Pier and a Deck
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If the observatory is to be placed on, for example, a five foot high deck, you might well have a separate pier down through a hole in the deck. The pier might be a steel pipe, column of concrete, or it might be built up using concrete block as described above.

However, suppose for some reason you cannot build a pier down to the ground and you need to have the pier supported by the deck itself. You would probably design the deck support structure to be as open as possible so that wind forces would have relatively little effect. In addition, you might deliberately design the deck so that its sideways movements result in translation, rather than rotation of the floor. For example, if the deck is supported on parallel vertical posts, you could install deck fastenings that are designed to flex. As shown in Figure 6.5, pressure of the wind will then tend to bend the deck supports, but the deck will tend to move sideways, rather than tilt. Thus, within limits, "loose" or flexible fastenings may be superior to "tight" fastenings!

Figure 6.5 MAGIC DECK OR PIER

In theory, one could build the pier itself of four relatively small pipes with a pier head designed to stay level in the presence of sideways pier forces. Such a design would require great care, because changes in the center of gravity of the scope as the scope follows the stars might introduce tracking errors if the pier head flexes. Keep in mind that this approach is not generally preferable to a more conventional rigid, massive pier and footing. However, if circumstances prevent a conventional pier design, this type of approach may lead to a pier design that satisfies your needs.

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