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Deck Truss Bridge - May '04

Installed cross-bracing and ties

The bridge needs cross-bracing to prevent it from collapsing sideways. This is critical because a heavy train crossing the bridge (on curved track) will exert a large lateral force toward the outside of the curve. The structure is braced at seven equally-spaced points along its length, with each cross-brace consisting of a pair of 3"x4" horizontal beams plus a pair of diagonals. The beams are sandwiched between the truss stringers by 34" threaded rods; the diagonals are attached to the beams with carriage bolts. Seven braces is overkill - I could probably get away with just three - but I liked how the extra bracing adds "density" to the bridge's appearance.
Here's a closeup of a cross brace. Each horizontal beam is made of a sandwiched pair of 2x4's and has a half-inch-square channel running down its center to accomodate the threaded rod; the rod is bolted on the outside of each truss. The stacked blocks below the end of the bridge are to adjust side-to-side and end-to-end leveling.
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Here's a view of the bolts (on the ends of the threaded rods) that secure a horizontal beam. The diamond-shaped things are 3" square pieces of 1/4" thick steel that act as a large washers - standard washers, which are about 1" in diameter, would pull into the wood when the nuts are tightened.
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Here's the bridge with all bracing installed.
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And here's the other end of the bridge. The big pieces of wood on the ground under the end of the bridge are a pair or used RR ties bolted together (something I didn't think of doing on the other end); the tie nearest the camera will be the bottom layer of a header that will look just like the one at the other end of the bridge.
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Looking down the center of the bridge.
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I installed three crossties because I just couldn't wait to see how the finished deck will look. Each tie is anchored at each end by a 4" timber screw. The screws don't require washers but I added them for a more "industrial" appearance. Soon the length of the bridge will be covered with these 1.5" wide x 2" tall x 32" long ties spaced every 1.5", and eventually the rails will be fastened to each tie.
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All the crossties have all been cut and drilled, and are awaiting paint before being installed on the bridge. Each tie is roughly the size of a baseball bat.
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A closeup of a 4" timber screw with its industrial-looking washer.
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It's easier to paint the bridge's crossties before installing them, so I created a painting "tool" from a length of 3" diameter PVC pipe that I capped at one end. I filled the pipe with paint then dunked each tie down the tube, brushed off the excess paint, let it dry a bit, then dunked the other end. It turned out well, but 120 dunks is a lot of work!
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I created a tie-drying rack by driving a bunch of 2" finishing nails into the sides of a 2x4 that I then laid across a pair of sawhorses. I hung the ties on the nails using the ties' pre-drilled screw holes. It kinda looks like a giant black windchime!
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I created a tie-laying jig by nailing some small blocks to the underside of a piece of scrap plywood. The jig speeds up installation by automatically spacing and squaring the ties as they're fastened down.
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All ties are installed and the bridge is complete! I still need to build the bulkhead at the far end.
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The completed bridge from the other end, artistically framed by some trees.
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