manufacturers standard gage No. Weight, psf Equivalent sheet thickness, in* Galvanized sheet gage No. Weight, psf Thickness equivalent, in * Thickness equivalents of steel are based on 0.023912 in / (lb-ft2) (reciprocal of 41.820 psf per inch of thickness, although the density of steel is ordinarily taken as 489.6 lb / ft3, 0.2833 lb / in3, or 40.80 psf per inch of thickness). The density is adjusted because sheet weights are calculated for specified widths and lengths of sheets, with all shearing tolerances on the over side, and also because sheets are somewhate thicker at the center than at the edges. The adjustment yields a close approximation of the relationship between weight and thickness. (Steel Products Manual, Carbon Steel Sheets, American Iron and Steel Institute.) Total thickness, in, including zinc coating. To obtain base metal thickness, deduct 0.0015 in per ounce coating class, or refer to ASTM A653. for shapes in which bends and corners constitute a high percentage of the whole section, cold working increases the overall strength more than for shapes having a high proportion of thin, wide, flat elements that are not heavily worked in forming. For the latter type of shapes, the strength of the plain, unformed sheet or strip may be the controlling factor in the selection of a grade of material. Full-section tests constitute a relatively simple, straightforward method of determining as-formed strength. They are particularly applicable to sections that do not contain any elements that may be subject to local buckling. However, each case has to be considered individually in determining the extent to which cold forming will produce an increase in utilizable strength. For further information, refer to the AISI Specification for the Design of Cold-Formed Steel Structural Members and its Commentary, 1996, American Iron and Steel Institute, 1101 17th St., NW, Washington, DC 20036. Many cold-formed shapes used for structural purposes are similar in their general configurations to hot-rolled structural sections. Channels, angles, and zees can be roll-formed in a single operation from one piece of material. I sections are usually made by welding two channels back to back or by welding two angles to a channel. All sections of this kind may be made with either plain flanges as in Fig. 8.1a to d, j, and m or with flanges stiffened by means of lips at outer edges, as in Fig. 8.1e

All the types of screws shown in Fig. 8.12 require prepunched or predrilled holes. Self-drilling screws, which have a twist drill point that drills the proper size of hole just ahead of threading, are especially suited for field work, because they eliminate separate punching or drilling operations. Another type of self-drilling screw, capable of being used in relatively thin sheets of material in situations where the parts being joined can be firmly clamped together, has a very sharp point that pierces the material until the threads engage. TABLE 8.12 Average Diameters of Self-Tapping Screws, in* Number or size, in Types AB and B Outside Root Type F Outside Type U Outside No. 4 0.112 0.084 0.110 0.114 No. 6 0.137 0.102 0.136 0.138 No. 8 0.164 0.119 0.161 0.165 No. 10 0.186 0.138 0.187 0.180 No. 12 0.212 0.161 0.213 0.209 No. 14 or 1/4 0.243 0.189 0.247 0.239 *Averages of standard maximum and minimum dimensions adopted under ANSI B18.6.4-1966. Type F has threads of machine-screw type approximating the Unified Thread Form (ANSI B1.101960). The figures shown are averages of those for two different thread pitches for each size of screw. Size No. 14 for Type U. Does not apply to Type AB. Torsional-strength requirements for self-tapping screws have been standardized under American National Standards Institute B18.6.4, Slotted and Recessed Head Tapping Screws and Metallic Drive Screws. Safe loads in shear and tension on such screws can vary considerably, depending on type of screw and head, tightening torque, and details of the assembly. When screws are used for structural loadcarrying purposes, the user should rely on experience with the particular application, manufacturers recommendations, or actual tests of the type of assembly involved. Essential body dimensions of some types of self-tapping screws are given in Table 8.12. Complete details on these and other types, and recommended hole sizes, may be found in ANSI B18.6.4 and in manufacturers publications. Special fasteners, such as tubular rivets, blind rivets (capable of being driven from one side only), special bolts used for blind insertion, special studs, lock nuts, and the like, and even metal stitching, which is an outgrowth of the common office stapling device for paper, are used for special applications. When such a fastener is required, refer to manufacturers catalogs for design information, and base any structural strength attributed to the fastener on the results of carefully made tests or the manufacturers recommendations. Steel roof deck consists of ribbed sheets with nesting or upstanding-seam joints designed for the support of roof loads between purlins or frames. A typical roof- FIGURE 8.13 Roof-deck assembly. FIGURE 8.14 Typical cold-formed steel roof-deck sections. (a) Narrow rib: (b) intermediate rib; (c) wide rib; (d ) intermediate rib in 36-in-wide sheets with nested side laps; (e) wide rib in 32-inwide sheets with upstanding seams. deck assembly is shown in Fig. 8.13. The Steel Deck Institute, P.O. Box 25, Fox River Grove, IL 60021, has developed much useful information on steel roof deck. Various types of steel roof deck are available and may be classified in accordance with recommendations of the Steel Deck Institute (SDI). All types consist of long, narrow sections with longitudinal ribs at least 11/2 in deep and spaced about 6 in on centers (Fig. 8.14). Other rib dimensions are shown in Fig. 8.14a to c for some

Glossy-smooth concrete finish can be obtained with forms made of plastic. But, for exterior exposure, this finish left untreated undergoes gradual and nonuniform loss of its high reflectivity. Textured surfaces or smooth but nonglossy surfaces obtained by early form removal are preferred for exterior exposure. Exposed-aggregate monolithic finishes can be obtained with horizontal-cast panels by initially casting a thin layer containing the special surface aggregates in the forms and then casting regular concrete backup. With a thickness of exposed aggregate of less than 1 in, the panel can also be cast face up and the aggregate seeded over the fresh concrete or hand placed in a wet mortar. Variations of exposed surface can be achieved by use of set retardant, acid washes, or sandblasting. Consolidation of the concrete in the forms to obtain good appearance and durability can be attained by one of the following methods: External vibration with high-frequency form vibrators or a vibrating table. Internal or surface vibration with a tamping-type or jitterburg vibrator. Placing a rich, high-slump concrete in a first layer to obtain uniform distribution of the coarse aggregate and maximum consolidation, and then making the mix for the following layers progressively stiffer. This allows absorption of excessive water from the previous layer. Tilt-up panels can be economical if the floor slab of the building can be designed for and used as the form for the panels. The floor slab must be level and smoothly troweled. Application of a good bond-breaking agent to the slab before concrete is cast for the panels is essential to obtain a clean lift of the precast panels from the floor slab. If lifting cables are attached to a panel edge, large bending moments may develop at the center of the wall. For high panels, three-point pickup may be used. To spread pickup stresses, specially designed inserts are cast into the wall at pickup