Wind Loads

In MIDAS/Gen, the automatic data entry of wind loads according to various standards is applicable for common buildings where each story can be defined and can reasonably act as a rigid diaphragm. The following procedure is observed :

The structure must be modeled so that the gravity acts in the direction opposite to the GCS Z-direction.

When the ground level is entered, the parts below this level are considered as underground stories and neglected in the wind load calculation. If the ground level is not specified, the lowest part of the modeled structure is assumed to be the ground level by default.

It is recommended that be used to auto-generate the data necessary for the stories and the application of wind loading. Where openings exist at a particular story, adjust the width of the wind pressure area.

Once the floor diaphragm is defined in Story, the X-, Y-displacement degrees-of-freedom and the rotational degree-of-freedom about the Z-axis between all the nodes on the plane (plane parallel to the GCS X-Y plane) are constrained.

In addition, a part or all of the constrained nodes can be separated from the rigid floor diaphragm using Floor Diaphragm Disconnect.

IBC 2000 (ASCE7-98): International Building Code 2000

UBC (1997): UBC 97 standards

ANSI (1982): ANSI standards

NBC (1995): National Building Code of Canada

Eurocode-1 (1992): Basis of Design and Actions on Structures

BS6399 (1997): British Standard 6399 Loading for buildings

 IS875(1987): Indian Standard

Taiwan (2002): Taiwan Building Code

 

(available upon request)

Japan (Arch, 2004): Loading Specifications and Commentaries for Buildings

Japan (Arch, 2000): Loading Specifications and Commentaries for Buildings

Japan (1987): Loading Specifications and Commentaries for Buildings

Korean (Arch, 2000): Buildings loading criteria and commentaries

Korean (Arch, 1992): Regulations related to structural criteria for buildings

China (GS50011-2001): Code for Seismic Design of Building

 

Once the data required for the calculation of wind loads are defined, auto-calculate wind loads for each story in connection with the story data generated in Story. Use to verify the auto-calculated wind loads.

Wind load generation

 

1) Wind load calculation

If a floor area changes at a particular story level, the area subject to wind pressure is based on the sum of (A1=B1*h1/2) and (A2=B2*h2/2) relative to the corresponding story level.

 

Fig. 2 Elevation   

 

Fig. 3 Plan  

 

2) External Pressure Coefficient

Based on L/B2 for the upper portion and L/B1 for the lower portion

3) Design Pressure

Actual distribution of the wind pressure is parabolic, but MIDAS/Gen expresses it in a stepped distribution because the design pressure is taken at the story levels as per Fig. 2.

 

From the Main Menu select Load > Wind Loads.

Select Static Loads > Wind Loads in the Menu tab of the Tree Menu.

Access Wind Loads to activate the dialog box defining the wind loads. Click to display the dialog box shown below.

 

Add/Modify Wind Load Code dialog box

 

Load Case Name

Select the load case name to be associated with the wind load. Click to the right to enter or modify new load cases.

 

Wind Load Code

Select the standards to be applied to the wind load calculation.

IBC 2000(ASCE7-98): International Building Code 2000

UBC (1997): UBC 97 standards

ANSI (1982): ANSI standards

NBC (1995): National Building Code of Canada

Eurocode-1 (1992): Basis of Design and Actions on Structures

BS6399 (1997): British Standard 6399 Loading for buildings

IS875 (1987): Indian Standard

Taiwan (2002):  Taiwan Building Code

 

Description

Enter a short description.

 

Wind Load Parameters

Enter the parameters to be applied to the wind load calculation.

IBC 2000(ASCE7-98)

Simplied Procedure

Basic Wind Speed

Importance Factor

Exposure Category

Analytical Procedure

Basic Wind Speed

Wind Directionality Factor

Important Factor

Exposure Category

Mean Roof Height

Gust Effect Factor

Gust Factor Parameter

X-Breadth (Bx)

Y-Breadth (By)

X-Natural Frequency

Y-Natural Frequency

Damping Ratio

: Calculate Gust Factors

Gust Factor X

Gust Factor Y

Load Evaluation Using Force Coefficient : Determine whether to calculate load using wind force coefficient.

 

UBC (1997)

Projected Area Method

Exposure Category

Basic Wind Speed

Importance Factor

Pressure Coefficient

Normal Force Method

Exposure Category

Basic Wind Speed

Importance Factor

Mean Roof Height

 

ANSI (1982)

Exposure Category

Basic Wind Speed

Importance Factor

Windward Coefficient: Windward wind pressure coefficient

Leeward Coefficient: Leeward wind pressure coefficient

 

NBC (1995)

Simple Procedure

Reference Wind Speed

Gust Effect Factor

Detailed Procedure

Reference Wind Speed

Gust Effect Factor

X-Breadth (Wx)

Y-Breadth (Wy)

X-Natural Frequency(Nox)

Y-Natural Frequency(Noy)

Damping Ratio

Building Height

Exposure Category

Include Topography Effect

Hill Shape

2-D Ridge or Valley

2-D Escarpment

3-D Axisym. Hill: 3-dimention axisymmetrical hills

Building Location: Building Location in case 2-D Escarpment

Upwind

Downwind

Hill Height: Height of the hill or the difference in elevation between the crest of the hill and that of the terrain surrounding the upstream

Hill Length: Distance upwind of the crest to where the ground elevation is half the height of the hill

Crest-Building Distance (x): Distance from crest to the building site

Load Evaluation Using Force Coefficient: Determine whether to calculate load using wind force coefficient.

Eurocode-1 (2005)

Terrain Category: Exposure category

Friction Coefficient (Cfr)

Fund. Basic Wind Velocity (Vb,o)

Directional Factor (Cdir)

Seasonal Factor (Cseason)

Turbulence Factor (KI)

Building Height (h): Automatically inputted by the program

External Pressure Coefficients

Windward(A=10): Windward wind pressure coefficient for the area of 10m2

Windward(A=1): Windward wind pressure coefficient for the area of 1m2

Leeward Coef.: Leeward wind pressure coefficient

Lack of Correlation Factor: Lack of correlation of wind pressures between the windward and leeward sides

Parameters for Mean Wind Velocity

Consider Orographic Effects: Consider the increase of wind velocities over orography.

Orography Type

Building Location

Height of Topographic Feature

Length of Upwind Slope

Length of Downwind Slope

Crest-Building Distance: Distance from crest to the building site

Consider Effects of Neighbouring High-rise Structures: Consider the influence of higher neighboring structures on the wind velocities.

Building Height: Automatically inputted by the program

Average Height of Nearby Structures

Distance to the High-rise Structure: Distance from the building site to the neighboring high-rise building

Larger Horizontal Dimension: Larger horizontal dimension of the neighboring high-rise building

Height: Height of the neighboring high-rise building

Consider Raising of Displacement Height: For buildings in Terrain Category IV, closely spaced buildings and other obstructions causes the reduction in wind velocities.

Obstruction Height: Height of the neighboring structure or the obstruction

Upwind Spacing: Distance to the neighboring structure or the obstruction

Structural Factor: Gust effect factor

Along Wind Breadth

Along Wind Depth

Along Wind Natural Frequency

Logarithmic Decrement of Damping

Load Evaluation Using Force Coefficient: Calculate load using wind force coefficient

Force Coefficient

 

Eurocode-1 (1992)

Simplified Procedure

Roughness Category

Ref. Wind Speed (Vref)

Windward Pressure Coef.

Leeward Pressure Coef.

Friction Coef.(Cfr)

Topography Coef. at Building Ground Level Ct

Vertical Range for Ct

Force Coefficient (Cf)

Detailed Procedure

Roughness Category

Ref. Wind Speed (Vref)

Windward Pressure Coef.

Leeward Pressure Coef.

Friction Coef.(Cfr)

Topography Coef. at Building Ground Level Ct

Vertical Range for Ct

Gust Response Factor

: Gust Response Factor Calculator

Building Height (H)

Along Wind Breadth (B)

Along Wind Depth (D)

Along Wind Natural Freq (NI)

Fund. Flex. Damping (delta)

: Calculate Gust Response Factors

Force Coefficient (Cf)

 

BS6399 (1997)

Standard Method

Site Category

Building Type Factor (Kb)

Basic Wind Speed (Vb)

Mean Roof Height (Ho)

Seperation of Building (X)

Friction Drag Coef. (Cf)

Closet Diatance to Sea

Directional Method

Distance to Town Edge (Sa)

Altitude Factor (Sa)

Directional Factor (Sd)

Seasonal Factor (Ss)

Probability Factor (Sp)

Topographic Increment (Sh)

IS875 (1987)

 Standard Method

Basic Wind Speed

Terrain Category

Building Class

Friction Drag Coef.(Cf')

Risk Coefficient

Class of Structures

Risk Coefficient (k1)

Include Topographic Effects

Topographic Factor (k3)

Vertical Range for k3

Taiwan (2002)

Site Category

Shape Factor

Wind Load Direction Factor

Enter the loading direction and the magnitude of wind load to be applied.

Scale Factor in Global X: Scale factor to be applied in GCS X-direction

Scale Factor in Global Y: Scale factor to be applied in GCS Y-direction

Z-Rot: Scale factor to be applied in torsion about GCS Z-direction

Note

It is activated only when Japan (Arch, 2004) is selected.

Additional Wind Loads

Enter additional wind loads that the auto-calculation does not take into account.

Press to enter the stories to apply additional wind loads and the magnitudes for each direction.

: Display Tables and Graphs in a spreadsheet form for each loading direction and component of the auto-calculated wind loads.

Component: Assign the wind loading direction for a graphic display

Select Profile: Select the items to be displayed

Story Force

Story Shear

Overturning Moment

: Display a spreadsheet Text Output file showing the wind load calculation process. Text Editor is automatically executed.

: Apply the auto-calculated wind loads to the model.

Note
Refer to the relevant code for details regarding the wind load calculation.