Ice loads on wind covered structures

[jdiggs]

Hope somebody can help me with another issue the code fails to clarify. At least it isn't clear to me.

In section 10.7 of ASCE 7-05 (wind on ice-covered structures) 1. states Vc shall be determined from figures 10-2 - 10-6 which are wind maps. These wind loads avg 30, 40, 50 mph.
7. states qz shall be determined using Vc according to 6.5.10 (basic qz formula)

My question is this:
Does the 10 psf minimum apply here. Using a Vc from the wind maps in 10-2 gives qz loads lower than 10 psf.

Thanks for your help

 

[jdiggs]

Ahhh, dyslexia is mother...Sorry

That would be wind loads on ice covered structures

 

[MiketheEngineer]

Just because it has a 1/4'' of ice on it - I would still think the appropriate wind loads should be considered including the 10 psf minimium....plus weight of ice...

 

[paddingtongreen]

Figures 10-2 - 10-6 show Ice Thickness and the Accompanying Wind Velocity for the geographic area; they give you both factors.

Out of interest, what "ice-sensitive structure" are you designing.

Timing has a lot to do with the outcome of a rain dance.

 

[jdiggs]

Foundations and supporting members for netting structures, such as driving ranges, baseball fields, etc.

Paddington, you are saying to use the Vc given in fig 10-2 (which gives you lower than a 10psf load) and the min does not apply?

Mike, you think the 10 psf min applies?

IMO, I think you may use less than a 10 psf load. My thinking is this:

The code tells you to use the Vc from the map in 10-2, it states that explicitly in 10.7 #1

The reason I don't think the min applies is because all these values give numbers below 10 psf

Thanks for the input

 

[akastud]

I design a lot of power lines in ice regions. In doing so we end up often using another code from the National Electrical Safety Council. In that code you put 9 PSF on your ice and another load case with full wind loads. I would feel comfortable putting less than 10 on the structure and I agree with jdiggs.

akastud

 

[JoshPlumSE]

I'm curious what type of structure this is.... I do a lot of communication towers and their code has relatively detailed provisions for how to address wind + ice loading.

 

[paddingtongreen]

"Paddington, you are saying to use the Vc given in fig 10-2 (which gives you lower than a 10psf load) and the min does not apply?"

Yes, you do your regular design using all of the regular loads including wind, then, as a special case, use the lower wind load on the larger width, heavier, ice coated structural members.

--------------
akastud, we once used 4psf wind per NESF on transmission lines. I think you use more ice than we did too. Climate change?

Timing has a lot to do with the outcome of a rain dance.

 

[jdiggs]

These are all Importance cat 1 structures. Baseball backstop poles, Driving range poles, landfill nets, etc.

That's one of the other reasons I would be ok with dropping the load less than 10 psf. Life safety is usually not an issue (when ice on wind applies), the owner does not want to pay to design these things for 70% solid, and usually the net fails at the connections and falls due to the additional weight of the ice.

 

[paddingtongreen]

Are you using the lowest possible shape factor?

What it finally comes down to;
1. Can you live with the risk? will your insurance cover you in the event of failure? the owner may turn around and sue you for doing a lousy job if something happens. It has happened before, an owner pushes, verbally, for a cheap and nasty job, and then sues when one of the chickens comes home to roost.

2. If you go along, can you get it past the Building Official for permits?

Timing has a lot to do with the outcome of a rain dance.

 

[jdiggs]

All I want is a code clarification so I can follow code.