Wind load generation
WIND LOAD Z 1. TYPE 1
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10 ft, the second from 10 ft to 30 ft, and so on. EXPOSURE factors, which are magnification or reduction factors for the resulting generated loads should be specified if their value is different from 1.0. Here, all nodes between 0 and 75 feet are assigned a value 1.2.
LOAD 1 DW
The second part of the command consists of the actual load application and is done through the WIND LOAD command as shown above.
Question :
What is the significance of the TYPE command and the number that follows?Answer :
STAAD permits the definition of several different wind loads, each with certain characteristics. In order to distinguish the wind load having one set of characteristics from another wind load with a different set of characteristics, each wind load is identified using a TYPE command followed by an identification number. In other words, the TYPE command and the number are entirely a creation of the user. They are not terminologies that the user will find from any code or handbook that provides guidelines on loading for structures. The advantage of this feature is that the user is now able to communicate to the program information such as that the wind pressure is different at different heights, the structure has openings at certain heights and so on.STAAD.Pro Training Manual – Advanced Topics
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Question :
What is Wind Intensity?Answer :
Wind intensity as required for input in STAAD is merely the wind pressure in units of Force per unit area. The user is required to compute the pressure from any coefficients that codes require.Question :
Does the wind load command in STAAD take into account any wind codes like ASCE 7? Does it take into account the drag factor, or shape factor for different shapes like angle, channel etc.Answer :
WIND LOAD generation in STAAD is not based on any code. It also does not take into account any of the other factors you mentioned. It is based purely on the concept of influence areas of nodes and multiplying them by the user defined wind pressures for the respective heights. Any reduction or magnification of the resulting force is achieved by multiplying the generated values by exposure factors for nodes.Influence area of a node is defined as the region surrounding a node over which any wind pressure acting over that area is transmitted entirely into that node as a concentrated force.
Influence area is equal to influence length multiplied by influence height where:
influence length is half the distance from the joint to the joints to the left and to the right of the joint and
influence height is the distance from the joint to the joints at the top and to the bottom.
Multiply the influence area of each joint by the wind intensity and the exposure factor for the joint. This will yield the concentrated horizontal force for the joint. The exposure factor becomes useful for situations where the entire panel area is not effective due to the presence of openings or needs to be magnified due to a curvilinear shape of the load bearing panel.
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Question :
If I have wind speeds from different directions acting on a tower having (round shaped) discs fitted to it, how can I make the software take the discs into account which are also exposed to wind?
Answer :
The influence area calculation will work correctly if and only if the exposed area is parallel to one of the global planes. A region which is curvilinear in shape cannot be handled by the program.Question :
Can the wind force be generated in the Y-direction?Answer :
No. Wind forces can be computed for horizontal (X and Z) directions only.Question :
What if the windward face of the structure is inclined to the X and Z axes, viz., not perpendicular to X or Z axes?Answer :
The feature works best when the panels are parallel to one of the global planes. The program does have some capability forgenerating loads on inclined planes too. However, if the user finds the results unsatisfactory, other load generation methods like the
"ELEMENT LOAD JOINTS" option may be used.
Question :
What influence do finite elements have on wind load generation?Answer :
The presence or absence of elements, along or perpendicular to the direction of wind has no effect on wind load generation. Wind load generation is possible only with panels surrounded by members as described above. If the panels are already defined using plate elements, apply the load using the ELEMENT PRESSURE option instead of using wind load generation for those panels.STAAD.Pro Training Manual – Advanced Topics
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Question :
I have three questions. 1) How can I tell STAAD that the load is acting on the LEEWARD side and not on the WINDWARD side of the building? 2) How do I specify that a load acts from east to west instead of west to east? 3) How do I specify a suction load instead of one which bears against the structure?Answer :
The command syntax accommodates all of the above. For example, along the X direction, the following four types are allowed.WIND LOAD +X +f WIND LOAD -X +f WIND LOAD +X -f WIND LOAD -X +f
See the figure below for the meaning of the four commands.
X or Z - f X or Z -X or -Z - f X or Z
X or Z
X or Z + f -X or -Z + f
X or Z Y
Y
Y
Y
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Question :
Can STAAD perform wind load generation on open-lattice structures?Answer :
In STAAD.Pro 2004, the wind load generation facility has been enhanced for generating loads on open structures too. These are structures like electrical transmission towers, in which the region between members is “open” allowing the wind to blow through.For those, the program first calculates the exposed surface area of individual members of the model. Then, that exposed area is multiplied by the wind pressure and divided by the member length to arrive at a uniform distributed member load. It is assumed that all members of the structure within the specified ranges are
subjected to the pressure and hence, they will all received the load.
The concept of members on the windward side shielding the members in the inside regions of the structure does not exist for open structures.