Pretension in Bolts 1

[MathMan]

Does anyone know what value of pretension is typically acheived by &quot;turn of nut&quot; method using 3/4&quot;ø A325 bolts?<br><br>I am designing a very lightly loaded clamped connection, and instead of specifying a value for the pre-tension, I would rather (if it is suitable) just note that the turn of nut method should be used.<br><br>The load per bolt is about 36kN (8kip).<br><br>

 

[jobeth]

This is a common question with no easy answer due to all the variations in friction coefficients and material properties. I suggest three turns of the nut. Check out <A HREF="

http://www.boltscience.com"

TARGET="_new">

http://www.boltscience.com</A>.

Hope this helps. Bill B. <p>William H. Bernhart, P.E.<br><a href=mailto: > </a><br><a href= > </a><br>I work as a development engineer for AMP - Tyco Electronics located near Harrisburg, PA. I help design interconnections and electrical connectors for aerospace applications.

 

[MarkRPflow]

See <A HREF="

http://www.steelstructures.com"

TARGET="_new">

http://www.steelstructures.com</A>

for the &quot;Structural Bolting Handbook&quot; - the best reference for &quot;Turn of the nut&quot; that I have found.<br><br>Pre-Installation Testing Required Tension (kips):<br>&nbsp;3/4&quot; A325 = 29 kip<br><br>Steel Structures Technology Center, Inc<br>42400 W. Nine Mile Road<br>Novi, MI&nbsp;&nbsp;48375-4132<br><br>Phone (248) 244-2910<br>fax (248) 344-2911

 

[TowerEngineer]

The &quot;Turn-of-the-Nut&quot; method, if properly executed, should provide a minimum pre-tension load of approximately 28 kips for a 3/4 inch diameter A325 bolt (reference AISC Table J3.7). The &quot;as-installed&quot; or actual bolt tension should be a bit higher than 28 kips. The theory behind the use of the turn-of-the-nut method is that the bolt will likely never fail if the bolt does not fail during installation.

The difficulty is always in the execution. The turn-of-the-nut method is an acceptable high-strength bolt installation procedure. Properly trained personnel should be able to use this method of bolt installation. It takes a fair amount of training under the supervision of experienced iron-workers to gain the experience necessary for the use of the turn-of-the-nut method.

It seems this response may be too late based on the date of your post, but this response was posted for future reference.

 

[dessie]

can anyone help me with info on Brinell hardness testing and help on calculations on 10mm ball using a 300kg load if the indentation was found to be 3.9mm

 

[indian325]

There is a general formula for converting the Brinell indention to hardness,


Hardness Brinell = Load / (Pi /2 x D x (D - Sqrt(D^2 - d^2)))

where Load is Kilograms
D = Ball diameter in mm
d = impression diameter in mm

Thus for your test, 10 mm ball and 300 kg load and 3.9 mm indentation,

HB = 300 / (3.142/2 x 10 x (10-sqrt(10^2-3.9^2)))

= 300/(15.71 x (10-9.208))

= 24 (a very low value for Brinell)

If you meant 3000 kg instead, the hardness would be

= 241 Brinell (roughly equivalent to RC 23 for steel)

Hope this helps.