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Tightening Procedures in Steel Structures


Structural Bolts:

Two commonly used types of bolts are:

  1. Unfinished(A307).
    1. High strength bolt(A325,A449,A490).
    2. A307 is known by names unfinished, rough, common, ordinary and machine.
  2. They are made of low carbon steel having tensile strength of 60Ksi.
  3. A325 is made of medium carbon steel whose tensile strength decreases with increase in dia
  4. High strength bolts can be tightened to large tensions.

Tightening procedures:

Research Council on Structural Connections (RCSC) prescribes four tightening procedures.

  1. Turn of the nut method
  2. Calibrated-wrench tightening
  3. Installation of alternate design bolts
  4. Direct-tension-indicator tightening
  5. In riveted connections magnitude of clamping is function of length of rivet and magnitude of shrinkage after the head is formed.
  6. Magnitude f slip depends on the extent to which rivet fills the hole.

Bolted & Riveted Connections

Behavior of Mechanically Connected Joints

Bolt Connections

Types of Connections

Slip-Critical connections:

  1. Connection transmits the force by friction produced between the faying surfaces by the clamping action f the bolts.
  2. Slip-critical connections are recommended for joints subjected to stress reversal, severe stress fluctuation, impact, vibration or where slip is objectionable

Bearing type connections:

  1. Load is transferred by shearing and bearing on the bolt.
  2. Capacity in shear depends on whether shear plane intersects the body of bolt or threaded portion.
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