is in the downwind direction (X in Figure 6-2 of the ANSI/ASCE-7-95 code).
Specify the distance from the crest to the building site. A negative value signifies that the distance is in the
downwind direction (X in Figure 6-4 of the SEI/ASCE-7-02 code).
Specify the damping ratio to calculate Gust Effect Factor.
Enclosure Classification
t
d
ASCE-7-95 ASCE-7-02
Not applicable. Classify the building as open building, partially enclosed or enclosed as per the provisions of section 6.2 of SEI/ASCE-7-02.
ASCE-7-95 ASCE-7-02 Velocity Pressure exposure
coefficient calculated as per Table 6-3 of the
ANSI/ASCE-7-95 code.
Velocity pressure exposure coefficient that is calculated by STAAD.Pro as per Table 6-3 of the SEI/ASCE-7-02 code.
ASCE-7-95 ASCE-7-02 When wind speedup is
considered, Kzt is calculated as per Eq 6-2 of the
ANSI/ASCE-7-95 code. Users can modify the value by checking the Use box and keying in the required value in the edit box for Kzt.
When wind speedup is considered, Kzt is calculated as per Eq 6-4 of the
SEI/ASCE-7-02 code. Users can modify the value by checking the Use box and providing the required value in the edit box for Kzt.
ASCE-7-95 ASCE-7-02 Importance Factor I is
considered as per Table 6-2 of the ANSI/ASCE-7-95 code. Users can enter their own value by checking the Use box and keying in the required value in the edit box for I.
Importance Factor I is
considered as per section 6.2 of the SEI/ASCE-7-02 code. Users can enter their own value by checking the Use box and typing the required value in the edit box for I.
ASCE-7-95 ASCE-7-02
Not applicable. Wind directionality factor is calculated as per Table 6-4 of the SEI/ASCE-7-02 code. Users can modify the value by checking the Use box and typing the required value in
The list of parameters explained earlier corresponds to the structure type called uildin
Structures. When structure type is varied, some of those parameters change. Those parameters
that are different are explained below for each type of structure.
Structure type : Chimney Tan and similar Structures Height(H)
Height of the structure as defined by the term ‘h’ in Figure 6-19 of the SEI/ASCE 7-02 code.
Least Hori ontal Dimension (W)
Smaller of the plan dimensions. In case the cross section of the structure in plan is circular, the diameter needs to be specified.
Hori ontal Cross-Section Type
This is the cross section of the structure in plan as defined in Figure 6-19 of the SEI/ASCE 7-02 code. The available options include square with wind being normal to face or acting along the diagonal, hexagonal, octagonal and round.
Depth of protruding elements such as ri s and spoilers (D )
For round type cross sections, depth of protruding elements need to be defined which is a measure of the surface roughness as indicated in Figure 6-19 of the SEI/ASCE 7-02 code.
Cf
Force coefficient that is calculated by STAAD.Pro as per Figure 6-19 of the SEI/ASCE 7-02 code. The parameter is used for calculation of design pressure. If desired, users can enter their own value for Cf by checking the se box and typing the required value in the appropriate edit
box.
Structure type: Solid Signs Height (H)
Height of the structure which is used for calculating the height to width ratio as defined by the term ‘’ in Figure 6-20 of the SEI/ASCE 7-02 code.
Hori ontal Dimension of Sign ( )
Horizontal dimension of the solid sign
ertical Dimension of Sign ( )
Vertical dimension of the solid sign. If the sign is at the ground level, the height (H) and vertical dimension (N) should both be specified the same value.
Cf
Force coefficient that is calculated by STAAD.Pro as per Figure 6-20 of the SEI/ASCE 7-02 code. The parameter is used for calculation of design pressure. If desired, users can enter their own value for Cf by checking the se box and typing the required value in the appropriate edit
box.
Structure type: pen Signs Lattice Frame Wor
Ratio of Solid Area to Gross Area
Ratio of solid area to gross area as indicated by the term in Figure 6-21of the SEI/ASCE 7-02 code.
rientation of the mem ers exposed to wind
The type of member surfaces which are exposed to wind. Select flat-sided members or rounded members in Figure 6-21 of the SEI/ASCE 7-02 code.
Diameter of typical round member
Diameter for round members as defined by the term ‘D’ in Figure 6-21 of the SEI/ASCE 7-02 code.
Structure type : Trussed Tower Hori ontal Cross Section
The type of cross section of the tower in plan as defined in Figure 6-22 of the SEI/ASCE 7-02 code. The available options include square and triangle.
Figure 2. 585
Building Wall to generate Wind Load on:
Windward
Leeward
Side Wall
ASCE-7-95 ASCE-7-02 To generate the design wind
pressure for the windward side, choose this option. The pressure will be calculated as per Table 6-1 of the
ANSI/ASCE-7-95 code. The relevant equation is also displayed in the box just beneath the radio buttons.
To generate the design wind pressure for the windward side, choose this option. The pressure will be calculated as per Equation 6-23 of the SEI/ASCE-7-02 code. The relevant equation is also displayed in the box just beneath the radio buttons.
ASCE-7-95 ASCE-7-02 To generate the design wind
pressure for the leeward side, choose this option. As
before, the pressure will be calculated as per Table 6-1 of the ANSI/ASCE-7-95 code. The relevant equation will be displayed in the box just beneath the radio buttons.
To generate the design wind pressure for the leeward side, choose this option. The pressure will be calculated as per Equation 6-23 of the SEI/ASCE-7-02 code. The relevant equation will be displayed in the box just beneath the radio buttons.
ASCE-7-95 ASCE-7-02 To generate the design wind
pressure for the side wall, choose this option. As before, the pressure will be calculated as per Table 6-1 of the ANSI/ASCE-7-95 code. The relevant equation will be displayed in the box just beneath the radio buttons.
To generate the design wind pressure for the side wall, choose this option. As before, the pressure will be calculated as per Equation 6-23 of the SEI/ASCE-7-02 code. The relevant equation will be displayed in the box just beneath the radio buttons.
ASCE-7-95 ASCE-7-02 Gust effect factor as per
Table 6-1 of the
ANSI/ASCE-7-95 code. Users can modify the value by checking the se box and
Gust effect factor calculated as per section 6.5.8 of the SEI/ASCE-7-02 code. Users can modify the value by checking the se box and
Cp
Cpi
keying in the required value
in the edit box for G. typing the required value in the edit box for G. ASCE-7-95 ASCE-7-02
Wall pressure coefficient as per Fig 6-3 of the
ANSI/ASCE-7-95 code. Users can modify the value by checking the se box and
keying in the required value in the edit box for Cp.
External pressure coefficient. The product of external pressure coefficient & gust effect factor is considered as per Figures 11 through 6-17 of the SEI/ASCE-7-02 code. Users can modify the value of Cp by checking the
se box and typing the
required value in the edit box for Cp.
ASCE-7-95
Internal pressure Coefficients as per Table 6-4 of the ANSI/ASCE-7-95 code. Users can modify the value by checking the se box
and keying in the required value in the edit box for GCpi.
The table on the right displays the intensities at various heights. Click on to arrive at the dialog box shown below.
Figure 2. 58
The intensity vs. height calculation as per the ANSI/ASCE-7-95 code is available as shown in the previous figure. Click on Add to add the load definition. Exposure factors need to be defined by the user as before.
The defined wind loading can then be applied to the structure following the usual method. For details on generation of wind load, refer to section 5.32.12: Generation of Loads from the
STAAD Technical Reference Manual.
ote
Using this feature, one can define different intensity vs. height data for the windward side, leeward side and side walls for a structure. Each can be defined as a different load type and then applied in the relevant direction with appropriate direction factor.
Cpi
ASCE-7-02
Internal pressure Coefficients as per Figure 6-5 of the SEI/ASCE-7-02 code. Users can modify the value by checking the se box
and typing the required value in the edit box for GCpi.
The table on the right displays the intensities at various heights. Click on to arrive at the dialog box shown in the next figure.
Figure 2. 587
The previous figure shows the result of the work. The final result of those operations is the intensity vs. height calculation as per the SEI/ASCE-7-02 code.
Click on Add to add the load definition.
The defined wind loading can then be applied to the structure following the same procedure as in prior versions of the program. For details on the command syntax for generation of wind loads, refer to section Generation o Loads from the STAAD Technical Reference Manual and example problem 15 in the Examples manual.
ote
The option we encountered earlier regarding the windward side, leeward side and side walls tells us that the pressure profile for each of those has to be individually determined under a unique type number. Thus, generating the profile for the 3 sides of the building constitutes 3 separate steps and thus, 3 separate types. Each type can then be applied with one load case or separate load cases and then applied in the relevant direction with the
Exposures
The E posure tab is used to modify the influence area of the wind load associated with particular joints in the structure. By default, the exposure factor is 1.0, thus the wind force is applied on the full influence area associated with the joint(s). Click on Add to add this load under the current load case in the Load dialog box.
Figure 2. 588
After defining a Wind Load, see Section 2.3.7.12.6for information on applying the load to the structure.
