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Tips on Bolt Tensioning


Calculation notes on using Hydraulic bolt tensioning tools.

Formula to use:
Residual Bolt Load = Bolt Stress x Bolt Tensile Stress Area
Units:
Residual Bolt Load = (N or Tons)
Bolt Tensile Stress Area = (mm2 or In2)

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Below are tables of standard ISO Metric and Imperial Thread forms along with applicable tensile stress area’s.
Step1: Determining required bolt load from a known bolt stress.

Caution:
Using these Tensile Stress Area values is only applicable for fully threaded studs, if the stud in question is wasted or reduced in diameter, the Tensile Stress Area will need to be calculated using the smallest stressed diameter on the bolt.

Formula to use:
Bolt Tensile Stress Area = pi/4 x (d2)
Units
Bolt Tensile Stress Area = (mm2 or In2)
d = Smallest Stressed Diameter on bolt = (mm or In)

Design Check:
It is always good practise to determine the % of bolt yield you are applying, if the final bolt stress exceeds 75% of the bolt yield strength, then it may be neccasary to consider the fatigue characteristics of the bolt and joint.

NEVER EXCEED 95% OF THE BOLT YIELD STRENGH

Formula to use:
% of Yield = (Bolt Stress Required / Yield Strength of bolt ) x 100
Units:
Bolt Stress Required =(N/mm2 or Ton/In2)
Yield Strength of Bolt =(N/mm2 or Ton/In2)


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Provided by:

Tentec Limited
Plymouth House
Guns Lane
West Bromwich. West Midlands
United Kingdom. B70 9HS
Internet: www.tentec.net
Email:sales@tentec.net
Telephone: +44(0)121 524 1990
Telefax: +44(0)121 525 1999

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