Application of wall membranes should he started at the bottom of one end of the wall and the strips of fabric or felt laid vertically. Preparation of the surfaces and laying of the membrane proceed much as they do with floor membranes. The surfaces to which the membrane is attached must be dry and smooth, which may require that the faces of masonry walls be leveled with a thin coat of grout or mortar. The plies of the wall membrane should be lapped into those of the floor membrane. If the outside method of application is used and the membrane is faced with masonry, the narrow space between the units and the membrane should be filled with mortar as the units are laid. The membrane may be terminated at the grade line by a return into the superstructure wall facing. Waterstops in joints in walls and floors containing a bituminous membrane should be the metal-bellows type. The membrane should be placed on the exposed face of the joint and it may project into the joint, following the general outline of

In inflated dual-walled construction, pressurized air is trapped between two concentric membranes (Fig. 5.106). The shape of the inner membrane is maintained by suspending it from the outer one. Because of the large volume of air compressed between the membranes, this type of construction can span longer distances than can inflated-rib structures. Because of the variation of air pressure with changes in temperature, provision must be made for adjustment of the pressure of the compressed air in air-inflated structures. Air must be vented to relieve excessive pressures, to prevent overtensioning of the membranes. Also, air must be added to compensate for pressure drops, to prevent collapse. Air-supported enclosures consist of a single membrane supported by the difference between internal air pressure and external atmospheric pressure (Fig. 5.107). The pressure differential deflects the membrane outward, inducing tensile stresses in it, thus enabling it to withstand compressive forces. To resist the uplift, the construction must be securely anchored to the ground. Also, the membrane must be completely sealed around its perimeter to prevent air leakage. Hybrid structures consist of one of the preceding types of pneumatic construction augmented by light metal framing, such as cables. The framing may be merely a safety measure to support the membrane if pressure should be lost or a means of shaping the membrane when it is stretched. Under normal conditions, air pressure against the membrane reduces the load on the framing from heavy wind and snow

TABLE 8.9 Nominal Bearing Stresses for Bolted Connections of Cold-Formed Steel Componentsa Type of joint Nominal bearing stress Fp, ksi With washers under both bolt head and nutb Without washers under bolt head and nut or with only one washer c Inside sheet of double-shear connection 3.33Fu (Fu /Fsy 1.08)d 3.00Fu (Fu /Fsy  1.08)d 3.00Fu e Sheets in single shear and outside sheets of doubleshear connection 3.00Fu 2.22Fu e aFor joints with parts 3/16 in or more thick, see the Specification for Structural Steel Buildings, American Institute of Steel Construction. bFor joints with parts 0.024 in or more thick. cFor joints with parts 0.036 in or more thick. dFu /Fsy is the ratio of the tensile strength of a connected part to its yield strength. e For Fu /Fsy 8.18.4 ExampleTension Joints with Two Bolts Assume that the bolted tension joints of Fig. 8.11 comprise two sheets of 3/16-inthick, A611, Grade C steel. For this steel, Fsy
33 ksi and Fu
48 ksi. The sheets in each joint are 4 in wide and are connected by two 5/8-in-diameter, A325 bolts, with washers under both bolt head and nut. Case 1 of Fig. 8.11 has the two bolts arranged in a single transverse row. A force T/2 is applied to each bolt and the total force T has to be carried by the net section of each sheet through the bolts. So, in Eq. (8.45), r
2(T/2) /T
1. Spacing of the bolts s
2 in and d/ s
5/8/2
0.312. The tension stress in the net section, computed from Eq. (8.45), is then F
(1  0.9  1  3  1  0.312)F
1.04 F  F t u uu