Horizontal loading to Internal Piperack Structures

[EireEng]

I am working on a large industrial building where there are some significant piperack/trestle structures suspended from the underside of roof level,
The building will be fully clad, so these are internal structures,
They are large structures made out of light unistrut framing, they support mechanical and electrical services within the building,
For scale, some of these are 3.5m (11'5") tall (suspended down from the roof steelwork), 3.0m (9'10") wide and run throughout the length of the structure, circa 150m (490ft) long

My query is this;
I would like to hear your opinion on whether these piperacks should be designed for horizontal loading,
If so, have you experience with designing large internal structures/equipment for wind pressure due to internal wind loading (as you would apply to a partition wall say)or for a notional horizontal load ?
Have you any recommendations on horizontal loading to apply for the design?

There are no horizontal loads being applied from the pipework/electrical cabling that they are supporting, however, I believe it prudent to apply a notional horizontal load (be it from wind or other) to justify the stability of these large hanging structures, however some others I have spoken to believe otherwise,

Appreciate all thoughts on this,

Regards,

 

[JoelTXCive]

1) A quick sketch or photo is worth 1000 words.

2) Are the fluid pipes gravity flow; or are they pressure pipes with possible thrust forces? (The wind load will likely be chump change compared to thrust forces if you have them.)

 

[BAretired]

Wind pressure is one consideration. Seismic forces are another. Both should be considered in accordance with the appropriate building code.

BA

 

[JoshPlumSE]

I would like to hear your opinion on whether these piperacks should be designed for horizontal loading,

I think they should be designed for some form of seismic loading. It may not be much, but it will likely required some horizontal struts or such.

 

[Liam Nesson]

My first question would be a heavy industry building or a light industrial building? If heavy industry im surprised your using unistrut. I do see some crazy stuff done with unistrut and wonder if they have any slenderness requirements.

Check with your mechanical engineer
Are there any guides or anchors on the pipes? And what deflections can they handle both vertical and horizontal? The pipe racks are essentially supported on a building that likely has larger drift and deflection limits than they can handle, especially if they are fixed to equipment that doesnt deflect much like tanks or pumps. The differential movements will create loads. If no guides or anchors then you likely have to consider friction loads from the pipes as the building moves, thats if you brace it up. There may be justification to keep everything flexible given building movement, but then stuff may be swaying during storms which means you could be getting calls from your client.

If memory serves me correct, there may be justification not to brace cable tray in low seismic zones, not too sure for piping. I would have to go searching to find that guidance.

Doubt i would consider wind for an internal rack.

There are pipe rack design guides out there too that you may be able to use to support any bracing you want to add

 

[EireEng]

Firstly, thanks for the quick responses here guys
To elaborate and hopefully clarify some of the points raised;

The project is not located in a seismically active region, in fact, there is no requirement to assess the structure or applied elements for seismic actions in this country,
There are no large bore piping on the service racks and I'm told that there are no thrust forces or anchor points along the runs for the smaller pipes either(however, that is TBC... I will confirm)

It would be considered mid-heavy industrial, and yes typically I would design this scale of pipe/cable rack in structural steel, but I am not the design Eng in this situation (contractor led design - hence the light unistrut framing). I am acting as client structural rep on this particular project,
The unistrut frames are modular - typically no more than 6.0m (19'8") in length

I appreciate that the racks should of course be designed to the appropriate building code (in this case Eurocodes), however, there is no clear guidance on the application of internal pressure/forces to this type of structure as far as I am aware - that's why I'm here

Really the query is; what is considered the most reasonable/safe lateral load to apply to a hanging structure of this nature to ensure the stability of the modules/frames themselves and their connections to primary structure

Again, thanks for your thoughts on this

 

[human909]

I meant to reply earlier. But I think I got distracted by actual work. While your area might not have seismic requirements low seismic loads are reasonable point of reference for lateral restraint IMO.

My standard approach to most small structures with machinery or people is 10% of the dead/live load. I use this because that is our seismic guidelines and I generally don't find it onerous for small structures. I can be comfortable that the structure will be rigid and vibration free for most needs.

Really the query is; what is considered the most reasonable/safe lateral load to apply to a hanging structure of this nature to ensure the stability of the modules/frames themselves and their connections to primary structure

For something hanging that isn't sensitive to vibration or some movement I would be happy to relax my 10% to 5% or a minimum maintenance load say 0.5kN of some maintenance worker performing work on the pipe rack/cable tray. Ultimately you need to use your own judgement to a certain extent. Some times we need to leave the codes at the door and work out something sensible.

Normally I've also used 10% for hanging structures. Again I generally don't find this onerous on lateral bracing requirements.

 

[EireEng]

@human909

Thanks - this does seem sensible to me and I had suggested in my reply to the designers that the frames be designed for a notional horizontal load to ensure their stability/robustness
As far as I can see, there are no hard and fast rules for quantifying the magnitude of this applied load (when not required by seismic code)

 

[dauwerda]

I'm not sure which codes/standards you need to follow, but ASCE 7 does assign minimum lateral forces for all structures. Section 1.4.2 (of ASCE 7-16) states:

1.4.2 Lateral Forces. Each structure shall be analyzed for the
effects of static lateral forces applied independently in each of
two orthogonal directions. In each direction, the static lateral
forces at all levels shall be applied simultaneously. For purposes
of analysis, the force at each level shall be determined using
Eq. (1.4-1):

F[sub]x[/sub] = 0.01W[sub]x[/sub] (1.4-1)

where
F[sub]x[/sub] = the design lateral force applied at story x, and
W[sub]x[/sub] = the portion of the total dead load of the structure, D, located
or assigned to level x.

Structures explicitly designed for stability, including second order
effects, shall be deemed to comply with the requirements of
this section.

 

[Liam Nesson]

Maybe just account for friction due to thermal or differential movement of rack / building versus equipment:

If you use 10% this would tie in nicely with human909's suggestion. As for nominal loads, Canadian code specifies 0.5% which is tiny for this type of structure.

 

[JoshPlumSE]

Liam -

That's meant to account for LONGITUDINAL expansion of the pipes. I believe the OP (and most of us) have been talking about transverse support of the pipes.

 

[Liam Nesson]

Fair enough.

 

[JLNJ]

Check out ASCE Chapter 13 - Seismic Requirements for Non-Building Structures. it exempts piping in SDC B from the provisions of the chapter. That's how you can use simple rod pipe hangers in most low-seismicity locations.