Aluminium Design and Construction John Dwight

Figure 3.2 Thread insert.
a coil-spring, made of rhomboid section stainless steel wire, which can
be screwed into the hole. It greatly increases the life of the thread if the
joint has to be unscrewed from time to time.
3.2.2 Friction-grip bolting
This type of connection is employed when maximum rigidity is needed
under shear loading. It calls for the use of special high tensile (HSFG)
steel bolts in clearance holes, these being torqued up to a high tension
so that the service loading is carried entirely by friction. The technique
is less advantageous than in steel (Section 11.2), but it still has some
application. Practice broadly follows that for steel structures.
The bolts should be of general grade (BS.4395: Part 1). HSFG bolts of
higher grade are held to be unsuitable for aluminium, and BS.8118
restricts even the general grade to use with aluminium having a proof
stress over 230 N/mm2 .
It is important that the mating surfaces should be flat, clean, free of
defects, and also free from any substance that would reduce the
development of friction, such as paint. Preferably, the surfaces should
be grit-blasted. British Standard BS.8118 recommends a standard treatment,
and when this is used a stated design value may be taken for the slipfactor
(Section 11.2.6).
Tightening procedures are as for joints in steel, either by controlled
torque using a calibrated wrench, or else using the part-turn method.
Refer to BS.4604.
3.2.3 Riveting
In light-gauge construction, the decision whether to rivet or weld is
slanted less towards welding than it is in steel. Small aluminium rivets
are widely used in some industries, either of conventional solid form or
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