Bolted connections of cold-formed steel members are designed as bearing type connections.
Bolt pretensioning is not required and installation should be to the snug-tight condition. The AISI Specification gives applicable provisions when the thickness, t, of the thinnest connected part is less than 3â„16 in (4.76 mm). For thicker members, the AISC Specification applies. The most commonly used grades are A307 carbon steel bolts and A325 high strength bolts, but other types can also be used. Standard hole diameter is d + 1â„32 in for d mm for d < 12.7 mm) where d is bolt diameter. Standard hole diameter is d + 1â„16 in for d => 1â„2 in (d + 1.6 mm for d => 12.7 mm). See the AISI Specification for information on slotted holes.
Several conditions must be checked for a bolted connection, including shearing strength of sheet (edge distance and spacing effects), tension strength in each connected part, bearing strength, bolt shear strength, and bolt tension strength. Each of these is treated in the following articles.
Sheet Shearing (Spacing and Edge Distance)
If bolts are too close to the ends of members, or if the bolts are spaced too closely, the connection may be limited in strength by the shear strength along a line parallel to the member force. Minimum center-to-center spacing of bolts is 3d and minimum center-to-edge distance is 1.5d. Additionally, the nominal strength, Pn, is limited to
where t = thickness of thinnest part and e = distance in line of force from center of hole
to nearest edge of adjacent hole or end of connected part.
Tension in Connected Part
For components in tension, limit states of both yielding and fracture must be considered,
with the smaller value controlling. The nominal tension strength, Pn, on the net section, An,
of each connected part must not exceed
The bearing strength varies from to Pn = 2.22Fudt to Pn = 3.33fudt depending on whether washers are used, the type of joint, and the Fu /Fsy ratio of the connected part. The AISI provisions are summarized in Tables 10.5 and 10.6.
Shear and Tension in Bolts
The nominal bolt strength resulting from shear, tension, or a combination thereof is calculated as follows: