Everyone who has been playing with magnets, knows that two magnets can repel each other. Now suppose we put many such magnets in a row, such that they all repel one another.
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We make a hole in each of the magnets and string them on a rope, like beads on a necklace. Now we tighten the rope. The rope should be rather tough, made of steel or carbon nanotubes or some such thing, such that it can withstand enormous pull. In my understanding the forces of the individual segments all add up on a string, such that over large distances the net force becomes quite substantial, especially if the magnets virtually touch one another.
Steel has been used a lot in the building industry, because it can withstand enormous pull. It is not so good for the compressing forces. By using the magnets in this way it may be possible to take advantage of the better quality of steel or whatever material and thus design pillars based on tightened strings. In the case of long pillars gravity also has to be taken into account, so the magnets at the bottom should be larger. Pillars based on strings and magnets are rather flexible and elastic, so some additional anti-flexing binding of many such pillars would be needed. Also some shielding might be needed to prevent the magnets from flying all over the place, if the string would break.