Floor Diaphgrm

I modeled a structure with plate element for slab and shearwall with surface element in addition to member element to beams and columns. When I do analysis for SEISMIC as per IS 1893-2002 is it necessary to input the Master/Slave node or FLOOR DIAPHRAGM  as the slab is modelled as plate elemt? It is bit confusing. The very purpose of MASTER SLAVE is to make the diaphragm action when the slab is not modelled as plate element. This is what I understood. It it correct or not?

When I tried analysis the 4 warning message comes as FLOOR DIAPHGRAM is not there.

Kindly explain to understand the concept clearly?

T.Rangarajan

  • If you model the floor slab using plate element in STAAD.Pro, the behaviour of the floor slab will be similar to a “Flexible Diaphragm”. If you
    are happy with this behaviour, you do not need to add any more command in  STAAD.Pro. The rigid floor diaphragm assumption may not be appropriate if a relatively narrow building has closely spaced shear walls (i.e. the shear walls are stiffer than the floor diaphragm).  In the case of a low rise building, the floor diaphragms may be flexible compared to the shear walls as in light wood framed construction.  For long narrow buildings with deep beams the rigid floor diaphragm assumption has to be evaluated carefully.  The presence of a slab opening for elevators or stairs can weaken the floor diaphragm action.  Wood and metal decks without concrete fills may not be modelled as rigid diaphragms unless the floor system is braced properly. If you want to consider the floor are behaving like rigid diaphragm, you need to use rigid floor diaphragm commands in STAAD.Pro. 

    You can upload the model where you are getting warnings. I'll check that.