Mixed Use System

[sedesigner06]

I have 260'x290' building consisting of 3 different lateral systems. Precast composite sandwich panels, masonry shear walls, & brace frames. Diaphragms are all flexible so am not to worried regarding one system attracting a majority of the load. Area is hardly no seismic so wind load is sure to govern.

Are there any other concerns with mixing this many systems within one building?

Thanks

 

[jdgengineer]

I would say it's generally not recommended as it becomes difficult to predict the performance of the building as a whole when you mix and match too many different systems. It would be wise to envelope the solution (i.e. maybe design diaphragm as rigid and flexible unless you are really certain the diaphragm is flexible) in order to make sure you have upper and lower bounds on the design forces to each system. I would generally want to have a little conservatism in the design as well do unpredictability in the system that may not be picked up with typical calculations. Assuming you use ASCE 7-10 you'll need to abide by 12.2.3.3 which will limit your R, Cd, and Omega to the least value in the direction unless you meet the requirements for the exception to design each line independently.

With all that said, in my area it happens frequently. In high-end residential design it's not completely unheard to have concrete shearwalls, wood shearwalls, and steel moment frames compromising the lateral system. Not in my opinion the best system from a structural perspective, but it is sometimes what the architecture demands.