Siesmic Loading on ducting/piping 1

[GB1000]

Hi,

I've been instructed to perform siesmic loading on ducting and pipework which is already built.
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The existing detail is basically two M12 rods which hang from for above slab supporting the duct. the connection of the M12 rod is basically fixed in to the slab providing a rigid connection using Hilti products.

My question is, providing the lateral force times the lever arm to the support (bending moment) is less than the bending moment capacity in the M12 rods. is this sufficient? Most guids I'm reading appear to show actual siesmic bracing at 45 degrees. Does anyone know the answer and where I can look for it?

G

 

[DSB123]

Vertical rods are totally inappropriate to resist seismic lateral loads. cross bracing is required.

 

[KevinNZ]

You did not say how big the piping was. Obviously M12 bar is too small for very larger pipe, may be OK for small pipe. Threaded bar is not a good details for side loads. Some conservative load factors are recommended.

 

[12345abc6ttyui67]

Does the ducting actually need to resist the seismic load, or can it, and the hangers, just sway? More a question for your pipe stress guys.

 

[atrizzy]

Many codes and prescribed approaches for this type of work don't allow rods in flexure to resist seismic restraint loading.

 

[GB1000]

Thanks guys, yes I did some more research on this and it appears got hangers are not a good idea. There we end up using diagonal struts to resist the lateral forces.

 

[JackRob]

As noted above, hanger rods for mechanical are not meant for bending. Diagonal strut bracing with stiffeners on the verticals is quite typical, spacing would depend on the piping size/weight/function.

There are a lot of good resources for mechanical seismic restraint design.
SMACNA has a code guide and industry standard. FEMA has a booklet.
A lot of suppliers also have great resources, such as TOLCO, Gripple, Unistrut, Kinetics, just to name a few. All free literature on their website for download.