The shear V, kips, at any section should not exceed the allowable shear Va, kips, calculated as follows: For h/ t  0.96kvE/Fy, V
0.4F ht (8.17) a y For 0.96kvE/Fy  h/ t  1.415kvE/Fy , V
0.38t 2k EF (8.18) a v y For h/ t  1.415kvE/Fy , V
0.54k Et 3 /h (8.19) a v where t
web thickness, in h
depth of the flat portion of the web measured along the plane of the web, in E
modulus of elasticity of the steel
29,500 ksi kv
shear buckling coefficient
5.34 for unreinforced webs for which (h/ t) does not exceed 200 max Fy
specified yield stress of the steel, ksi For design of reinforced webs, especially when h/ t exceeds 200, see AISI Specification for the Design of Cold-Formed Steel Structural Members. For a web consisting of two or more sheets, each sheet should be considered as a separate element carrying its share of the shear. For beams with unreinforced webs, the moment M and shear V should satisfy the following interaction equation: (M/M )2  (V/V )2  1.0 (8.20) axo a where Maxo
allowable moment about the centroidal axis, in-kips, when bending

FIGURE 7.17 Typical wind connections for beams to columns. Moment-Resisting Frames. Designers have a choice of several alternatives to X bracing. Knee braces, shown in Fig. 7.16d, or portal frames, shown in Fig. 7.16e, may be used in outer walls, where they are likely to interfere only with windows. For buildings with window walls, the bracing often used is the bracket type (Fig. 7.16). It simply develops the end connection for the calculated wind moment. Connections vary in type, depending on size of members, magnitude of wind moment, and compactness needed to comply with floor-to-ceiling clearances. Figure 7.17 illustrates a number of bracket-type wind-braced connections. The minimum type, represented in Fig. 7.17e, consists of angles top and bottom: They are ample for moderate-height buildings. Usually the outstanding leg (against the column) is of a size that permits only one gage line. A second line of fasteners would not be effective because of the eccentricity. When greater moment resistance is needed, the type shown in Fig. 7.17b should be considered. This is the type that has become rather conventional in field-bolted construction. Figure 7.17c illustrates the maximum size with beam stubs having flange widths that permit additional gage lines, as shown. It is thus possible on larger wide-flange columns to obtain 16 fasteners in the stub-to-column connection. The resisting moment of a given connection varies with the distance between centroids of the top and bottom connection piece. To increase this distance, thus increasing the moment, an auxiliary beam may be introduced as shown in Fig. 7.17d, if it does not create an interference. All the foregoing types may be of welded construction, rather than bolted. In fact, it is not unusual to find mixtures of both because of the fabricators decision to shop-bolt and field-weld, or vice versa. Welding, however, has much to offer in simplifying details and saving weight, as illustrated in Fig. 7.17e, , and g. The last represents the ultimate efficiency with respect to weight saving, and furthermore, it eliminates interfering details. Deep wing brackets (Fig. 7.17h and i) are sometimes used for wall beams and spandrels designed to take wind stresses. Such deep brackets are, of course, acceptable for interior beam bracing whenever the brackets do not interfere with required clearances. Not all beams need to wind-braced in tall buildings. Usually the wind load is concentrated on certain column lines, called bents, and the forces are carried through the bents to the ground. For example, in a wing of a building, it is possible to concentrate the wind load on the outermost bent. To do so may require a stiff floor or diaphragm-like system capable of distributing the wind loads laterally. Onehalf these loads may be transmitted to the outer bent, and one-half to the main building to which the wing connects. Braced bents are invariably necessary across the narrow dimension of a building. The question arises as to the amount of bracing required in the long dimension, since wind of equal unit intensity is assumed to act on all exposed faces of structures. In buildings of square or near square proportions, it is likely that braced bents will be provided in both directions. In buildings having a relatively long dimension, as compared with width, the need for bracing diminishes. In fact, in many instances, wind loads are distributed over so many columns that the inherent rigidity of the whole system is sufficient to preclude the necessity of additional bracing. Column-to-column joints are treated differently for wind loads. Columns are compression members and transmit their loads, from section above to section below, by direct bearing between finished ends. It is not likely, in the average building, for the tensile stresses induced by wind loads ever to exceed the compressive pressure due to dead loads. Consequently, there is no theoretical need for bracing a column joint. Actually, however, column joints are connected together with nominal splice plates for practical considerationsto tie the columns during erection and to obtain vertical alignment. This does not mean that designers may always ignore the adequacy of column splices. In lightly loaded structures, or in exceptionally tall but narrow buildings, it is possible for the horizontal wind forces to cause a net uplift in the windward column because of the overturning action. The commonly used column splices should then be checked for their capacity to resist the maximum net tensile stresses caused in the column flanges. This computation and possible heaving up of the splice material may not be thought of as bracing; yet, in principle, the column joint is being wind-braced in a manner similar to the wind-braced floor-beam connections.

There are three methods for tightening bolts to assure the prescribed tensioning: Turn-of-Nut. By means of a manual or powered wrench, the head or nut is turned from an initial snug-tight position. The amount of rotation, varying from one-third to a full turn, depends on the ratio of bolt length (underside of heat to end of point) to bolt diameter and on the disposition of the outer surfaces of bolted parts (normal or sloped not more than 1:20 with respect to the bolt axis). Required rotations are TABLE 7.5 Washer Requirements for High-Strength Bolts Method of tensioning A325 bolts A490 bolts Base material Fy  40.0* Base material Fy  40.0* Calibrated wrench One washer under turned element Two washers One washer under turned element Turn-of-the-nut None Two washers One washer under turned element Both methods, slotted and oversized holes Two washers Two washers Two washers *Fy  specified minimum yield stress, ksi. TABLE 7.6 Minimum Tightening Tension, kips, for High-Strength Bolts