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Step 3Joists, hand rail sub-assembly and suspenders
The 37 joists on a 2 ft spacing are 2x8x8 treated lumber (all the wood in the bridge is treated lumber), while the handrail assembly consists of a 2x4x4 upright with an 2x4 angled brace to the end of the joist. The spacing between the inside of the handrail upright is 5 ft - wide enough for a garden tractor or a golf cart (really, a people cart). Only every other joist has a hand rail assembly
The connection between the suspenders (3/16ths galvanized aircraft cable, 850 lb working load) and the joist is a problem. One end of the suspender must be adjustable to permit as built corrections to tension, and thereby the shape of the bridge. The ideal connection would be a eyebolt through the joist with a turnbuckle between the eyebolt and the suspender cable. The problem with that solution is expense - when you need 74 of everything, forged or even welded 8 in eyebolts are expensive, and so are the turnbuckles. Instead, I chose to drill 1 in holes through the joists approximately 2 in from the bottom and just outside the handrail upright. Through this hole I threaded 3/16ths bright proof coil chain with an 800 lb working load. I threaded a 3/16ths thimble through the end chain links, then the cable through the thimble and finally clamped the two ends of the cable with two 3/16ths galvanized clips. If I do another bridge, I might try another approach, but this worked okay, if a bit cumbersome to build and to adjust once the bridge is up.
The aircraft cable suspenders and the plated chain were cut to length with a friction cut-off saw. 74 pieces of chain, all the same length (16 links) and 74 lengths of cables, 4 of each length except only 2 for the middle suspender, (2 catenary cables, each of which with identical dimensions each way from the middle). The length of the suspenders was calculated in the spreadsheet to account for a 6 in arch in the bridge as well as sufficient cable for thimbles at both ends, the compression fitting on the top end and the two clips on the bottom end. The suspenders were installed to dimensions calculated in the spreadsheet from bottom side of the catenary cable to the top side of the joists.
The connection between the suspenders (3/16ths galvanized aircraft cable, 850 lb working load) and the joist is a problem. One end of the suspender must be adjustable to permit as built corrections to tension, and thereby the shape of the bridge. The ideal connection would be a eyebolt through the joist with a turnbuckle between the eyebolt and the suspender cable. The problem with that solution is expense - when you need 74 of everything, forged or even welded 8 in eyebolts are expensive, and so are the turnbuckles. Instead, I chose to drill 1 in holes through the joists approximately 2 in from the bottom and just outside the handrail upright. Through this hole I threaded 3/16ths bright proof coil chain with an 800 lb working load. I threaded a 3/16ths thimble through the end chain links, then the cable through the thimble and finally clamped the two ends of the cable with two 3/16ths galvanized clips. If I do another bridge, I might try another approach, but this worked okay, if a bit cumbersome to build and to adjust once the bridge is up.
The aircraft cable suspenders and the plated chain were cut to length with a friction cut-off saw. 74 pieces of chain, all the same length (16 links) and 74 lengths of cables, 4 of each length except only 2 for the middle suspender, (2 catenary cables, each of which with identical dimensions each way from the middle). The length of the suspenders was calculated in the spreadsheet to account for a 6 in arch in the bridge as well as sufficient cable for thimbles at both ends, the compression fitting on the top end and the two clips on the bottom end. The suspenders were installed to dimensions calculated in the spreadsheet from bottom side of the catenary cable to the top side of the joists.
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After-the-fact picture taking is not possible, but you might add a picture with a couple of arrows or lines drawn indicating how the forces and cables will go.