CHAPTER XIV. 

 ERECTION OF STRUCTURAL STEEL. 



METHODS OF ERECTION. The method used in erecting a steel structure will depend 

 upon the type of structure, the size of the structure, the risk to be taken, as in bridge erection, 

 \vlu-ther the structure is to be erected without interfering with traffic, as in erecting a railroad 

 bridge to replace an existing structure, or in erecting a building over furnaces or working machinery, 

 the available tools, and local conditions. The tendency of modern structural steel erection 

 practice is, as far as possible, to use derrick cars for erecting railway bridges and locomotive cranes 

 for erecting mill buildings and other structures. 



The methods of erection that may be used for erecting different steel structures are as follows. 



Plate Girders and Short Riveted Spans. Plate girders up to about 60 ft. span are very 

 commonly riveted up complete with cross frames and bracing, either at the shop oral the site, and 

 are placed in position on the abutments. With plate girders longer than 60 ft. and short riveted 

 trusses one girder or truss is placed in position at a time and the floorbeams and bracing are put 

 in place after the girders or trusses are in place. The girders or trusses may be swung into place 

 by a stiff-leg derrick or a guy derrick set up alongside the track or back of the abutment where 

 there is no track; by a derrick car, or may be hoisted into place by a gin pole. Where falsework 

 has been placed girders are picked up from the cars by two gallows frames, one near each end of the 

 span, or by one gallows frame and a derrick. Plate girders may also be put in place by sliding 

 into place either longitudinally or transversely, or by jacking and cribbing. 



Truss Bridges. Riveted trusses up to a span of 100 to 125 ft. may be riveted up on the 

 bank and be swung into place by a boom traveler or a derrick. The floorbeams and bracing 

 are then put in place and the span riveted up. Where falsework is required the bridge may be 

 erected by a gantry or outside traveler placed outside of the trusses, by a boom traveler running 

 on a track placed inside the trusses, or by a derrick car. The gantry or outside traveler is com- 

 monly used for long spans and for highway spans where no tracks are available. The boom 

 traveler is commonly used for elevated railway and highway viaducts. The derrick car is now 

 commonly used for erecting railway bridges and is sometimes used for erecting viaducts. 



. Cantilever Bridges. Cantilever bridges are commonly erected by means of an overhang 

 traveler running on the completed portion, the structure being built out from the shore. Canti- 

 lever bridges are sometimes erected on falsework in the same manner as simple trusses. 



Arch Bridges. Arches may be erected on falsework in the same manner as simple truss spans, 

 or may be cantilevered out from each abutment, the cantilever being supported by temporary 

 cables running over a tower placed back of the abutments. 



High Viaducts. High steel viaducts are commonly erected by means of an overhang or 

 boom traveler running on a track on top of the viaduct girders. The overhang or boom is long 

 enough to place a tower in advance with the traveler on the completed portion. Derrick cars 

 have also been used for erecting high steel viaducts. The towers and the girders may be erected 

 by means of gin poles. The tower bents may be bolted up before raising or may be erected and 

 bolted up in place. 



Roof Trusses, Mill and Office Buildings. Where there is sufficient room, roof trusses up 

 to 150 ft. span may be riveted or bolted up on the ground and may then be raised into position 

 by means of one or two gin poles. Two gin poles should be used for long trusses. Care should 

 be used not to cripple the lower chord. With light trusses, the lower chord members should be 

 stiffened by means of timbers or other stiff members temporarily bolted or lashed to the member. 

 Columns and beams in office buildings may be erected with stiff-leg or guy derricks, or "A" 



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