The AISC Specification for Structural Steel for Buildings, ASD and LRFD, lists allowable shear for high-strength bolts in slip-critical connections. Though there actually is not shear on the bolt shank, the shear concept is convenient for measuring bolt capacity. Since most joints in building construction can tolerate tiny slippage, bearingtype joints, which are allowed much higher shears for the same high-strength bolts when the threads are not in shear planes, may, for reasons of economy, lessen the use of slip-critical joints. The capacity of a slip-critical connection does not depend on the bearing of the bolts against the sides of their holes. Hence, general specification requirements for protection against high bearing stresses or bending in the bolts may be ignored. If the fasteners B in Fig. 7.41b are in a slip-critical connection, the bolts above the neutral axis will lose part of their clamping force; but this is offset by a compressive force below the neutral axis. Consequently, there is no overall loss in frictional resistance to slippage. FIGURE 7.43 Two main types of weldfillet and grove. Grove welds may be complete or partial

Another method of lifting wall panels employs a vacuum mata large steel mat with a rubber gasket at its edges to contact the slab. When the air between mat and panel is pumped out, the mat adheres to the panel, because of the resulting vacuum, and can be used to raise the panel. The method has the advantage of spreading pickup forces over the mat area. Panels, when erected, must be temporarily braced until other construction is in place to provide required permanent bracing. (Tilt-Up Concrete Structures, ACI 551.R, American Concrete Institute.) Joints. Joint sealants for panel installations may be mastics or elastomeric materials. These are extensible and can accommodate the movement of panels. Recommended maximum joint widths and minimum expansions for the common sealants are listed in Table 9.27. The joint sealant manufacturer should be asked to advise on backup material for use with a sealant and which shape factor should be considered. A good backup material is a rod of sponge material with a minimum compression of 30%, such as foamed polyethylene, polystyrene, polyurethane, polyvinyl chloride, or synthetic

control joints, respectively, occur in structural components of the building and along the intersection of wings of L-, U-, and T-shaped ceilings. In long walls or partitions, control joints should be inserted not more than 30 ft apart. In large ceiling areas, control joints should not be spaced more than 30 ft apart for plaster and 50 ft apart for gypsumboard. Control joints may be conveniently located along lighting fixtures, heating vents, or air-conditioning diffusers, where continuity would ordinarily be broken. Door frames extending from floor to ceiling may serve as control joints. With shorter frames, however, control joints should be inserted from the top corners of the frames to the ceiling. Installation of Joints. Where a control joint is to be provided, the continuity of gypsumboard or lath in plaster installations should be interrupted (Fig. 11.27). The gap for gypsumboard should be at least 1/2 in and for lath at least 1/4 in. A framing member should be inserted on each side of the gap to support the edges of the boards or lath. (Steel studs, however, should be fastened on only one side of the