Wind Loads on a Barrel Vaulted Walkway Canopy

[jdelacruz]

Does anyone know a good procedure using ASCE 7-05 to follow on determining wind loads on a barrel vaulted walkway canopy? The canopy is a main entrance canopy approximately 85 feet long and about 20 feet wide in its cross section. The apex of the curved is about 4' from flat. The total approx. height from the ground is about 22'. I just need design procedure using the formulas (i.e. not having to resort to wind testing) on a free standing barrel vaulted canopy detached from the main building. I realize that ASCE 7-05 does have provisions in figures 6-18a to 6-18d on free roofs but it seems not to cover barrel vaulted structures. Thanks.

 

[civilperson]

Use Figure 6-8 of ASCE 7 for arched roofs.

 

[jdelacruz]

Do I need to use the 'free roof' provisions of ASCE 7-05?

 

[JLNJ]

I think the British code might have the exact case (open, barrel vault) you are looking for. ASCE 7 is very limited when you are looking at large overhangs or canopies.

 

[jdelacruz]

What is load case A and B referring to in the free roofs figure in 6-18? How would one apply these load cases with load combinations?

 

[theonlynamenottaken]

Case A and Case B, and Clear & Obstructed Wind Flow essentially create different Windward/Leeward configurations of the most "inward" pressure situation and the most "outward" pressure situation. Furthermore, "Obstructed Wind Flow" creates more "outward" pressure.

The short answer of how to incorporate wind on open structures into load combinations is to use each wind case ( in each load combination including wind... which effectively multiplies the number of total load combinations by ~3.

After a few projects with open structures you can identify by inspection the worst case "inward" wind pressure case and the worst case "outward" pressure case for the element your are designing/analyzing for. Then include the most "inward" pressure wind case to the "downforce" critical load combinations (those combinations using D (ASD) or 1.2D (Strength)) then use the most "outward" pressure wind case with the "uplift/overturning" critical load combinations (those combinations using .6D (ASD) or .9D (Strength).

 

[mudflaps]

Don't forget about a significant uplift at the columns. Probably going to need a pile or lots of concrete for "dead load". Think of this thing as a big airplane wing just waiting to take off.

old CA SE