Safety factor for administrative hypothesis 1

[cesaramorim]

I've received a pole des project where the client requires the following:

For administrative hypothesis:
A safety factor of 1.8
Wind pressure on the face of the pole: 840 Pa

For extreme wind:
A safety factor of 1.1
Wind pressure on the face of the pole 2050 Pa

My question is, what exactly is it refering to?

Is extreme wind a reference to Ultimate limit states? Or accidental winds?

Is administrative hypotesis refering to Serviceable limit states?

 

[kingnero]

What did he say when you asked him these questions?

http://www.fusionpoint.be

http://be.linkedin.com/in/fusionpoint

 

[ChadV]

I think you need to clarify with your client to be certain - the guesses of we folks on the internet certainly aren't anything to hang your hat on.

With that being said, it sounds like maybe there is a language translation issue here - I could see the "service" in "service loads" being translated as "administrative".

 

[cesaramorim]

I was expecting someone with access to ASCE 48-05, or with some sort of previous experience could provide a clear answer

 

[Lomarandil]

I also suspect "administrative hypothesis" is a mis-translation of "service condition"? -- Cesar, can you confirm or post the original language wording?

It's been a little while since I worked with ASCE 48, but I don't think the factors of safety mentioned refer to ULS or SLS specifically. Just that they want your structure to resist a "common" wind load with an F.S. of 1.8, and an "extreme" wind load with a F.S. of 1.1.

Never heard of accidental wind.

But all that said -- pick up the phone and ask the client.

 

[cesaramorim]

As far as I remember any load can be considered accidental, since the EC1 establishes an accidental load if needed that might be considered in different sittuations (fire, snow, etc). Only accidental seismic loads are specific to eartquakes.

The client is Indian, so the language is probably Hindi, and I can't contact him so far.
Edit: I received the data in english language

Anyways thanks for all your help

 

[rb1957]

I think this is a translation issue ... I read it as they are specifying a smaller safety factor for a more extreme wind loading ... not unusual. Looking at it the more severe windspeed is the critical design case.

another day in paradise, or is paradise one day closer ?

 

[cesaramorim]

The problem is that most of the loads are from the cables weight and not the wind. So when I use a factor of 1.8, the "administrative hypothesis", or serviceable limit state, deals more burden to the pole than when I use the 1.1 factor. The wind pressure is worse in the extreme winds, but it only afects the pole, and not the cable loads.

A SLS that is more burdensome than ULS makes no sense in my opinion. I'll try to contact the client and provide feedback if possible.

 

[rb1957]

it makes sense to me to have a lower factor for a more sever loadcase. if other loads make the lower windspeed case critical, then so be it. but it is always worth touching base with the client.

another day in paradise, or is paradise one day closer ?

 

[jayrod12]

I've had many a job where the SLS criteria governs. 30ft beam spans are the most common culprit.

 

[IDS]

A SLS that is more burdensome than ULS makes no sense in my opinion. I'll try to contact the client and provide feedback if possible.

If you are designing for strength under both load combinations, then they are both ULS.

To have a frequent ULS with a high load factor being the critical condition, rather than a rarer ULS with a lower load factor, is not at all unusual.

Indeed it is a desirable outcome, where achievable.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[racookpe1978]

No. For wind loading, the wind load (on the main pole) from the 4x guy ropes - compared to the single main pole's wind load - may well be comparable. 4x cables times a smaller cross section than the vertical main mast, but each guy rope has a longer length.Add to that the weight of the 4x guy ropes, PLUS the fact that the tension in the sideways angled guy ropes increases the sideways force on the mainpole if any one of the guy ropes breaks or loosens.
Also, the largest wind load will occur when the winds "sees" all 4x guy ropes. There will never be a reasonable case when the central vertical mast "hides" the downstream guy ropes.

 

[hokie66]

racookpe,
I don't think he is talking about a guyed pole...didn't mention guys.