EQ direction

[jefferyr]

Hello,

currently I have two earthquakes records being applied to directions 1 and 3. If I wanted to rotate these, what's the easiest way? Do I need to rotate the nodes relative to the global axes, or is there a more direct method to do it?

Thanks,

jeff

[vesna]

Jeff,

For what angle do you want to rotate it?

[jefferyr]

Lets say the two earthquakes are still orthogonal to each other, but I want to rotate them relative to the longitudinal axis of the bridge. So, maybe a rotation of 30 degrees or 45 degrees, or better yet, a variable amount of theta degrees.

[vesna]

There is no way of assigning the earthquake that acts on the model with an angle between 0 and 90 degrees relative to the global axis.

However, there are two ways to assign the earthquake acting with an angle relative to the longitudinal axis of the bridge:
1. You can perform transformation of ground motion records from rotated axes to global axes and assign transformed ground motions to the global direction of the bridge.
2. You can set up the global axes to coincide with the directions of ground motions and define the model with respect to this coordinate system.

[jefferyr]

That's what I thought. I'll probably make a new tcl script that will take the old 2 accel records and make new earthquake acceleration records treating the old accel values as vectors and breaking them into new components to reflect the new directions. Is this the same as your option #1?

Thanks

[vesna]

Yes, that is the option #1.

[canim_ken]

Hi,
The other option is rotating the translational masses which is assigned in nodes to any angle you want.