Equipment Suspended from Floor Beam

[Eng_Struct]

I have mechanical equipment that is suspended and needs to be supported from the third floor framing. The equipment weight is about 40kN and the framing has a rectangular footprint of 4775mm X 1030 mm.

I have put together a concept for the system and will like to get some insight. Everything in blue is new and everything in red is existing. Below are the particular items I am concerned with:

1. Item "A" labeled in the image: HSS hanger to the floor beam bottom flange connection - I have considered steel plate tabs welded to HSS and bottom flange separately and shown a bolt in shear to pick up the hanger. I know this detail will work but it is just that I do not see redundancy in this type of connection. Any thoughts/ideas on details that might be more robust than what I have considered?

2. Item "B" labeled in the image: equipment platform beam attached to HSS hanger - I have considered a shear tab with a stiffening plate to pick up the support beam. The HSS is shown to extend past (roughly 50mm) the bottom flange to ensure that the detail does not end up buckling the web at the free end. To provide extra strength, I have included a "cap plate" at the bottom. Any Watch-Its for this detail?

3. Items "C" & "D" labeled in the image: lateral bracing in the short direction - I have considered two options: knee braces item "C" and single diagonal brace item "D". I like the knee brace option but the problem is I end up with excessive displacement in the short direction at the bottom (HSS will be designed to sustain moment from knee bracing). To control platform displacement, I came up with a single diagonal but I am not sure if attaching it to the floor beam as shown in cyan color is appropriate. Note that I do not want to attach the bracing to HSS at the top because it will put the top hanger connection to work in both vertical and horizontal directions. Thoughts?

4. Items "E" labeled in the image: lateral bracing in the long direction - I have sufficient room to put an inverted-V bracing as shown. The challenge is that I can only put the bracing on one side in the long direction as the owner needs to be able to access/service the equipment from the other side. I will be providing horizontal bracing at the platform level to carry the load to the side where the bracing is. I think this should work but will like to hear other thoughts.

Thanks

 

[dijonnaise]

1. Can you weld the HSS hangers to underside of existing beams?

2. This looks totally fine to me! Edit: It looks like you don't have the gusset plate connected to top of the beams - I would connect those directly so that you're not engaging the bottom of the HSS hanger in moment.

3. I would use the diagonal brace. The knee brace is likely more expensive or at least in the same ballpark due to the increased number of connections, will result in higher deflections and more moment in the HSS hangers. Diagonal brace connection at the bottom beam looks fine to me. I'm not quite understanding the comment about "putting the top hanger connection to work in both horizontal and vertical directions".. You've intuitively drawn a long horizontal leg to the gusset plate - that's where the horizontal force is going to transfer from the diagonal and into the beam above. Since the gusset will likely not deform significantly and the hanger connection is comparatively flexible, it won't engage the hanger connection in significant shear. That said, I've suggested welding the hanger directly to beam in point '1' above which might assuage your fears a bit.

4. If you only have a brace on one side you'll have to consider that since your brace line is eccentric the center of gravity of the platform, any lateral force (quake, likely) will be resisted both by the one-sided (resisting the total horizontal load) and by the short-side braces resisting a force-couple torsion caused by the eccentricity. If you have this modeled in 3D you may already be observing this behaviour, but good to keep in mind when evaluating the capacity of the short side braces. Could get some significant deformations on the long side if the braces aren't stiff enough.
Another thing to keep in mind is that the chevron bracing will kick a vertical point load into the new blue beam at the midspan connection. Good to check for unbraced bending.

 

[Eng_Struct]

Thanks for the feedback, dijonnaise!

This is really helpful.