4 story wood building with steel beams and columns at the fi

huangyhg

4 story wood building with steel beams and columns at the fi
i am designing a large 4-story wood residential building with wood stud walls and wood truss floors. the half of the building at the first story is parking garage, framed with steel columns and beams which support the wood structure above. my question: is the steel frame needed to be braced by itself, such as using moment frame? since the floor truss will sit on the top of the steel columns and beams, i am concerned that if the steel frame can be braced by the plywood floor diaphragm above. any comments appreciated, thanks in advance!
if you are asking about span bracing, the wood trusses and flooring will suffice.  if you are asking about overall lateral load resistance, you'll have to either use a moment frame or provide some type of shear wall/ cross bracing.
i agree with ron here, but i am surprised that the first floor is not pt.  depending on the footprint, and the larger the better, pt should be more economical.
mike mccann
mmc engineering
thanks for your reply, ron. my question is about the stability of the whole steel frame. the overall lateral load resisting system of the building will be the wood stud shear walls in other parts of the building. my concern is that if the lateral loads acting on the steel frame can be transferred to the wood shear walls by the floor diaphragm since the diaphragm and the steel frame are separated by the floor trusses. if i use moment frame or cross bracing for the steel frame, the building will have two different lateral load resisting systems and i have to use the smaller r value, i don't know if i really need to do that.  
hi, msquared48, what is pt? you mean pressure treated wood? thanks
pt is post-tensioned concrete.
it would have to be a huge residence for pt to be economical, i would suggest a normal reo slab would be more functional for the builder, he probably get the same guys to do the 1'st floor that he will get to do the sog.   
when in doubt, just take the next small step.

the floor is 3/4" plywood sitting on the wood trusses or i joists. concrete is not an option.   
fire resistance??
if this is a residence, unless it is bill gates' house, pt will not be more economical.  
however, if it is  a decent-sized multi-family "residence", you should consider replacing the first floor framing with pt.
whatever works though...
mike mccann
mmc engineering
have seen a lot of this type of construction using precast hollowcore concrete plank at first floor above grade...then wood construction up from there.
neffers