Temporary Structure in Florida and California 1

[ThomasH]

Hello everybody
I asked this question some time ago but now the project has "woken up" again and now I know the locations.

It concerns a steel frame "box", four beams forming a rectangular floor (2.5 m x 6.0 m), four corner columns (total height 2.8 m) and four additional beams forming the roof. There are some additional secondary beams in the floor. Everything in RHS sections.

It's an exhibition monter with glass walls and there are a few of these "boxes" designed for the European market, using Eurocode etc.

The governing criteria has, so far, been overturning of the empty box for windload. One possible load situation is people and a few tables and chairs, so basically empty.

Now the client wants to do this in the US. Florida, high windloads, and California, possible earthquakes. I hope that somebody might be able to give me some ideas regarding requirements.

The duration for the exhibition is max two weeks. It's mobile but for each location we have max two weeks.

California, is earthquakes even valid? Especially for a one storey building. I am not worried about the forces but I don't think the current design will meet requirements regarding detailing, ductility and testing.

Florida, huge windloads. It is designed for high windloads by European standards, but Florida is worse. But a hurricane does not appear just like that. Would it be allowed to assume that we can ancor the "box" to the ground or even move it indoors if a hurricane warning should happen?

Is it completely out of the questing to have calculations according the Eurocode accepted for this situation? I have actually used FEM-analysis and modelled the sections with shell elements for certain reasons.

I have read in the IBC that for this type of sructure a permit from a building official is required. If anybody could perhaps share some info or experience regarding what that means for this type of structure? It would be very much appreciated.

Input is, as always, appreciated

Thomas

 

[JAE]

In the US, for short duration loads, we refer to ASCE 37 - Design Loads on Structures during Construction (

https://ascelibrary.org/doi/book/10.1061/9780784413098)

This provides reduced wind speeds for temporary structures - depending on duration.

It also mentions seismic but not sure it dives too deep into it. ASCE 7 (

https://ascelibrary.org/doi/book/10.1061/9780784414248a)provides

guidance on both wind and seismic loadings (in the commentaries)

You are intuitively correct that for 2 weeks duration both wind and seismic have significantly different (and reduced) statistical design magnitudes.

 

[ThomasH]

@JAE
Thank you for the information. I will check with the client how to proceed and also check the ASCE 37.

One thing though, the second link did not work. Perhaps it requires a login to the site that I don't have?

Thomas

 

[r13]

Is this an outdoor exhibition mounter? IMO, the duration and statistics on environmental catastrophic events are of secondary concerns compared to human safety. In either event (earthquake, hurricane), the structure should be allowed to fail locally, but shouldn't be harmful to the occupants at the time of occurrence. Hope this simplifies your thinking process.

 

[ThomasH]

@retired13

Yes, it is outdoors.

I agree that human safety comes first. My main concern is what will be acceptable from a "building officials" point of view. The duration at each event is so short that if there is anything missing in the documentation the time to fix it will be nearly nonexistent.

Thomas

 

[JAE]

Try this one:

https://ascelibrary.org/doi/book/10.1061/9780784414248

 

[ThomasH]

@JAE
That works.

Thank you

Thomas

 

[hawkaz]

Neither Florida or California will accept Eurocodes. Both states have their own building codes- based on the IBC

 

[r13]

Thomash,

I think you misunderstood my point. "Earthquake or any nature disasters does not know when it shall return/occur", so we always prepare/design structures to meet its challenges. For permanent structures, on top of strength requirements, there are durability and serviceability requirements as well. For your project, you shouldn't bothered too much on the latter two requirements, IMO, you only need to demonstrate the strength and stability during such event, even with some members have failed, as long as no collapse, or completely blown away will be resulted from such failure. You do need to follow the local standard though. I suggest to consult the local structural engineers, especially acceptance in CA for design done by out of state engineers.

 

[JAE]

retired13,

Your comment confuses me a bit:

IMO, the duration and statistics on environmental catastrophic events are of secondary concerns compared to human safety.

EVERY wind or seismic load we apply to a structure is based on duration and statistics. They are derived from a statistical return period accepted by our industry.
A shorter return period (2 weeks in this case) or factored up a bit to account for multiple 2 week usages can certainly affect the risk-safety-probability of a full code-based event.

That is what ASCE 37 tries to convey and what I think is possible to use here in this person's situation.

 

[r13]

A precast manufacturer cast quite a few bridge girders on a river bank, and banking on the fact that the flood with 100 years return period had just happened last year. Cut the story short - the guy was bankrupted, and the worst flood had occurred 3 years in a row.

 

[phamENG]

And an astroid might hit Manhattan tomorrow. We all play the odds every day - fortunately our industry has a pretty well accepted set of them, though curve balls do happen.

I agree with JAE that ASCE 37 is the correct approach to this problem.

 

[EZBuilding]

I recommend discussing utilizing reduced wind speeds with the AHJ. In several instances, in my past projects, the AHJ has not allowed for any reduced wind speeds for temporary structures.

 

[JAE]

retired13, that precast manufacturer didn't understand a lick of statistics. And s&*t happens.

 

[r13]

The truth behind the story is simple, if the guy really understood the real meaning of "statistics", he won't put his fortune on believing the flood won't happen until another 99 years. So he would opt the less economical route - cast the girders in somewhere else and transport in, an inconvenient way but safe.

Duration and statistics are important factors but secondary to the "use" and "category" considerations - type of structure, who are the users, size (how many) of the gathering. To me, these are the most important considerations in level of design determination. Isn't that code philosophy as well - identify the object to be protected, then determine the level of protection based on nature event reoccurrence period?

In my response, I've stated very clear, for short duration structure, there are ways to alleviate the design pain, but the strength. I would hope I am in line with code takes on this. Sometimes it pays to be overly cautious, this is the time - for efforts to stop the spread of coronavirus.

 

[phamENG]

retired - I don't understand how you're alleviating the design issues if you're still making it strong enough to withstand the extreme event. Can you elaborate on that some?

And as for coronavirus - that was in poor taste. I apologize. I've deleted it - I in no way meant to minimize the risk or imply we shouldn't use the utmost caution. Quite to the contrary. I only meant that there are always risks, no matter what we do and what steps we take - it's all about determining the limits of what's acceptable. I think we agree on this.

 

[SlideRuleEra]

Agree with JAE about using ASCE 37.

In Florida, there is another step to take (if possible) that will greatly reduce the odds of a high wind event. Do not schedule the event in July, August, September or October, prime time for hurricanes and tropical storms:

http://www.SlideRuleEra.net

 

[Ron]

@SRE....Yep. You nailed it as usual!

 

[r13]

pham,

I think some durability and services consideration could be relaxed somewhat, or ignored, due to the short duration of existence of this structure. Also, as mentioned before, even some members may not satisfy the strength criteria, but if the failure of these members will not cause the structure to collapse (verified thru analysis and judgement), so, a hinge here, a hinge there, and an excessive deflection on roof member but roof stays, I would say the design is acceptable, because it is harming nobody during the event, and is not required to continue its function after.

 

[phamENG]

Got it. Thanks for expanding on that.