Dimensional tolerances for precast members and tolerances on fitting of precast members vary for type of member, type of joint, and conditions of use. See PCI TABLE 9.26 Minimum Reinforcement Cover for Precast Members, in Concrete exposed to earth or weather: Wall panels: No. 14 and No. 18 bars 11/2 No. 11 bars and smaller 3/4 Other members: No. 14 and No. 18 bars 2 No. 6 through No. 11 bars 11/2 No. 5 bars, 5/8-in wire and smaller 11/4 Concrete not exposed to weather or in contact with the ground: Slabs, walls, joists: No. 14 and No. 18 bars 11/4 No. 11 bars and smaller 5/8 Beams, girders, columns: Principal reinforcement: Diameter of bar db but not less than 5/8 in and need not be more than 11/2 in Ties, stirrups or spirals 3/8 Shells and folded-plate members: No. 6 bars and larger 5/8 No. 5 bars, 5/8-in wire and smaller 3/8 Design Handbook, and Design and Typical Details of Connections for Precast and Prestressed Concrete, Precast / Prestressed Concrete Institute; and Standard Specifications for Tolerances for Concrete Construction and Materials, ACI 117, American Concrete Institute. For strength and durability, precast concrete members require adequate curing. They usually are given some type of accelerated curing for economic reuse of forms and casting space. At atmospheric pressure, curing temperatures may be held between 125 and 185F for 12 to 72 h. Under pressure, autoclave temperatures above 325F for 5 to 36 h are applied for fast curing. Casting temperatures, however, should not exceed 90F. See Fig. 9.5. (Standard Practice for Curing Concrete, ACI 308; Accelerated Curing of Concrete at Atmospheric PressureState of the Art, ACI 517.2R, American Concrete

diameter, in Diameter of standard hole Diameter of oversize hole Short-slot hole (width
length) Long-slot hole (width
length) 11/8 d  1/16 d  5/16 (d  1/16)
(d  3/8) (d  1/16)
(2.5
d) * Approval of the designer is required for use of oversize or slotted holes. Larger holes than those listed in the table, if required for tolerance in location of anchor bolts in concrete foundations, may be used in column base details. loading. Washers, hardened when used with high-strength bolts, should be placed over oversize and short-slot holes. Long-slot holes may be used in only one ply of the connected parts at an individual faying surface. When the slot is in an outer ply, plate washers or a continuous bar with standard holes should be installed to cover the entire slot. Washers or bars for A325 or A490 bolts should be 5/16 in or more thick but need not be hardened. If hardened washers are required, they should be placed over the outer surface of a plate washer or bar. 7.30.2 LRFD for Bolts The design strength of bolts or threaded parts is Rn (tabulated in Table 7.26) applied to the nominal body area of bolts and threaded parts except upset rods (see footnote h for Table 7.26). The applied load is the sum of the factored external loads plus the tension, if any resulting from prying action caused by deformation of connected parts. If high-strength bolts are required to support the applied loads by direct tension, they should be proportioned so that the average required strength (not including initial bolt tightening force) applied to the nominal bolt area will not exceed the design strength. The design strength in tension for a bolt or threaded part subject to combined tension and shear stresses is also listed in Table 7.26. The value of v, the shear caused by the factored loads producing tensile stress, should not exceed the values for shear alone given in Table 7.26. Table 7.25 lists maximum dimensions for standard, oversize, and slotted bolt holes. The limitations on these are the same as those for ASD (Art. 7.26.1). The design bearing strength at a bolt hole may be taken as Rn  3.0dtFu, or with   0.75, as 2.25dtFu, where d is the nominal bolt diameter, t is the thickness of the connected part, and Fu is the tensile strength of the connected part. For welds joining structural steel elements, the load capacity depends on type of weld, strength of electrode material, and strength of the base metal. Fillet or groove TABLE 7.26 Design Strength, ksi, for Bolts and Threaded Parts

It is essential that bridging be installed between joists as soon as possible after the joists are placed and before application of any construction loads. The most commonly used type of bridging is continuous horizontal bracing composed of steel rods fastened perpendicular to the top and bottom chords of the joists. Diagonal bridging, however, is also permitted. The attachment of the floor or roof is expected to provide additional support of the joists against lateral buckling. It is important that masonry anchors be used on wall-bearing joists. Where the joists rest on steel beams, they should be welded, or clipped to the beams. Plastered ceilings attached directly to regular open-web steel joists are usually supported at underslung ends by means of ceiling extensions, as shown in Fig. 8.24a. Extended ends, as shown in Fig. 8.24b, allow floor and roof treatments beyond outer supporting stringers. Relatively small openings between joists may usually be framed with angle, channel, and Z-shaped headers supported on adjacent joists. Larger openings should be framed in structural steel. Headers should preferably be located so that they are supported at trimmer-joist panel points.