Bolts are the preferred method for site assembly of framed building
components, although rivets have been popular in the past and will
be found when working on existing buildings. Cold driven and `pop'
rivets may be used for factory assembly of light steel frames such
as stud walling, but the traditional process of hot riveting
structural steel both in the workshop and on site has largely been
superseded for safety reasons and the convenience of other
practices.
Types of Bolt ~
- Black Bolts ~ the least expensive and least precise type of
bolt, produced by forging with only the bolt and nut threads
machined. Clearance between the bolt shank and bolt hole is
about 2 mm, a tolerance that provides for ease of assembly.
However, this imprecision limits the application of these bolts
to direct bearing of components onto support brackets or
seating cleats. - Bright Bolts ~ also known as turned and fitted bolts. These
are machined under the bolt head and along the shank to
produce a close fit of 0„5 mm hole clearance. They are
specified where accuracy is paramount. - High Strength Friction Grip Bolts ~ also known as torque
bolts as they are tightened to a predetermined shank tension
by a torque controlled wrench. This procedure produces a
clamping force that transfers the connection by friction
between components and not by shear or bearing on the
bolts. These bolts are manufactured from high-yield steel. The
number of bolts used to make a connection is less than
otherwise required.
Refs.
BS 4190: ISO metric black hexagon bolts, screws and nuts.
Specification.
BS 3692: ISO metric precision hexagon bolts, screws and nuts.
Specification.
BS 4395 (2 parts): Specification for high strength friction grip bolts
and associated nuts and washers for structural engineering.
BS EN 14399 (8 parts): High strength structural bolting assemblies
for preloading.
Structural Steelwork--Bolted Connections