Fig. 318. View of Part of the Bridge, with Letters Indicating the Various Frames.
A B frame was now hauled out to one of the towers and lifted by its narrower end, with fall and tackle, until its lower tie piece rested on the projecting ends of the center crosspieces of the tower. The upper end of the frame was held against the top of the tower, while a C frame was hooked over the upper ends of the tower legs; then frame B was allowed to swing outward until its smaller end locked with the outer end of frame C. It will be observed in Fig. 306 that the upper crosspiece or tie piece of frame B was fastened to one side of the vertical sticks and the lower tie piece to the other side. This was done purposely, so that when the frame was set in position the bottom tie piece would be on the lower side of the frame and the top piece would lie on the upper side, as shown in Fig 318, or, better still, in Fig. 319. The rest of the frames were all arranged to be set in place with their tie pieces on the lower side, or facing the towers, as will be clearly understood by examining the illustrations. As soon as the B and C frames were set up on one side of the tower, another pair of B and C frames was set up on the other side of the same tower. A cantilever bridge must always be built out on both sides of the tower at the same time, otherwise it will be overbalanced on one side and topple over. After the B and C frames were in place we took two D frames, with oppositely cut ends, and rested their tie sticks on the top of the tower, just under the ends of the C frames. The ends of the two D frames overlapped at the center of the tower, and, as one was cut away at the outer side and the other at the inner side, they fitted neatly together and were fastened with bolts. The D frames were supported near their outer ends with E frames, which rested on the B and C frames. Fig. 319 shows an E frame set in position on the landward side of the tower, while two of the boys are climbing out on the opposite B and C frames preparatory to setting up the other E frame. A cross stick was now bolted to each D frame, just beyond the upper ends of the E sticks. This done, the frame F was hooked in between the ends of B and C, at the shoreward side of the tower, and its outer ends were supported by frame G, which was hooked over frame D and the upper ends of frame E. The frame L was then rested on the ends of frame F and G, and supported the shore end of frame D. A stick nailed across frame D on each side of the upper ends of frame L served to hold the latter in place.
Binding and Anchoring the Structure.
Fig. 319. Preparing to Put an E Frame in Place.
As the different frames were coupled together, we bound the overlapping ends with soft iron wire. The place where frames B, C, E and F came together was quite a vital point, and we took pains to make the wire binding at this place doubly strong. As soon as the L frame was in place we anchored the bridge to shore by running wires from the ends of the D frame and the ends of the G frame to stakes driven into the banks. The frames on the second tower were now similarly erected and anchored, after which we were ready to put in the center panels of the bridge.
The Center Panels of the Bridge.
First, the frame H was wedged into place and thoroughly fastened by a liberal winding of wire. Next the frames I and J were set in place, and in order to do this we had to remove the upper tie pieces of these frames. Then one frame was hooked in the other, and the two were carried out on the scow under the center of the bridge. Ropes were tied to the ends of the two frames, and they were lifted together, like a wide V, to the position shown in Fig. 318, after which the tie pieces were bolted on again, resting against the ends of the E frames. As an additional security, two sticks were bolted to the under side of the frame H, one at each side of the I and J frames. The bridge was then completed by wedging the frame K under the ends of the D frames, and also placing a stick across each tower under the joints of the D frames. We planned to run our gravity railway across this bridge, moving our platform and trestle to the opposite bank; so instead of flooring our bridge with slabs, we fastened ties across at intervals of 15 or 18 inches. These ties were sticks 3 inches in diameter, which were secured to the D frames.
A Serious Interruption.