Question about temporary structural loading. 3

[3doorsdwn]

I've got a structure I'm designing that will be in place about 4 months (only for 4 months). The thing I'm trying to decide is whether or not to use full lateral loads or something less. I know ASCE puts out a standard on this [i.e. ASCE 37]....my question is (for anyone who has this standard): does this standard address load magnitude vs. specific duration time? And (if this is addressed and you feel generous): what kind of magnitude are we talking for 4 months duration (approximately)?

 

[asixth]

What structural load are you designing for, gravity, wind? For temporary bracing elements I will only use a 100yr design event for wind opposed to the 500yr return interval which is usually designed for. This is specified in the loading code that I use. It would also depend on the type of structure that is being designed. If it is a structure that is likely to see it's design load during it's design life than I would not make any reductions other than the minimum which is specified in the code.

 

[3doorsdwn]

It's the wind load I'm worried about. Something that is going to be up in Southeastern Georgia in the summer months makes me worry about the possibility of everything from thunderstorms to hurricanes.

 

[msquared48]

Is this structure to be erected in August of 2012?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[3doorsdwn]

Is this structure to be erected in August of 2012?

Nope. June 2010....will be down sometime in September 2010.

 

[JAE]

Yes, ASCE 37 deals with load durations.

 

[Ron]

Keep in mind that many "temporary" structures that were built 20 years ago are still in service...design for that potential.

 

[3doorsdwn]

Yes, ASCE 37 deals with load durations.

So is it significantly less than the full amount for 4 months duration (if you [or anyone else reading this] have this reference)?

If it's close: the heck with it, I'll just use the full design loads. But if it's (say) half......it will justify me going out and buying the reference to read the fine print and get the load down exactly. (Where I'm working they don't have this on the shelf.....so I'm trying to brow beat my boss into getting it and this will give me ammo.)

 

[msquared48]

Ron:

For that matter, "temporary" barracks structures for the military built in the 40's are still in service today!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike,
That's exactly what I was thinking of. I remember many of those structures at Ft. Jackson, Ft. Dix, and Ft. Bliss.

When the base closings were going on, I couldn't help but think about all the new buildings that would be "abandoned", compared to the old ones that had served for so many years..such a waste. Big difference in benefit to cost.

Ron

 

[BAretired]

I agree with Ron and Mike. Design the structure just as you would a permanent structure.

BA

 

[msquared48]

When I was in the Corps of Engineers in Officers' Basic in Ft Belvoir, Virginia, they showed us plans of those wooden barracks - made during WWII.

On those plans, in bold letters, it stated that the planned service life of those structures was only five years. After that time, they were to be demolished.

The point is that things change, to include intentions.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[3doorsdwn]

The point that (in many instances) a temporary structure may wind up being permanent is well taken. But in my case it cannot be permanent because it blocks a main service route into a particular part of a plant. (And the expected duration will be noted on the drawings.....in fact, we are even referencing the letter from the client stipulating that it will not be up beyond a certain point).

So it kind of goes back to my question from before: for that duration, what kind of % of the max load are we talking? (Ball park for anyone that has this reference.)

 

[Ron]

3doorsdwn...there is not a single factor that can be applied. In ASCE 37, there's a factor for each of many different conditions. You'll need a copy of ASCE 37 if you want to try to apply it to your design.

I'm not convinced that it applies to your case. It is moreso intended to address temporary construction loads and exposed structural conditions during construction. There is a provision that includes "temporary structures" but my interpretation of that is such temporary structures as formwork or shoring, not a completed structure that is used for a short period of time.

Further, if you are in a wind area or snow area that is significant, the time of year that the building will be used will be critical to your design.

 

[msquared48]

How much liability insurance do you have?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JAE]

I'm away from my office right now and don't have access to ASCE 37 - I'll check on it but at 4 months the "downgrading" of wind force due to the supposedly temporary condition may not be all that much. ASCE 37, as others above have suggested, is really for structures used to facilitate construction of other structures.

In your case, the 4 months indeed might grow to 6, 8, or 800 months.

 

[3doorsdwn]

I'm away from my office right now and don't have access to ASCE 37 - I'll check on it but at 4 months the "downgrading" of wind force due to the supposedly temporary condition may not be all that much. ASCE 37, as others above have suggested, is really for structures used to facilitate construction of other structures.

In your case, the 4 months indeed might grow to 6, 8, or 800 months.

Well I appreciate it. At this point I'm starting to wonder if I'll need this to justify designing for full design forces.....(sort of the opposite that I was thinking before).

But it cannot stay up for 4 months [and really....people are already raising about it being up that long]. The plant would shut down if it stayed up that long.

 

[woodman88]

Just what size of building and what materials are you using that it will make such a cost issue wheither it is designed as a temporary building or not?

Garth Dreger PE
AZ Phoenix area

 

[3doorsdwn]

Just what size of building and what materials are you using that it will make such a cost issue wheither it is designed as a temporary building or not?

It's really too complicated a situation to lay out here (including the scheduling of everything). The temporary structure is a steel frame to be built.....(and yet another twist in this is I'm expected [to speed things up] to use an abandoned foundation that's off to the side).

It's got more twists than a pretzel......that's why I kept my original post as simple as possible so we didn't wind up discussing less critical parts.

 

[CptnBurns]

For info purposes only, I can tell you the British Standards, have a seasonal factor for sub-annual periods of 1,2,4 or 6 months.

For 4 month periods the site wind speed can be reduced by between 0 and 27%.

These obviously only apply to the UK, but going on that it would appear unlikely that you can get a "50%" reduction from your code, and if as you say your building it during storm season I would guess the reduction factor will be zero...