442 



ERECTION OF STRUCTURAL STEEL. 



CHAP. XIV. 



derricks may be used for loads up to 5 tons. The bents of steel mill buildings may be erected in 

 the same manner. Roof arches and train sheds are sometimes erected by means of falsework, 

 which is moved as the erection proceeds. Boom-tower derricks running on tracks are found 



(a) CRAB 



(b) WINCH 



^Boiler 



(Spool, or 

 A Winch, or 

 \ A \N/ggerHe3d 



(c) DERRICK CRAB (d) HOISTING ENGINE 



FIG. i. HOISTS FOR STEEL ERECTION. 



very convenient. Locomotive cranes are now used for erecting mill buildings and similar struc- 

 tures where tracks are available. 



Elevated Towers and Tanks. The towers for high tanks are commonly erected by means 

 of a gin pole. A gin pole long enough to erect the entire tower may be used, or short gin poles 

 may be lashed to the part of the tower already erected ; the gin poles being moved up as the erection 



