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21 afther fabrication of steel members is completed in a factory,structural components are transported to the site by railroad flat cars,trucks,or barges
22then they are erected in a predetermined sequence,and the may require storage space
23for multistorey buildings,the components are usually erected in one-storey,two-storey,or even three storey tiers
24for example,the world trade center was constructed of three-storey prefabricated columns and spandrel subassemblies
25thus after the foundations are completed, the columns are raised,set on the base plates,and bolted in place
26during erection,the columns are braced laterally until the structure is completed
27after the columns are set,beams and girders are hoisted in place and temporarily bolted to the columns industrial buildings of one or two storey can be erected by small truck cranes
buildings up to 200ft(61meters)high are usually erected by larger truck cranes
28taller buildings require the use of special derricks,which are raised to the top of the completed portien of a structure as the building construction progresses upward
29self-lifting guy derricks are also used for multistorey buildings
30these derricks can jump themselves from one storey to another
31the boom serves as a gin pole to hoist the mast to a higher level
32the tower crane is more expensive than other types but has its own advantages
33the control station can be located on the crane or at a distant position that enables the operator to see the load at all times
34also the equipment can be used to place concrete and other materials directly in the form for floors and roofs,eliminating chutes,hoppers,and barrows
阅读
under present-day steel specifications,four types of fasteners are permitted for the actual beam-to-beam and beam-to-column connections commonly used in steel buildings
these are rivers,welds,unfinished bolts,and high-strength bolts
selection of the type of fastener or fasteners to be used for a particular structure usually involves many factors,including requirements of local building codes,relative economy,preference of the designer,availability of good welders or riveters,loading conditions(as static or fatigue loadings)
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