In my opinion, the only reason to use wind tunnel model testing is to validate a design that would not otherwise meet the analytical criteria.  This would most likely be driven by a significant cost savings in using the design as compared to perhaps a more restrictive analytical design.

Ron, could you please give an example...this subject is very interesting and I'm willing to know more as well
Thanks Ron

We have a 48 story building going up in our city and the structural engineer of record told me that they did a wind tunnel study for it.  Surprisingly, the wind forces came up higher than the code requirement.  Usually, this is not the case.

I used a wind tunnel study a few years ago on a domed stadium where the forces were quite a bit smaller.  Both of these projects used a firm up in Guelph, Ontario (spelling?)

Colorado State University also has a wind tunnel for this purpose also.  

For our stadium, going to a wind tunnel was based on the unique shape of the structure (it had stay-cables) as well as the desire to economize the design for such a large structure in a non-seismic zone.

It is possible that your tunnel study could produce lower wind forces that would make seismic loads a more important consideration.

We do wind tunnel testing from time to time on large bridges to develop a feel for the behavior of the bridge that would otherwise not come from the static cases usually found in the code.  One benefit is that loads are sometimes less, however the single greatest benefit is the overall behavior and correlation to advanced modelling techniques.  Once corroboration is achieved, computer models may be run on several different configuration knowing that the results should be within the ballpark.

Ontario seems to be popular for this work!

You have a nice description of Wind Tunnel Engineering to structural purposes in

Steel, Concrete and Composite Design of Tall Buildings
2nd ed
Bungale S. Taranath
Mc Graw Hill

Section 2.6

By the way one of the finest books as pertains to wind forces.

There it is stated that prismatic forces are candidate to such studies when the height exceeds 40 or 50 stories.

thank you.

I was at a talk by Bill LeMeasure one time, and to paraphrase what he said "It would only be prudent to do a wind tunnel test on all high rise buildings".

Remember the CitiCorp Building in NYC and the Hancock building in Boston.