Hinge Bases and Fold Over Kits

Question:  What's the difference between a Hinge Base and a Fold Over Kit?

Answer:  Our simplest base design is called a Hinge Base, in the sense that it allows you to hinge the tower up on two of the three legs.  Oftentimes, the 'Hinge Base' is confused with the hand- or motor-operated Fold Over Kit.  With a Hinge Base, two or three people should be able to 'walk' tower models up to 56' with light antenna arrays from their horizontal to vertical positions.  The Hinge clevis design which allows this to happen also is a convenient structural shape connecting the tower leg stubs to the threaded anchor bolts.  So this base is functional and cost-effective at the same time, if the owner does not expect to regularly want to get to and adjust the antenna.  If this is the case, we recommend our Fold Over Kits.

There probably are a couple less expensive designs to manufacture, but they would only be a few dollars less (any decent base design will cost almost as much as a tower section).  Furthermore, they would not have that helpful hinge feature, which makes installation easier  and usually less expensive, as well. 

Question:  I would like to avoid having to dig my hole any deeper than necessary.  Instead of digging my base hole about 3.5 ft. wide by 7.6 ft. deep (example), can  I just dig a 5' x 5' hole, since it's about the same volume of concrete?

Answer:  No, sorry, not really.  Yes, it may be about the same volume of concrete, but volume or weight in the base is not the key factor.  The key factor in the stability of the base is the amount of bearing resistance the base structure has in the ground in which it is planted.  Giving depth to a base is like adding a extension lever to a fulcrum: it gives it mechanical advantage/potential momentum in resisting the forces trying to move or tip the base and tower over.  As one insightful engineer put it, 'If you had a superstrong, lightweight substance, like styrofoam, that would not corrode or break, you could use this as a substitute for concrete and the tower base would be almost the same size as a concrete one.'  The deadweight of concrete only contributes about 5 -10% of the resisting moment in many typical tower bases; the rest is from the resisting force in the bearing surface of the hole.'  This also explains why soil types are important in determining the size of the concrete pad.  Most people own property with sandy or clayey soils.  Clayey soils are a little softer than sandy soils, e.g. a soil classified as some variation of 'clayey' would be considered to have a soil pressure of 100 lbs/cubic or sq. ft., while sandy soil combinations would usually have about 150 lbs./cu.ft. rating.  Our bases are typically designed for 'sandy' soild types or sub-types--to be installed in clayey soil types would require us to usually increase the depth requirment by about 10-15%.   If you or your building department are concerned about the exact soil type you have, you should get a professional soil bore sample.  (Sorry, we can not offer references in your area).   If you are fortunate enough to live on bedrock or shale or very hard soil, then a tower base at your site may only need to be 3 or 4 ft. deep and narrow enough to fit your base legs and rebar within it's diameter.

An example of this which shows the importance of depth versus volume of concrete may be shown by looking at the base requirements of one of our very strong 80 ft. towers (the 25 sq. ft. model at the 80 mph rating).  In sandy soil rated at 150 pcf, this base would need to be 10 ft. 7 inches, if the hole were drilled or excavated at 48 inch in diameter (circluar shape, with no less than 1/4" movement allowed at surface).  If the base-hole's width is significantly increased to 84" diameter, then a depth of 9' 0" would still be required to resist the tower's maximum overturning moment.  So a hole width increase of 36" only reduces the depth requirement by about half of that, specifically 19".  This 2:1 ratio is typical if applied to most of our tower configurations.