elevator machine room structural slab

huangyhg

elevator machine room structural slab
i'm faced with a new (to me) concept. designing a 'structural slab' for support of traction elevator machinery as opposed to using steel machine beams. i have a steel-framed building and an elevator bank of 6 shafts (3x2 back-to-back). do i just need to design a thick concrete slab spanning to the steel beams? can i put steel beams between the individual elevators? can i use metal deck to support the wet concrete, or does it need a flat soffit? do i need to document the holes in the slab, or can i just say "refer to elevator shop drawings." any other tips or suggestions would be appreciated. thanks.
mark daski


1.  the required loads are given by the elev. manufacturer, and normally a thick concrete slab is the way to go.  
2.  i would think that you would need to put steel beams between the elevators to provide support for the guiderails along the sides of the elevators.  normally the elev supplier will dictate a max spacing between the guiderail supports, and when you have side by side elevators, there is no floor to attach the guiderail to, so some beam will be needed.
3.  i dont see why a flat soffitt would be needed, so it could be done this way, but check with the elev. supplier.  depending on the weights and spans, this slab could be 6-8" thick, so metal deck might have to be fairly thick to handle the loads.  
4.  you need to account for the holes in your slab design, but i wouldnt call the placement out on your drawings. just refer to the elevator shop drawings.  once you get these, you may find that the hole pattern you assumed is different, and may need to add rebar, so be conservative in designing the slab.  
i just spoke with a rep from thyssen-krupp. he said i could use metal decking--there's no specific need for a flat soffit. it will probably need to be shored up in any event.
i do have elevator seperator beams at every floor for rail attachment. he said the steel beams used to support the slab must not infringe on the shaft width x clear overhead dimension.
since we only have 4" between elevators (hss 4x12 seperator beams), if i need a w36x300(!) to support the machine slab, this beam must be entirely above the "clear overhead dimension" on the elevator shop drawings, thus pushing the entire machine room higher.
mark daski


fwiw:
we usually use 3" metal deck as formwork to contain the wet concrete during placing, but then design a conventionally reinforced concrete slab as the floor structure, ignoring the composite effect of the decking.
10" to 12" thick slabs are not uncommon in elevator machine rooms, depending on the layout.  
agree with strguy11, be very conservative in your design. elevator suppiliers have ways of just arbitrarily changing their requirements, or pointing out some obscure foot note in the information they gave the architect that they expect everyone to have read and complied with exactly.
i definately would not locate blockouts or embeds for the elevator suppilier. they are notorious (around here) for trying to blame others when they are not located exactly.