Concrete Structure with Steel Roof / Joist Girder to RC Column 2

[ThorenO]

2-story bldg, where 1st and 2nd floor occupancy requires concrete and steel roof is preferred by the client. Building will have interior elevator/stair and exterior RC shear walls. What are the some of the pitfalls to look out for or suggestions to permit a steel roof with concrete columns. With the seismic roof shear relatively low, I am looking at 4-anchor embed/bearing plates at the top of the columns. The girders can be designed for a large axial force, but only in one direction. It the other direction, I am looking at some form of tie-joist, which can also be designed for an axial force that would brace the top of column and not permit a weak-beam/strong column buckling condition. Thanks for any feedback in advance.

 

[bowlingdanish]

and not permit a weak-beam/strong column buckling condition.

Wait, isn't that condition that you want for seismic? My knowledge is a bit thin.

And why can't you just have steel columns for the top floor? If the architect wants a consistent facade this can be achieved with tophats/cladding.

 

[KootK]

A colleague of mine did something similar a few years back. It looked a little odd but went together gret. Unless the floor plan switches to long span at the roof, I still feel that concrete all the way is cheaper but, at the end of the day, we have to rely on our contractor friends to tell us what's really most economical. We were initially worried about tolerance compatibility between the steel (beams in our case) and concrete. It ended up being a non-issue and I'd think that your topside connection strategy would eliminate most tolerance issues anyhow. Maybe just a healthy grout bed to provide for vertical adjustment. If your lateral system is concrete shear walls, you probably don't need to sweat any strong column / weak beam issues.

One thing that I like about the system in comparison to using steel columns is that you don't need to worry about that awkward condition where you're trying to generate a concealed, yet erectable, column base condition.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.