Saturday, July 14, 2018

(60) Golden Reef Mine Tramway Chapter 2 Tower Design


GOLDEN REEF MINE TRAMWAY
Tramway Design
Chapter 2 of 5


The design of the system is the second subject on the Golden Reef Mine Tramway project. The first chapter gave us the discovery and early history. The design of the tramway was developed by using good engineering practices, approved and stamped by a Certified Arizona Structural Engineer. The major engineering focus was to ensure adequate footings to anchor the towers, proper tower material specifications, tower structure tension loading and cable anchor component limits.






We had to come up with an overall design for the tramway. The major concern was that the towers would hold the tram buckets and would not fall over or fall down. The stationary cable anchor was a concern as well as the foundation. Most of the engineering was associated with those two areas. The towers would be fenced in and no access would be allowed by the general public when the system was operating. The arrangement would include towers that will be strong enough to support the 250 tram buckets plus 50 feet of (7/8” wire rope (1.5 lb/ft X 50 feet = 75 pounds) for 375 pounds on each 1 1/8” cable. One of our volunteers is an engineer, but his Arizona registration in nuclear has expired. He assisted in doing the design work. We later hired an Arizona Licensed Structural Engineer to review and stamp the design.

Tower Basic Design We decided to duplicate the towers that are on the mountain and they should support the weight of the cables and buckets. The towers on the mountain were all made the same dimensions for the basic tower. The picture below shows the numbering system we used to identify each piece of wood. There were (13) pieces of wood in each basic tower.
Use of Cribbing The object at the Golden Reef Tramway was to keep the towers about the same elevation on the crest of the mountain. The towers that were over these dips were cribbed up to keep the cables level areas that dipped down where they constructed cribbing, pieces #8 & #9, on the above picture. We did not have to use these timbers in our application. See the picture below.





Original Tram Station There was only the upper tram station that was still standing, but was not complete. This tramway was probably a gravity run system, since we could find not evidence of any drive mechanism. They would have relied on the weight of the full buckets to move the ore from the mine down to the stamp mill and move the empty buckets up to the loading tram station. The picture below shows what was left of the station at the mine. The ore bin has been partially disassembled, the transfer area was also partially disassembled and the horizontal pulley was semi in place.




TRAMWAY NEW DESIGN

Tower Materials Specifications The table below shows the original timber sizes on the tram towers. The numbers in parenthesis are the dimensions of the timbers that the two towers were constructed. The larger dimensions added to the original design and strength of the tower structure. 
 


Tram Tower Foundations Each tram tower weighs approximately 1,500 pounds plus 2,440 pounds of tram cable/bucket tension for a total weight of 3,940 pounds of vertical force on the concrete footings are 24” X 24” X 36” with rebar to stiffen each of the footings. The towers are anchored with 5/8” steel plates and 1” all thread anchors to prevent the towers from overturning. The drawing below shows the configuration of the concrete supports and anchors for a tram tower:
 

New Tower Configuration We used a basic layout of the original tramway using two tram towers with stationary cables anchored on both ends of the towers. There will be a moving “continuous” cable with a small motor to run the tram buckets which are supported on the stationary cables. The drawing below shows the basic tramway layout and the location of the major components on the towers:  



Tension on 1 1/8” Cable The tension on the 1 1/8” cable is based on cable weight per foot, the tower span, 18” droop, the bucket weight, and the small cable support



Tower Loading Design The tower loading design is based on the 1 1/8” cable tension, height of the towers, angle of the anchor legs, weight and leverage of the footings and the weight and leverage of the towers. An acceptable safety factor against overturning the towers has to be greater than 1.5. Our safety factor is about 13.1.



Tower Anchor Components The tower stationary cables are anchored to the ground via a swage attached to the cable through a shackle to the head on the ground anchor for the north tower and the south tower has that same arrangement with a turnbuckle to allow for adjusting the droop on the cable. All of the components were over 10,000 rating. Our system was 4,400 pounds with a 100% safety factor of 8,800 pounds. This is well below the rating on any of the connectors on the 1 1/8” cable system.




 1 1/8” Cable specifications

Calculated Tension on Cable 4,400 pounds times Safety Factor = 8800 pounds

Cable Swages (1 1/8”)                                   ≤ 34,000 pounds

Cable Turnbuckles (1 ½”)                               ≤ 21,400 pounds

Cable Anchors (3/4”)                                      ≤ 26,500 pounds

Shackles          (1”)                                         ≤ 20,000 pounds

Cable strength                                                 ≈ 34,000 pounds



7/8” Continuous Cable The continuous cable will be the driver for the tram buckets. It will be connected to itself via a double ended swage. The tension on the cable will be enough to ensure the horizontal pulley will adequately grip the cable. The tension will be maintained via (4) 1” all thread rods that will make the adjustments.



7/8” Cable specifications

Weight on Cable 313 pounds times Safety Factor = 626 pounds

Cable Swages                                                 ≤ 21,400 pounds

Cable strength                                                 ≈21,400 pounds



Tension on 7/8” Cable The tension will be based on having an 18” sag in the cable, a 250-pound tram bucket riding on the large cable, and the smaller 7/8” cable weighing 1.5 pounds per foot over a 50’ distance. The horizontal tension will be about 313 with a safety factor of 626. This tension will not be a significant factor since the cable and swages are good for 21,400 pounds. The picture below shows the continuous cable in red.


Driver End Mechanism The north tower will have the driver mechanism that will move the tram buckets. This will be constructed similar to the way it was done back in the day at the Mayflower Mill in Colorado with a horizontal pulley. The drawing below shows what the station will look like. The horizontal pulley will be driven by a 1 Hp motor reduced from 1759 to 62 RPM that will move the tram bucket the 50’ in about a minute. 


Driven End Mechanism The south tower will have the tension adjustment that will keep the cable tight on the horizontal pulley and ensures the system will function properly. The construction of this end is not similar to the Mayflower Mill in Colorado since they incorporated a very large weight to maintain the tension. We use the all thread to maintain the correct tension, since we are only dealing with only two towers and a 50-foot distance between the towers. The drawing below shows what the station will look like. The horizontal pulley adjustment will be made using the (4) 1” by 36” all thread that will maintain the tension on the system. This is a fairly simple mechanism that should work well.








This concludes the engineering design of the Golden Reef Tramway for the Cave Creek Museum.



 NEXT: Chapter #3 Tram Tower Construction



















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