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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