How to determine the overturning moment on a stand alone, uncovered bean pole tipi I will preface this by saying I am a highschool student who has not yet had a physics class. I engineered and built a hexagonal shaped, open bottomed, planter to hold soil that would contain pole beans that would climb the conduit poles set in the planter. This was to be a feature in a children's garden that will also be utilized by the handicapped in our community. I submitted plans and was approved with the caveat that the structure rest on top of the soil and not be tied down as part of it covers a septic field. Now that I have completed the structure and am at the point of passing inspection, the city has decided that the planter should be fixed to the ground, while the county still insists that it shouldn't. I am therefore trying to accumulate the mathematical evidence to prove that this structure will withstand typical wind forces and be safe, otherwise I have a rather expensive paperweight on my hands. 
The pertinent information I have calculated is:
Approximate weight of the planter: the outside lengths of the planter are 90 inches, while the interior are 72 inches, it should also be explained, that although hexagonal, the planter has five sides with the sixth left open as a doorway. The width is 14 inches between the horizontal planes and 18 at the diagonal connections. The planter is 12 inches high. Using these numbers I calculate that the planter will hold 7.875 cubic feet of soil. Online I have noted that the engineering constant for soil with "typical" moisture content is between 100-120 pounds/cubic foot. Thus without the weight of the boards, the soil alone will weigh anywhere from 3,937.5-4,725 lbs. depending on your numbers. The poles are 3/4 inch rigid steel conduit at 15 ft lengths. Each pole is approximately 15 pounds. There are six poles which adds another 90lbs to the overall mass of the structure. 
Wind load of poles: 
Using a generic formula of Force= (Area)(wind pressure)(drag coefficient)
I calculated that a 15 ft pole that is .75 in. wide has has an area of 135 in. per pole, times 6 poles, is equal to 810 in. or 5.625 square ft of surface area. I took a constant of a 70mph wind (12.5psf) since that would be an outlier for this area, and the constant of 1.2 as the drag coefficient of a long cylinder. 
Thus: (5.625 ft squared)(12.5psf)(1.2)=84.375 pounds of wind load pressure
This number bothers me however in that it assumes that the poles are in a perpendicular plane instead of the 55 degree angle that they are at. The calculation also does not take into consideration that the base is 7.5 feet in between poles. 
How do I calculate how high a wind this structure can take before toppling over? 
I deeply appreciate any help you can give as I am defiantly out of my league, but am eager to learn

 A: Sorry but I think this question is "off topic" : it is about civil engineering, and asks how to calculate something; it does not ask for an explanation of a specific physics concept.  See the site policy at https://physics.stackexchange.com/help/on-topic.
It is quite difficult to predict the effect of the wind on such a diverse structure - you need to calculate the forces on each element from various angles, and their effect on the whole structure. A computer program might be needed. 
Easier and more reliable is to test your structure when loaded as in use - if you can find suitable wind conditions. If you cannot find a windy place (and even if you can), you should test it against improper use by pulling on various corners to see if you can make it topple or fall apart.  If it does  topple, investigate ways to weigh it down. You might also want to think about strengthening the framework by adding cross-beams.
Since the goal is to satisfy safety regulations, have you asked for advice about doing this?  eg What kind of proof will be needed?  A calculation of your own is unlikely to persuade the authorities, it would have to be certified by a civil engineer (I expect).  Even if you test your tipi in high winds, you will need some kind of proof that it has passed the test, perhaps again from a civil engineer. 
You could try posting your question on Engineering SE, where you are likely to get better advice.   
