Mill Creek Central Trestle Tower Construction I
A construction company would build the trestle by first doing all the foundations, then erect the towers, than install the beams, etc. The folks who volunteer at MCC are multitalented but none are structural engineers and none of us have undertaken a similar project. We decided to erect one tower first to make sure we liked the design and that we were actually able to erect it.
We decided to start with the third tower from the north end which is about 20.3 feet tall. (We initially though that tower 3 would be the tallest. However, after the foundation for tower 4 was poured we found that it will be about 6 inches taller then number 3.) Tower 3 is in the flat part of the valley (we later recognized how nice this was when working on the foundations of the towers on the steep north slope). We figured that if we could erect #3 , the rest would be easy (or at least easier).
The first thought was to build the tower in place. However, a trial of stacking panels just two high proved difficult. So, we build the tower on the ground and figured we could rig something to stand it up.
Dan Staron and Dick McCloy decided that they could use the backhoe to stand the tower up. Photo at right shows Dick on the backhoe and Dan directing him. The photographer had less confidence and was well out of the way --- telephoto lenses are great!
This was a significant milestone --- we had confidence that we could get the tallest tower up with the tools on hand.
This is the top of tower #3. The two 4 inch channels closest to the camera are the caps on which the beams will rest. Below the channels is a pair of short panels only 6 inches high with the bracing oriented horizontally. Next is a pair of 5 foot high panels orientated with the bracing vertical. Further down, the next pair of 5 foot panels has the bracing horizontal, then a pair with the bracing vertical. The bottom 5 feet of the tower is best seen in the next photo.
The bottom 5 foot panel was the correct length but had bracing only horizontally. The ends of the panel had 1 inch long stubs of 2.62 inch OD tubes that were intended to fit into the next panel. The lower 6 inches was cut off both panels and the pieces reattached with the braces orientated vertically and with the stubs inside the tubes at the joints. Note that both ends of the tower have short pieces of panel with the bracing running 90 degrees to the adjacent panels. This orientation assures that the towers are stable squares.
The foundation for tower number 3 was being constructed at the same time the tower was being finished and painted. The photo above shows the foundation for the 4 leg core which was made first.
This is the entire 8 leg foundation with the base channels in place ready for the tower to be set in place.
The photo above shows Dick moving the core tower from the assembly area to the tower site.
The photo above shows Jim Norris (partially hidden) and Dan Staron positioning a timber between the tower bottom and the backhoe prior to standing the tower up.
Photo at right shows the tower going up.
The next step was to move the tower over the base as shown on the left. The backhoe was able to hold the tower erect with some slack in the chains which enabled us to position the tower over the base and then lower it the last inch or so. We then adjusted the base channels so that the tower was exactly vertical. Once everything was correct the tower legs were welded to the base channels.
That is Dan Staron on the right checking out the tower stability. It was stable.
The next step was to move the side legs into position against the 4 leg core. This photo shows Dick moving a side to the tower location.
This process didn't work as well as we liked. Next time we'll probably use a hoist of sorts to lift the top of the side legs into position.
This is the finished tower number 3. Note that horizontal braces have been added between the side legs and the center square.
We were satisfied with this tower. At this point we had confidence in the process and are now proceeding with the remaining tower foundations and towers.