Seismic Forces on Suspended Equipment 1

[Zeke]

Thank you for helping me with the previous thread. Now I have a situation with a conveyor belt system supported overhead from the roof joists of a warehouse. I know the forces on this will come from the roof, but how do I treat the swinging action on the conveyor.
I cannot brace it against anything, so the supports must be very stiff. How much deflection is acceptable? Also, do I need to analyze the entire warehouse, or can I just find the local forces only?

 

[Qshake]

The analysis of the suspended equipment is the same as equipment anchored on the floor of a building. The only mass of the system that is involved in the dynamic excitation is from the conveyor's own mass and the natural period of the suspended system. Thus you need only look at the support system for loads to the support. This assumes, of course, that the conveyor supports aren't part of the building's lateral force resistance.

Never say never. There are many devices (struts) available to absorb the energy during a seismic event. Check with Taylor Devices and others for more information. Also check out the piping industry as many of these suspended pipes use so-called anti-seismic struts to mitigate problems as well.

If your going to be working in this area, you may want to check out a few of the titles available from FEMA/NEHRP on seismic design guidelines, rehabilitation, and non-structural damage mitigation.

Good Luck.

 

[Zeke]

Thank you for the help, Qshake. I looked into the FEMA and NEHRP websites and couldn't find info on publications specific to my needs. I did get the SEAOC Blue Book and it is very helpful, but what I really need is a specific design example. I looked into the SMACNA for loads on suspended HVAC and similar, but to no avail. Do you have further ideas for example problems?
My suspended conveyor is attached to an 8 inch tilt up wall at one end and a vertical support at the other. I feel this helps for displacement, but if the wall anchors are overloaded, I can put some diagonal hangers in to resist the load. Am I on the right track?

 

[Qshake]

You're right on track. I suggest that you check out the UniStrut website and choose literature and then the seismic product information catalog. This is a PDF document that shows the framing including diagonals and has examples too.

Good Luck.