tailieunhanh - Steel Designer's Manual Part 14

Tham khảo tài liệu 'steel designer's manual part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Steel Designers Manual - 6th Edition 2003 This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12 2 2007 To buy a hardcopy version of this document call 01344 872775 or go to http Cranes and craneage 993 Mobility for non-mobile cranes Non-mobile cranes can be made mobile by mounting them on rails. This has two advantages the positioning of the crane can be more easily dictated and controlled and the loads transmitted by the rails to the ground act in a precisely known location. Many cranes have collapsed because of insufficient support underneath. However most rail-mounted crane failures have occurred from overloading. Where the crane is to work over complex plant foundations the rail can be carried on a beam supported if necessary on piles especially driven for the purpose. If the rail is supported only by a beam on sleepers in direct contact with the ground the load can be properly distributed by suitable spreaders. In either case conditions must be properly considered and designed for. Problems often occur when too much faith is invested in the capability of the ground to support a mobile crane and its outriggers. Non-mobile cranes Non-mobile cranes are generally larger than their mobile counterparts. They can reach a greater height and are able to lift their rated loads at a greater radius. There are two main types of non-mobile crane the tower crane and the now rare derrick. Due to their great size the cranes must arrive on site in pieces. Thus the disadvantage of a non-mobile crane is that it has to be assembled on site. Having been assembled the crane must receive structural winch and stability tests before being put into service. A tower crane with sufficient height and lifting capacity see Fig. has several advantages 1 It requires only two rails for it to be mobile .These two rails although at a wide gauge take up less ground space than a derrick. 2 It carries most of .