Wind on Ice - ASCE7-16

[penpe]

I'm finding that wind on ice has a significant effect on lateral loading of our elevated cable trays, as the projected area is increased by 25%. A previous thread on this subject opined that it's overly conservative to assume worst case ice and worst case wind happening simultaneously. I tend to agree, but can't find in ASCE7 any provision for reducing wind load during occurrence of max ice thickness (which is to be added to all free edges of the projected area). In section 10.8 design procedure step 1 directs to maps for nominal ice thickness and concurrent wind speed (labeled "gust speed" on the map). But step 10 directs to determining design wind force in accordance with Chapter 29 - which leads back to worst case wind speed.

Am I missing some exception that would reduce wind force on ice?

 

[flight7]

ASCE 7-16 section 10.5 says that the wind speed shown on the Chapter 10 maps is the speed that is concurrent with ice. You can use that relatively low speed with the procedures in Chapters 26-31 to determine the wind load on ice-covered structures. You don't need to pull the higher speeds from the Chapter 26 maps.

 

[penpe]

Thanks for the reply. The use of the word "gust" on the Chapter 10 maps is confusing, because section 26.11 addresses "gust effect factor" separately. But their saying "concurrent with ice loads" does provide a convincing argument. Are you saying that wind force on iced elements would be calculated the same way as in Chapter 26, by substituting gust value from Chapter 10 maps for the "basic wind speed" value used in determining velocity pressure in equation 26.10-1? That would result in a much lower force, insignificant for my location compared to typical basic wind speed.

 

[structSU10]

That is correct. I did exactly as flight says on a recent project, using the wind speed from chapter 10 to compute wind pressures.

 

[penpe]

Thanks very much!