4 replies to this topic

[SkiBachelor]

Here is a picture that Bill took this summer at Summit Ski Area in Oregon.



After reading response in SAM about this today, I finally learned why the tower drum looks this way. The reason why the tower drum is lifted like this is not so mice can go in there and make cozy homes in the summer time, but it's designed for tower alignment.

[ccslider]

And isn't that a nice shot of the weld that is supposed to be visually inspected on a periodic basis due to the failure at Snowmass a few years back (early-mid 90's)? I recall having to shovel out each and every tower base on the Riblet towers to get a good look at the weld after that incicent.

[Kelly]

Embedment style towers (YAN common design) are set in a hole and adjusted by a level and transit sighted for the center line. Usually 3 winches (similar to a boat winch) with long cables are used for this adjustment as the tower hole is being poured full of concrete.

In the picture of the base (Riblet common design) the hole is around 8' deep. It's interesting to know that the embedded portion of this tower is commonly "guyed-off" by 3 winches as it is adjusted to the center line. Also an extension cord with a big stick can be used if no winches are available. This tower hole design uses less concrete and more of the earth under the tower to counteract the tower forces than a vertical embedment design.

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•  YAN_Riblet_base_red_2.jpg (45.36K)
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[Kelly]

Construction winch and cable

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•  Winch_and_cable.jpg (37.51K)
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[liftmech]

We have about three dozen of those 'jet winches' left over from various lift construction projects. An interesting note about embedded towers- Copper's lift guys were so well-versed in that type of tower footing after eight Yans that they got Poma to let them build the Eagle and the Flyer that way. Those are the only Poma detachables I've seen without a bolt cage footing. (K, L, and A-1- fixed-grip Poma triples- are also built that way.)
We should note that although Riblet's bolt drum is designed for tower alignment, it is the initial construction they had in mind. The sheaves are still aligned in the standard fashion up on the cap.