Wind Pressures on Horizontal Tubes
Wind Pressures on Horizontal Tubes
(OP)
Hi,
I am designing framing for a solar collector unit much like this one:
https://www.google.com/search?q=solar+chill+solar+...:
The framing is essentially four columns and four girders connecting the columns. The columns will need to be 7' tall in order to fit a generator underneath.
However, the unit is only slightly inclined, much closer to horizontal. The framing will not be attached to any other structure. From my understanding, in order to analyze the wind pressure acting on the tubes per Chapter 29 in ASCE 7-10, the tubes must be normal to the direction of the wind. This is not going to be the case. I am left to analyze the collector as if it were the "roof" of an open structure per Chapter 27, in order to size my frame members. Because of the generator underneath, I am assuming obstructed wind flow, thus increasing my uplift wind pressures. I feel that my wind analysis is too conservative if done this way.
Is there any other provision in the code which allows me to analyze the uplift pressures on the tubes similarly to that of lateral pressures on a chimney stack as in Chapter 29?
Thanks
I am designing framing for a solar collector unit much like this one:
https://www.google.com/search?q=solar+chill+solar+...:
The framing is essentially four columns and four girders connecting the columns. The columns will need to be 7' tall in order to fit a generator underneath.
However, the unit is only slightly inclined, much closer to horizontal. The framing will not be attached to any other structure. From my understanding, in order to analyze the wind pressure acting on the tubes per Chapter 29 in ASCE 7-10, the tubes must be normal to the direction of the wind. This is not going to be the case. I am left to analyze the collector as if it were the "roof" of an open structure per Chapter 27, in order to size my frame members. Because of the generator underneath, I am assuming obstructed wind flow, thus increasing my uplift wind pressures. I feel that my wind analysis is too conservative if done this way.
Is there any other provision in the code which allows me to analyze the uplift pressures on the tubes similarly to that of lateral pressures on a chimney stack as in Chapter 29?
Thanks






RE: Wind Pressures on Horizontal Tubes
RE: Wind Pressures on Horizontal Tubes
You misunderstood my question. Chapter 29 in the ASCE analyzes vertical cylindrical structures such as chimneys (they are perpendicular to the flow of wind). The solar collectors i am placing are going to be lying down horizontally, parallel to the plane of the ground. Therefore, I am not able to analyze the collectors as cylindrical elements per Chapter 29 with gaps in between and must instead analyze them as a "roof" structure per Chapter 27. I am not analyzing them in their most streamlined state. From my understanding, even though there is uplift due to wind on roofs, the "wind direction" is always defined as being parallel to the ground.
RE: Wind Pressures on Horizontal Tubes
RE: Wind Pressures on Horizontal Tubes
Fixed angle, or will you rotate them each month through the year to improve efficiency?
At that interval between the row of collector tubes, it is much more accurate to assume a complete single flat plate as the wind surface, not a series of individual tubes. reason is, the very small air gap between tubes stalls and blocks flow between the tubes, so it all acts as one big flat plate.
You indicate there will be four verticals, a side frame around the tubes, and a pump (or eqpt) below the array, right? So the exposed surface needs to be calculated like an inclined open roofed structure that height above ground. "Lift" occurs with winds trapped below at low angles to the ground (small latitudes) and push-over forces dominate at high angles to the ground (high latitudes).
RE: Wind Pressures on Horizontal Tubes
If I use Figure 29.5-2 in ASCE 7-10 for Open Signs and Lattice Frameworks, Note 2 says "The calculation of the design wind forces shall be based on the area of all exposed members and elements projected on a plane normal to the wind direction. Forces shall be assumed to act parallel to the wind direction." I interpret this as I can only use this figure if my sign or lattice framework is vertical as "wind direction" is lateral, but not necessarily the pressure derived from the wind. Do you agree with this interpretation? My solar collectors are sloped 20 degrees from the horizontal.
racookpe1978,
Latitude is 13.4443 degrees North. Not sure, but I think the angle of 20 degrees is fixed.
This is what I have been doing, using Figure 27.4-4. I am assuming it is an open monoslope building with a "roof" slope of 20 degrees. My client wants to use a certain structural tubing that he has already purchased, but it is failing in my analysis. I wanted to see if there is another less conservative way of doing the analysis before breaking the bad news.
RE: Wind Pressures on Horizontal Tubes