466 



ERECTION OF STRUCTURAL STEEL. 



CHAP. XIV. 



TABLE XL 



LIST OF TOOLS FOR THE ERECTION OF SO-FT. SPAN HIGHWAY BRIDGE. 

 MINNEAPOLIS STEEL & MACHINERY Co. 



ERECTION OF TRUSS BRIDGES. Truss bridge spans are usually erected on falsework. 

 The truss may be erected by means of a traveler or a derrick traveler or a derrick car. The usual 

 procedure where a traveler is used will be briefly described. After the falsework and traveler are 

 ready, lay out the center lines of the trusses on the falsework and locate the positions of the panel 

 points. At each panel point place the necessary blocking for camber. Then beginning at the 

 fixed end place the pedestals in position and place the lower chords and the floorbeams and stringers 

 in position and distribute the pins. If the floorbeams and stringers will be in the way they are 

 not placed until they are needed. The traveler is run to the center of the bridge and the center 

 panel on each side is erected. The upper chord section is hoisted and held a little above its final 

 position; the posts are raised, the diagonals are put in place and the pins are driven, or with a 

 riveted truss the joints are field bolted in about 50 per cent of the holes. The panel on the oppo- 

 site side is then erected and the top lateral struts and bracing are put in place, the floorbeams and 

 stringers are connected up and the lower laterals are put in place, so that the center tower is fully 

 braced. Great care must be used in erecting the middle tower to see that it is in exactly the 

 proper place. After the center panel is complete the traveler is moved toward the fixed end, 

 erecting the trusses one panel at a time. The traveler is then run back to the center and the 

 roller end of the trusses are erected. After the span is all connected up and all connections are 

 properly bolted up, the blocking is knocked out and the bridge is swung clear. The details of 

 erection vary with the type of truss and local conditions .and the above description is intended to 

 merely give an idea of the procedure. Truss bridges may also be erected by starting the 

 traveler at the fixed end. 



Where a derrick car or a derrick traveler is used the erection is commonly started at the 

 fixed end. 



