STEEL - Materials for Civil and Construction Engineers - page 107

3.6

Fastening Products

Fastening products include (Carter, 2004)

Conventional bolts

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Twist-off-type tension control bolt assemblies

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Nuts

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Washers

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Compressible-washer-type direct tension indicators

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Anchor rods

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Threaded rods

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Forged steel structural hardware

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Table 3.7 summarizes the applicable ASTM specifications for each type
of fastener (Carter, 2004). High-strength bolts have a tensile strength in ex-
cess of 100,000 psi. Common bolts have a tensile strength of 60,000 psi. The
preferred material for anchor rods, F1554 Grade 36, has a yield stress of
36,000 psi and an ultimate strength in the range of 58,000 to 80,000 psi. A36,
with a yield stress of 36,000 psi, is preferred for threaded rods. Nuts, wash-
ers, and direct tension indicators are made with materials that do not have
a minimum required strength.
Structural connections are made by riveting, bolting, or welding. Rivet
connections were used extensively in the past, but modern bolt technology
has made riveting obsolete. Bolted connections may be snug tightened, pre-
tensioned, or slip critical (Miller, 2001). Snug-tightened joints are accom-
plished by either a few impacts of an impact wrench or the full effort of an
ironworker using an ordinary spud wrench to bring the members into firm
contact. Pretensioned joints require tightening the bolt to a significant ten-
sile stress with a corresponding compressive stress in the attached members.
Four methods are used to ensure that the bolt is tightened to a sufficient
stress level: turn-of-nut, calibrated wrench, twist-off-type tension-control
bolts, and direct tension indicators. Bolts in slip-critical joints are also in-
stalled to pretensioned requirements, but these joints have “faying surfaces
that have been prepared to provide a calculable resistance against slip.”
When the joint is placed under load, the stresses may be transmitted through
the joint by the friction between the members. However, if slip occurs, the
bolts will be placed in shear, in addition to the tension stresses from the
installation—hence the need for high-strength bolts.

3.7

Reinforcing Steel

Since concrete has negligible tensile strength, structural concrete members
subjected to tensile and flexural stresses must be reinforced. Either con-
ventional or prestressed reinforcing can be used, depending on the design