SAFE- Reaction Forces

[EngRon]

I have modeled a 30' transfer slab in SAFE 16 with gravity loads (from a 4 story building above). The gravity loads have been input by assigning loads to null beams and areas. However, when running the analysis, it produces some rather large joint reactions in the x and y direction. This seems odd to me as no lateral loads have been input. I have attached a screenshot and the safe model. Any tips would be appreciated. Thanks!

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1529437890/tips/safe_reactions_jchirv.pdf[/url]

 

[bones206]

I suspect the lateral reactions are due to boundary conditions overconstraining the model. It's analogous to a uniformly loaded pin-pin beam versus a pin-roller beam: The pin-pin beam will generate lateral thrust at the supports, whereas a roller relieves that thrust force and you don't get a lateral reaction.

 

[bones206]

Here is a simple example of a frame with all columns pinned, and then with two of the column supports modeled as rollers. You can see that the 202.5 lb lateral reaction disappears from all column bases once the lateral constraint is removed from the system.