. The Street railway journal . ch heavy structures, and, onaccount of this difference, they require special is one of the most essential requirements of a well- and will have to be replaced by more substantial ones in thenear future. True economy, therefore, demands designs, good workmanship and good material. SELECTION OF A DESIGNThe kind of structure which is best adapted for a particularcrossing depends upon local conditions, such as the shapeof the profile, the width and nature of the stream, riverbottom, and the material of the approaches. If a struct
. The Street railway journal . ch heavy structures, and, onaccount of this difference, they require special is one of the most essential requirements of a well- and will have to be replaced by more substantial ones in thenear future. True economy, therefore, demands designs, good workmanship and good material. SELECTION OF A DESIGNThe kind of structure which is best adapted for a particularcrossing depends upon local conditions, such as the shapeof the profile, the width and nature of the stream, riverbottom, and the material of the approaches. If a structure isto span a valley with only a small creek, a viaduct consistingof braced steel towers and plate girder spans is generally themost suitable structure. If the viaduct, instead of crossingthe valley, is located in the streets of a city where the towerbracing would interfere with the traffic in the street, thisbracing has to be omitted and the spans supported on columnsin which brackets take the place of the bracing to insure. SCHUYLKILL RIVER BRIDGE AT FALLS OF SCHUYLKILL, rillLADELrillA, PA. designed structure. A railroad bridge, owing to the natureof the traffic it has to carry, requires heavy members andconnections, and this massiveness alone imparts considerablerigidity to the structure. On the other hand, a bridge carry-ing an electric railway is generally a much lighter structureand has not the natural advantage of that rigidity producedby its own weight; the same must, therefore, be obtained bythe design. The designing and building of a bridge or any other struc-ture on the strength of which human life depends cannot betoo well or carefully done. In accordance with the writersexperience and oljservations, electric railway bridges gener-ally are not designed with the same care as railroad are, as a rule, treated like county highway bridges, care-lessly designed, sometimes by incompetent men, and built inshops fitted up to do only the ordinary class of highw
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
