wind loads for hvac screen walls at grade

huangyhg

wind loads for hvac screen walls at grade
i have a 4-sided solid screen-wall enclosure 12' tall x 24' wide x 45' long around an hvac unit located at ground level. the top is open. the adjacent walls provide some bracing near the corners. however, most of the wall panels are braced by cantilevered steel columns. the column spacing is 8'+/-.
what asce 7-05 wind loads should i use?
parapet loads 6.5.12.2.4?? not on a roof
solid freestanding walls 6.5.14?? 4-sided, i need to design the corner columns and corner bracing
rooftop structures and equipment for buildings 6.5.15.1?? not on a roof
solid freestanding walls and solid signs
i second that.  definitely solid freestanding walls.
for a twist to the original question, if the 4-sided screen wall is on a roof, is the answer the same?
well, that confuses things a little for sure.
first, the height will come into play.  so basically you have solid wall at ground, but ground is whatever elevation the roof is at, rather than sign above ground.
second, the new asce7-05 requires a 1.9 multiplier for roof top structures and equipment.  this is given in section 6.5.15 and 6.5.15.1; however, 6.5.15 does not include the provisions for solid walls (figure 6-20), but does include chimneys, tanks, and roof top equipment (figure 6-21).  so do your solid walls act like a roof top structure, such as a square tank, or like solid freestanding walls?  this is one i can not answer, as we have discussed it in house and not reached a consensus.  the confusion arises since the solid walls section is omitted from 6.5.15.  
of course, you are not allowed to use teh screen walls to reduce the wind pressure on the actual equipment, so the equipment would still need to be designed using the pressure from 6.5.15.1, with a factor of up to 1.9 over the wind pressure from figure 6-21.
it is my personal opinion that section 6.5.15 should also include figure 6-20 for calculating cf.  so that is what i do, as i think that screen walls would see a similar increased pressure as a large, solid piece of equipment or doghouse.