Navigation:  Model Geometry > Editing Model Geometry > Element Local Angles

As discussed previously, members and shells have a local axis system that adopts a default orientation when the member or shell is first modeled.  

 

For a refresher on the default member local axis system, refer to Understanding Model Geometry > Members > Member Local Axes.  

 

The following diagram shows how typical steel sections are oriented on that default local axis system:

 

 

But there are times where a member needs to be rotated about its longitudinal (local x) axis to take on a different orientation, such as a channel with the flanges pointing downward or a WT with the stem pointing upward.  This is the purpose of the Modify > Member Properties > Element Local Angles command.

 

The default orientation represents an Element Local Angle of zero degrees. To understand how a positive Element Local Angle will affect a member, envision holding the member in your right hand, so that your right thumb points in the direction of the local x axis.  The natural curl of your right fingers indicates the direction of rotation due to an Element Local Angle.  

 

So when viewing the diagram above, assume the local x axis points into the plane of the diagram.  To rotate the channel so the flanges point downward, you would apply an Element Local Angle of 90 degrees.  And to rotate the WT so the stem points upward, you would apply an Element Local Angle of 180 degrees.

 

Note: Element Local Angles must always be specified as positive values.  So if the goal is to apply a rotation of -90 degrees, use 270.

 

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The concept of Shell Local Axes also applies.  When modeling many plates, it is very useful to have them all oriented in the same way, to make it easier to interpret results.  We have already seen a command called Modify > Reverse Node Order for Selected Elements that can be used to flip a plate over so that its top becomes the bottom and vice versa.  But what if there is a need to turn a plate so that its local x axis corresponds to the local x axis of a neighboring plate?  That is where Modify > Member Properties > Element Local Angles can be used, because is specifies a rotation of the shell local axes about the normal (local z) axis.

 

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