Time History Load Direction Combinations

[LoneStarEngineer]

I have an elevated concrete platform and I am researching on performing a time history analysis for the structure. The equipment manufacturer has provided a set of dynamic loads at the rotor support points for both horizontal and vertical directions. I have assigned sine functions for vertical loads and cosine functions for horizontal loads. I have three machines, two running at the same frequency and the 3rd one running at a higher frequency. I also have cosine functions with 180 degree phase angle for a separate load case.

If I have loads in X, Y and Z (X and Z being the horizontal directions), What time history load directions are combined together within the same load case? Are the loads in each direction analyzed separately and the response checked against the allowable limits or do I have to consider combinations of horizontal and vertical loads?

Is there a good reference on which time history load directions need to be considered/combined together for a load case? Appreciate any inputs. Thanks.

 

[JoshPlumSE]

It's not so much a load "direction" issue as it is a machine phase issue, right?

If machine 1 is running then it produces a certain set of cyclic loads. If machine 2 is running, then it produces a different set of cyclic loads. You may have to create a load combination where these machines are in phase and one where they're running out of phase.

 

[r13]

When checking against the limit, most likely you shall check the combination of concurrent effects that occur in the same plane.

 

[LoneStarEngineer]

Thanks Josh. I have my combinations set for in phase and 180 degree out of phase load case. I have two load tags like below. But I am wondering if I need to create different load tags for each direction of loading. For in phase condition, my thoughts are, inserting all the load functions acting in different directions under a single load tag would create a weird load angle.

And for example, if I am comparing the displacement amplitudes against the required criteria, then combining all load directions together would not give the maximum value that would occur compared to the case where I have set each time history load tag with one load direction each. Maybe I need to run multiple scenarios where I have just horizontal, vertical and combination of horizontal-vertical cases. And then another set with the phase difference...