IEEE 951-1996(R2009) pdf free download – IEEE Guide to the Assembly and Erection of Metal Transmission Structures
5.3 Constructability of structures
Construction can be enhanced by a number of considerations, both in the design of the structure and in detailing of the connections. It should be noted that these considerations could increase material costs, although these costs may be offset by reduced field costs and improved safety. The following are applicable to all types of metal structures:
a) Each member should be clearly and permanently marked by stamping or welding. This mark should be legible after any coatings are applied to facilitate identification and possible field replacement. These permanent markings should be visible after the structure is erected. Stencilling with water- proof paint will further facilitate field identification; however, care should be taken to avoid adverse visual impact. See 6.4 regarding stencilling of weathering steel. ldentification marks may include the following information: General location of the member in the structure by using a logical numbering sequence 2) Structure type Special material types
b) The structure should be designed with a minimal assortment of bolt diameters and types.
c) Adequate clearance around nuts and bolt heads for wrenches or sockets should be provided.
d) For safety and ease of erection, a place for a worker to stand should be provided below each leg splice. As an example, two step bolt holes could be provided 1.37 m (4 ft, 6 in) below each splice for optional step bolts.
e) The bill of materials should provide an approximate finished (that is, galvanized or painted) weight of each structure item (that is, members, plates, flls, bolts, and nuts) in order to determine the loads to be lifted.
f)Legible erection drawings and data sheets for line sections should be provided. The drawings should show the member mark identification, bolt size, and length, bolt pattern, orientation of angle mem-bers, and whether a member is inside or outside its connecting member (that is, use hidden lines anddetailed or enlarged views). In addition, these erection drawings should show the rigging attachmentpoints identified in 5.le).
g)Fabrication tolerances that are either too restrictive or too liberal can result in increased field costs.h)Consideration should be given to the method of locking fasteners.The method selected will influ-ence construction efficiency. Typical methods and devices are lock nuts，lock washers， pal nuts,punched threads, weathering steel, etc.
i) Designs should be checked for worker accessibility. Design of structures sometimes results in largespaces between members, making it difficult for workers to reach the joints. In such cases, it may benecessary to lift workers to install or check bolts.
5.3.1 Constructability of lattice structures
Considerations specific to lattice structures include the following:
a) Where members are connected by one bolt at each end, the detailer should require a spud hole at thelower or main leg end. The tapered end of a spud wrench or drift pin is inserted into this hole tofacilitate positioning of the member. This hole should be indicated as a spud hole on the erectiondrawing. The spud hole may indicate that the member was detailed slightly short in order to intro-duce prestress into the member. Spud holes in weathering steel should be bolted tight.
b) Depending on the method of erection, the location of leg and crossarm splices can affect the assem-bly and future maintenance of the structure. Leg splices located above the crossarm hanger or belowthe chord of the crossarm (not between them) will facilitate aerial erection as shown in Figure 2. Ifthe structure is assembled on the ground, the leg splices may be located between the crossarmhanger and crossarm chord as shown in Figure 3.Acrial erection can also be helped if leg splices arelocated just above horizontal bracing as shown in Figure 4.This helps to maintain proper geometryand structural integrity of the lower body.
Crossarm and ground wire peak splices located outside the body of the structure，as shown inFigure 2, may facilitate aerial assembly. In addition, arm and ground wire peaks can be removed orreplaced without affecting the integrity of the remaining structure if their splices are located asshown in Figure 2, as opposed to Figure 3.
c) When tilting up structure sections diagonal braces extending below the main legs can be damaged.Two possible solutions are shown in Figures 5 and 6. The method shown in Figure 5 is necessarywhen helicopter erection is planned. The method shown in Figure 6 has the advantage of requiringno additional permanent material and is suitable for crane erection only.