Pretension in Bolts
Pretension in Bolts
(OP)
Does anyone know what value of pretension is typically acheived by "turn of nut" method using 3/4"ø A325 bolts?
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.
The load per bolt is about 36kN (8kip).
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.
The load per bolt is about 36kN (8kip).





RE: Pretension in Bolts
William H. Bernhart, P.E.
I work as a development engineer for AMP - Tyco Electronics located near Harrisburg, PA. I help design interconnections and electrical connectors for aerospace applications.
RE: Pretension in Bolts
Pre-Installation Testing Required Tension (kips):
3/4" A325 = 29 kip
Steel Structures Technology Center, Inc
42400 W. Nine Mile Road
Novi, MI 48375-4132
Phone (248) 244-2910
fax (248) 344-2911
RE: Pretension in Bolts
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.
RE: Pretension in Bolts
RE: Pretension in Bolts
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.