Modelling the cross aisle direction of a steel selective rack for model analysis
 

I'm trying to model the cross aisle direction of a steel selective rack for model analysis. The rack is simply set out with some uprights (column) supported by some cross bracing that is connected eccentrically.

The model only had to be 2-D, but to use the correct cross section I had to use a 3-D element (beam 188) as the 2-D beam elements do not allow this. I was then just going to restrict the rotation in the x and y direction and displacement in the z direction so its like a 2-D analysis but not sure if that would work.

I'm been struggling to use the program and I am having some difficulties which are:
* Adding mass to represent the crates. I know there is mass element 21 but am I just able to add it to a key point and it will automatically join with the uprights.. Or do I add it like a concurrent node
* The bracing needs to be connected to the uprights so that bending is still allowed in them. I am not sure which joint is best as none of them look suitable and how I would connect both bracing to the same node as mentioned before the bracing is eccentric.
* I am going to do an earthquake analysis using a program Anseismic that works with classic, I am looking at rocking structural systems so need a way to represent the base plates yielding and the structure rocking in analysis. I can't just use a spring element as the plates hit the ground and don't compress like a spring. I saw a combination element 41 but did not quite understand from the manual if it would assist in the analysis.

Any help would be great thanks.