(9.78) 1  (2/3)
b /b 1 2 v
(1  ) (9.79) where b1
width of critical section measured in the direction in which moments are being determined b2
width of critical section measured in the direction perpendicular to b1 For a square edge column and square panels, approximately 60% of the unbalanced moment will be transferred by flexure within the slab width (c2  3h) centered on the column centerline. The result is that about 60% of the total top reinforcement required in the column strip must be concentrated within the slab width (c2  3h) at the edge column. The designer must ensure that the top reinforcing bars selected can be physically fitted into the width (c2  3h) within allowable bar spacings, and clearly show the bar spacings and details on the design drawings. For transfer of gravity load moment from the slab to the edge column by eccentricity of shear, the Code prescribes v(0.3 Mo) as the magnitude of the moment to be transferred, rather than vMu, where Mo is calculated by Eq. (9.72). For preliminary design, with square columns flush at edges of the flat plate, a rapid estimate of the shear capacity to allow for effects of combined shear due to gravity loads and to moment transfer can be made by using uniform vertical load wu only, with nominal strength for factored load as follows: For edge column, total shear Vu
0.5wuL2L1 and shear strength Vc
2 bod

c For first interior column, Vu
1.15wuL2L1 and shear strength Vc
bod 4

c where
specified concrete compressive strength, psi.
c Use of this calculation in establishing a preliminary design is a short cut, which will often avoid the need for repeating steps 1 through 5 in Art. 9.59.1, because it gives a close approximation for final design. The minimum cantilever edge span of a flat plate so that all columns can be considered interior columns and the direct-design method can be used without tedious stiffness calculations is 4/15 of the length of the interior span (Fig. 9.29). This result is obtained by equating the minimum cantilever moment at the exterior column to the minimum negative-factored moment at the interior column. FIGURE 9.29 Length of cantilever (at left) determines whether the exterior column may be treated as an interior

Outlet Blanked outlet Drop cord Electrical outlet-for use only when circle used alone might be confused with columns, plumbing symbols, etc. Fan outlet Junction box Lamp holder Lamp holder with pull switch Pull switch Outlet for vapor-discharge lamp Exit-light outlet Clock outlet (specify voltage) Duplex convenience outlet Convenience outlet other than duplex. 1
single, 3
triplex, etc. Weatherproof convenience outlet Range outlet Switch and convenience outlet Radio and convenience outlet Special-purpose outlet (designated in specifications) Floor outlet Single-pole switch Double-pole switch Three-way switch Four-way switch Automatic door switch Electrolier switch Key-operated switch Switch and pilot lamp Circuit breaker Weatherproof circuit breaker Momentary-contact switch Remote-control switch Weatherproof switch Fused switch Weatherproof fused switch TABLE 15.1 Electrical Symbols* (Continued) Wall Ceiling Any standard symbol as given above with the addition of a lower-case subscript letter may be used to designate some special variation of standard equipment of particular interest in a specific set of architectural plans. When used, they must be listed in the key of symbols on each drawing and if necessary further described in the specifications

Another form of preengineered, preassembled, lightweight wood truss, commonly referred to as a composite wood-metal truss, consists of lumber chords and steel webs. One type uses metal-angle webs with nail plates formed on each end. At a joint, the teeth of the nail-plate end are pressed into a wood chord. Another configuration of composite wood-metal truss uses steel tubular web members, which are joined to the wood chords with patented steel-pin connections. The chords are typically machine stress-rated lumber or laminated veneer lumber (Art. 10.30.4). Because of the proprietary nature and uniqueness of the various types of composite wood-metal trusses, design data should be obtained from the manufacturers. (See K. F. Faherty and T. G. Williamson, Wood Engineering and Construction Handbook, McGraw-Hill Publishing Company, New York, for additional information.) 10.22.2 Heavy Timber Trusses Type of heavy timber truss and arrangement of members may be chosen to suit the shape of structure, the loads, and stresses involved. The configuration most commonly used are bowstring, flat or parallel chord, pitched, triangular, and scissors (Fig. 10.17) For most commercial construction, trusses usually are spaced 8 to 24