. Details of riveted railroad truss bridges . e or outside of the lower chord,according to the make-up of its section. Art. 7. Diagonals. In order to make a bridge rigid it is necessary to havediagonals in each panel. These are designed to taketension in some bridges and compression in others. The diagnolsnear the centre of the bridge are called on to take a reversal ofstresses due to the total shear changing from positive to neg-ative or vis-a-versa. To prevent this reversal a counter isplaced in the bridge. This counter consists of another diagonalplaced in the opposite direction
. Details of riveted railroad truss bridges . e or outside of the lower chord,according to the make-up of its section. Art. 7. Diagonals. In order to make a bridge rigid it is necessary to havediagonals in each panel. These are designed to taketension in some bridges and compression in others. The diagnolsnear the centre of the bridge are called on to take a reversal ofstresses due to the total shear changing from positive to neg-ative or vis-a-versa. To prevent this reversal a counter isplaced in the bridge. This counter consists of another diagonalplaced in the opposite direction from the main diagnals. In themiddle panel and the panels adjacent to it there are usuallycounters, -37- The sections used for the counters or diagonals aresimilar to those used for verticals. The two common forms beingthe two-channels-and lattice-bars section and the section com-posed of two pair of angles and lattice bars. Where a heavydiagonal is used no counter is employed because the heavydiagonal can take either tension or The method used for fastening the diagonals to theupper and lower chord is simple. It consists of using a largegusset plate ccnnectei to the intermediate posts,and to thisplate the diagonals are riveted. There is a little latitude in design where the counterdiagonals are used on account of the diagonals crossing. Onemethod for this is in the case shown by Here the diagonals are made up of two angles placed back to back and riveted atintervals along their length. One diagonal is riveted along theoutside of the gusset plate on both chords while the other oneis riveted on the inside. At their intersection they are riveteto each other. Sometimes directly and sometimes by putting asmall plate between the two pairs of angles. It is preferable t 38 have this small plate in order to keep the counters straight. Another common form of intersection is shown by large plate is used at the intersection and the counter diagonalis broken.
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