5 psf Horizontal Live Load - Trade Show Structures

[Hedonism Bot]

I have a question about whether or not IBC 1607.14 applies to temporary displays like at a trade or auto show. I have been hired as a structural engineer by a marketing firm that specializes in trade/auto shows. Looking at previous engineers designs and the designs I see at shows, the code required minimum 5 psf horizontal live load is not being taken into account. The challenge of these designs is that they cannot be attached to the slab and so you get a 10-20 foot tall cantilevered wall that is stabilized from overturning with baseplates resting on the slab and added ballast. I'm not sure if IBC considers these things a wall or partition but I do know that the designs get impractical very quickly if the 5 psf is applied. I have been advised by an structural engineer who has worked in this space to design for the seismic load for stability. Anyone have any thoughts or suggestions?

 

[dhengr]

Hedonism Bot:
I think that at the very least, you have to have a long talk with the marketing firm about your obligations as regards the safety of the public and about meeting min. bldg. code req’rmts. I would ask them to get an E&O and liability insurance policy which would cover you as you did work under their direction and for them. Also, this is a little different situation than a product manufacturer’s usual self-insuring as relates to product design and manuf’r. This is not a permanent structure, but all the same, everyone remotely involved could end up being sued if anyone got hurt by one of these displays. How is this handled and are you specifically protected as a P.E., by the policy, in this situation? The firm has its std. business insurance coverage to protect its business operations, and all you may have is your P.E. license and assets to lose if anything goes wrong. Do you have any control over the manuf’r. of these displays, of their assembly and installation, or can you be blamed for errors there too? I do understand that this is a competitive business, but how do others handle these issues, do they have a P.E. doing this design or just a CAD monkey doing it? I’d probably want to talk with an attorney about this issue and your liability.

 

[SlideRuleEra]

...the code required minimum 5 psf horizontal live load is not being taken into account.
...cantilevered wall that is stabilized from overturning with baseplates resting on the slab and added ballast.

Have you calculated the overturning load (psf) the displays can withstand the way they are used now?
I like the other engineer's idea to come up with some established loading that can be used a basis for an "acceptance criteria".
The established loading used could be seismic, or perhaps derived from temporary loading requirements (ASCE 37).

http://www.SlideRuleEra.net

 

[BridgeSmith]

The first thing I would want to know is the source of the loading. Only then can a rational and reasonable load magnitude be determined. I assume these are intended for indoor use (even a mild wind gust would exceed 5 psf), so what does that leave? A person stumbling into it? A gust from someone opening a door? Air pressure from an HVAC system? Errant footballs?

 

[Settingsun]

It sounds like construction site fencing/hoarding without exposure to wind - at least the lower end of your height range. Is there a US code for those hoardings that give the 'people' loading requirements?

 

[Hedonism Bot]

Thanks for the thoughts guys. We do have a very robust E&O policy here. They have quite a bit higher policy than I am used to in the consulting world. Most of the larger shows require a PE stamp on the drawings for their shows. Coming from the building design world that I did, something like the 5 psf minimum horizontal live load rarely, if ever, controlled design of interior walls. In this space, however, that same load quickly becomes impractical to design for. A 5 psf load corresponds to a 60 mph wind on a 20' structure in exposure B. I don't think this is a likely case for interior temporary displays. For outdoor builds, we put stipulations on that require part or all of the structure to be disassembled if winds are predicted to be above 40 mph or we use the ASCE 37 if disassembly is not practical.

Let me put some numbers to how impractical the 5 psf live load is for these structures. Let's say we have a 15' tall x 20' wide aluminum frame wall with a fabric wrap that has a total weight around 300 lbs. We want to stabilize it with (3) 4'x4'x3/4" BP's that weigh 325 lbs each. The overturning moment is 11250 ft-lb. The stabilizing moment is 2650 ft-lb. So we need 8600 ft-lb additional stabilizing moment. Assuming the ballast acts 3' from the edge of the BP (this is where we will overturn) we need 2867 lbs of ballast total or 956 lbs on each BP. Even with these numbers there is no safety factor. Let me assure you that nobody is providing this much ballast on these structures and I am not aware of any failures with injuries from these type of displays.

I find myself in a grey area code wise. These shows require a PE's stamp, but the building codes were, IMO, not written with structures like these in mind.

Since I am the only PE in the company, these decisions are left up to my judgement. Thus far I have designed for the seismic forces in the area where the display is to be built with minimum of 25% g no matter the location's requirements and I also design to make sure the structure can rotate 15 deg without overturning.

 

[BridgeSmith]

Your reduction factors much be much more aggressive than ours - I don't come down to 5 psf until I'm down around 30-35 mph wind speeds.

Anyway, it sounds like these are going to be indoors. Again, where are you expecting the loads to come from? If you're looking for advice on what's reasonable loading, I think it has to start there.

Code requirements and compliance is a separate issue, and I'm certainly not the guy for that.

 

[JStephen]

From this link:

http://mromarketing.aviationweek.com/downloads/mro2018/PoliciesandTerms/18_Americas_DisplayRules.pdf

I find this statement, which appears garbled (?):
"3. Calculations are to prove that the stand is stable and capable of supporting the loads of anything
which will be supported i.e.: lights, speakers plasma screens etc. A nominal load should be
applied for wind (0.15 kN/m2) although this appears not to apply in the halls stands have been
affected by doors being open. A calculation should also be carried out for overturning this
assumed to be the impact of a person (0.75 kN) at a height of 1.5m above the ground."

The 0.15 kN/m2 looks like 3 psf.

That references this document:

http://mromarketing.aviationweek.co...mation-DISPLAYRULES/18_Am_IAEE_Guidelines.pdf

Which says:
"Structural Integrity
"All exhibit displays should be designed and erected in a manner that will withstand normal contact or vibration caused by neighboring
exhibitors, hall laborers, or installation/dismantling equipment, such as fork lifts. Displays should also be able to withstand moderate
wind effects that may occur in the exhibit hall when freight doors are open. Refer to local building codes that regulate temporary
structures."
But, I can't find anything in local building codes that regulates that.

I find references to: BS EN13782, which appears to be more related to tents, etc.

 

[TDGRAVY]

Hedonism Bot:
I'm in the same boat, designing an aluminum frame for a temporary interior trade show exhibit. I agree that IBC 1607.14 is the place to start (5 psf lateral). It would take a lot of committed people to generate 5 psf lateral load, pushing on the entire structure, but I think the 5 psf is a reasonable magnitude for internal pressure differentials on the interior of the convention center. Overturning really is the key issue. A few additional points I will make: first, to be conservative I'd like to assume the 5 psf lateral load can be applied both in the "X" and "Y" horizontal directions simultaneously. Is there any logical reason it shouldn't be applied simultaneously? Obviously, this does make the overturning worse. Secondly, in terms of seismic: my logic is that seismic loads need not be considered, given that this structure will only be up for a few days. My code reference for exempting seismic design is ASCE 7 Chapter 13, which provides exemptions for temporary equipment. I'm not aware of any other published standard that might address this situation any more specifically. ASCE 37 (Design Loads on Structures During Construction) doesn't seem to be particularly appropriate - the construction condition isn't of particular concern. Finally, I see that using a wide baseplate on the floor creates challenges for avoiding tripping hazards as well. If a 1/2" steel base plate projects a foot or two beyond the exhibit wall, and isn't otherwise "feathered out" to the main building floor or somehow barricaded off - it could be a hazard to people walking close to the walls and not paying attention to a projecting base plate. If the 1/2" thick base plate can somehow be restricted to the interior of the exhibit (and possibly a few inches on the exterior, if really needed), it seems like a plywood flooring substrate could be laid throughout the exhibit's interior to create a flush, no-tripping-hazard condition (the entry thresholds could have a separate ADA beveled threshold strip to get up to the +1/2"). Some kind of finished flooring surface on top of that. Obviously that additional plywood flooring is an extra cost and probably a hassle, but what else are you going to do if you can't anchor to the floor?

 

[WARose]

At the risk of getting somewhat off-topic....I've worked on similar type structures, and (if this is something re-used/moved a lot) a controlling load case can be when the thing is being moved around (i.e. stopping and starting). I checked one like that and it controlled over any kind of internal wind pressure. It just depends on how much it weighs. A light deal won't be a problem.

 

[CANPRO]

but I think the 5 psf is a reasonable magnitude for internal pressure differentials on the interior of the convention center

I think the "pressure differential" part of this is key to the discussion. Not familiar with the IBC reference, but a similar requirement is in the Canadian Building Code for interior partitions - I believe it is around 10 psf.

In order to get a pressure differential, you need have enclosed spaces. A bunch of free standing partitions in a large open area won't/can't separate two different pressures - and that would be my argument against the 5 psf.

Another reasonable approach would be to apply guardrail loads (50 lbs/ft) at a height of 4' above the slab.

 

[bridgebuster]

Hedonism Bot:

You never mentioned what you're going to display. Any nearby tradeshows you can go to in order to see how others do this?

 

[KootK]

I understand your difficulties with this but, still, I'd not be too excited about seeing my kids horsing around next to a 20' tall display board not even capable of the 5 PSF lateral. Any chance you can get what you need here by way of geometry rather than monster ballast. Plan cee shapes or sawtooths etc? I may never feel safe at winefest again.

In order to get a pressure differential, you need have enclosed spaces.

I question that. There are at least three factors to consider in the development of differential pressures:

1) Can air movement equalize the pressures on either side of a wall.

2) How quickly can air movement equalize the pressure on either side of a wall. If it's not very quickly, net pressures still need consideration.

3) How much net pressure inducing turbulence is involved in air movement equalizing the pressures on either side of a wall?

Obviously, we still design free standing exterior walls for a net pressure difference even though no part of that system is enclosed.

 

[CANPRO]

Kootk, I agree, I think any wind related load is delivered through a pressure differential, doesn’t neccesarily have to involve an enclosed space. My comment was more in the context of that code required load on an interior partition. 5 psf correlates to a wind speed of about 70 km/hr, so I’ve always assumed that interior partion load was due to net pressure differentials across an enclosing partition, and not due to being exposed to a direct gust of wind.

 

[KootK]

I'll buy that. Thanks for the explanation CANPRO.