Upper tier bridge (part 3)

The support piers on the other side of the bridge follow the same principle as described in the last post, but were easier to build because the bridge is only one-track wide at this point and the necessary joists are already in place. This photo shows the piers in place with C-clamps, a beam resting on top, and two levels used to verify that this end of the bridge is level with the other end.

It turns out that drill access to those piers was also problematic, and in fact I had to trim the leftmost pier to work around the middle tier subroadbed. I again used wood glue to hold the piers in place, this time snug against the adjacent piers, until the glue dried and I could put in the screws without C-clamps in the way.

In the next photo a quite a bit more has happened, and the bridge is starting to take shape:


In this photo the bridge beam on the right side is in place and the bridge itself has been positioned. Screws (#4, 1/2") have been added to the bridge floor to affix it to the beams. The end of the bridge on the right side has been trimmed to where the 1/2" plywood subroadbed will meet the lauan plywood, and the beam has had a notch cut in for where it will be supporting the 1/2" plywood.

In addition, the bridge "walls" have been attached to the edges of the bridge floor. These walls are 1 1/2" tall -- which is enough to add the lateral strength needed. They are attached with #4 1/2" screws, as was done with the middle tier bridge.

Unfortunately, the leftmost bolt is too close to the edge to allow a washer to be placed on it, now that the wall is in place. Minor oops -- I'll just trim some of the wall to make room.

One change not quite as visible is that the subroadbed for the upper tier entry track (adjacent to the back wall) is in place. I put this in when the bridge was removed. I was holding off on this task only because I wanted to verify that the subroadbed would not be in the way of the bridge.

In this next photo the bridge is ready for track:


The obvious changes from the last photo are that the blue roadbed is in place and the track path has been drawn with a marker -- the 30" radius curve I discussed in the first Upper Bridge post is the path used. Some changes from the previous photo are:

1. The roadbed and track have been laid for the upper tier entry track in the back. I did this now because it will be harder to access that area after the bridge is in place. You may also note that feeder wires are attached. If you look very closely you may also detect the upper tier auto reverse (AR) bus in yellow and blue, which has now been routed along the back of staging, where unfortunately it won't be very accessible after all three tiers are in place. I really hope I never need to get to this later. I did make sure that the places where the feeder wires attach to the bus are accessible.


2. The bridge has been leveled in all directions at all points. Interestingly, when the leveling was done at the nut/bolt/washer support piers I found that the pier tops were not level with each other, although I thought I'd leveled them by eye. It doesn't affect anything, except to show that leveling by eye doesn't cut it.


3. The last few inches on either side of the bridge have been separated from the main bridge by manual saw. These end sections will be permanently affixed to the support beams underneath, while the main bridge will be removable. The reason for doing this was to assure a very level transition from the bridge floor to these end sections.


4. Because the bridge is meant to be removed occasionally, not frequently, the bridge is attached with screws on the beams and of course the nuts on the middle piers. In order to access the screws the blue roadbed has had holes cut where the screws are.

The next post will cover the track placement (and will end the topic of this bridge). My intent is to use sectional track with railjoiners on each side. This will make the operation of replacing the bridge a little more challenging, but should greatly decrease the chance of derailments. Of course, if that approach doesn't work out I can remove and replace the track without changing the rest of the bridge.