. The design of the Chicago and Northwestern Railway train shed . ng trackcarrying box girders and suspended platform beams, with the columnsin the center of the tracks. This arrangement is the most economi-cal because long simple spans are avoided, and the bending momentis reduced to a minimum, the only live load movement being from onerail. If simple box girder beams had been used their deflectionwould cause a movement at the joints which in time would loosen therivets in the end connections. If single web girders were usedthere would be the same loosening and in addition tension on therivet
. The design of the Chicago and Northwestern Railway train shed . ng trackcarrying box girders and suspended platform beams, with the columnsin the center of the tracks. This arrangement is the most economi-cal because long simple spans are avoided, and the bending momentis reduced to a minimum, the only live load movement being from onerail. If simple box girder beams had been used their deflectionwould cause a movement at the joints which in time would loosen therivets in the end connections. If single web girders were usedthere would be the same loosening and in addition tension on the design adopted, howe-^er, the elastic curve is always horizon-tal at the columns, and therefore there is no movement or tendencyto destroy the connectionsrigidity. The box girder is the onlyone which can be built as an overhanging beam and have the rigidcolumn connections shown. To use a single web overhanding beamit would have to set on top of the coliamn and knee braces perpendi-cular to the beam would have to be employed in order to obtain a - 35 -. rigid connection. This could not be done without much work becausethe column is between the longitudinal stringers to which connec-tions would have tob e made, and also not without reducing theheadroom below. Another advantage of the box girder is that thedrainage pipes are concealed and can be easily carried to the column. It may be seen that the top flanges of the box girders aretruned in and the lower flanges turned out. The top flange isturned in so that the tops of the stringers and floor beams can beflush without coping the top flange of the stringers. The bottomflange is turned out so that it will not have to be cut in orderto admit the column and also to permit an entrance between thewebs for riveting, painting and putting in drain pipes. Diaphragmsare placed at all stringer connections so that the load will be dis-tributed to both webs and flanges making them act as one girder andbeing designed for floor beani
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