Wind Load Analysis

[chriskrol]

I am doing wind analysis on a building that is 600 ft long 180 ft wide and 50 ft high with 100 ft high tower at the end of it. There is an expansion joint right where the tower starts to separate the lower part of the building from the tower.
I was wondering if it is OK to analyze the 50ft high part of a building as low rise building and use Figure 6-10 (ASCE 7-02) to determine External Pressure Coeff. Cpf and then use Figure 6-6 to determine External Pressure Coeff. Cp for the tower or should I use Figure 6-6 to determine External Pressure Coeff. Cp for both lower part of the building and the tower.
I think since these two are separated by the expansion joint they will act undependably but I am not sure if such an approach is allowed.
Thanks

 

[JAE]

I would analyze each as a separate building. I also would be a little careful around the juncture between the two in that higher wind vortexes/pressures could develop both on the tower walls and the roof of the low building near the EJ. Perhaps be a little more conservative in those areas. The building probably isn't large enough to justify a wind tunnel analysis.

 

[haynewp]

I wouldn't base the wind load on the building from the height of the separate tower. There will be some different effects as the wind moves around the tower and affects the roof of the adjacent building. But you can't quantify this unless a wind tunnel test is done.

You will need more expansion joints to break up the 600 feet also.

 

[haynewp]

(I didn't see JAE's response before I posted.)

 

[JAE]

...but again - great minds seem to think alike, eh?

 

[chichuck]

chriskrol,

I remember at an ASCE Wind Loads Seminar a few years ago that this question came up. One of the presenters, the late Dr. Dale Perry responded with the following: "... you should design the building for what the wind will see."

I bring this up because you mentioned the importance of the expansion joint, and that it makes the two tower behave independantly of the lower portion. From Dr. Perry's comment, I'd surmise that the joint and the independent behavior do not affect what "the wind sees". That said, the joint certainly does affect the (dynammic) response of each portion to the wind loads. I agre with JAE. However, I'm sorry that I cannot give any advice on how to handle the vorticies around the juncture between the low roof part and the tower. Although I have seen sketches of this effect (additional vorticies and turbulance)I don't have any quantitative solutions.

just my $.02 worth.


regards,

chichuck

 

[RareBugTX]

Geeeese, I like that "You should design the building for what the wind will see." A few months ago I designed a building in a Business District (zoning issue) and I posted a question regarding the ACTUAL wind load on the upper part of the building. the neighboring buildings will likely be forever on the lot line. Almost everybody understood that I was trying to underdesign the MWFRS, when what I was seeking was a more realistic (critical if possible wind load) would be applied on the building

I definitely agree that the structures at least should be designed for wind with actual "what the wind will see"

Regards