Torque/ tightening force for NON-Preloded bolts (regular bolts) 2

[KubusKubus]

Hello all,

I would like to ask what is the Torque/ tightening force for NON-Preloded bolts (regular bolts). I have a standard tension connection. There is a lot of guidelines what is the torque value to achieve 75 % of yield load.
But I can't find what is the standard value of the torque (with particular friction coefficient) to tighten bolts as much to not get loose during work life.
Only value which if found is for bearing connection which is very ambiguous:

Tightening of the bolts: connected elements should be cling together. Tolerance less than 2 mm
is acceptable if this is not give in design recommendations. Bolts should be manual tightening
till “first point of resistance”. First point of resistance is defined as a tightening nominal hand
wrench with one hand power.

 

[Tmoose]

Not very much to go on here.

A single nut torqued to hold components within 2 mm of each other, with the bolt serving as part of a bearing connection, even in a completely static environment, sounds like trouble to me. Component springiness, thermal excursions, and probably other factors will come to play to loosen the nut. I think a self locking nut, jam nut, cotter pin, tab washer, etc is in order.

http://www.compbrake.com/wp-content/uploads/2012/12/CMB0992_93_94-CLEVIS-CLOTTER-PINS2-600x600.jpg

https://img.jpcycles.com/zoom/240-988_A.jpg

https://pitstopusa.com/images/F142791788.jpg

 

[MintJulep]

. Bolts should be manual tightening
till “first point of resistance”. First point of resistance is defined as a tightening nominal hand
wrench with one hand power.

Doesn't this answer your own question?

It's not a very good answer. But then it's not a very good question either.

 

[WinelandV]

KubusKubus,

If you're using structural high-strength bolts (A325, A490, etc), then, from a design perspective, you don't have any preload. Is this going to be completely true? No. But as you're finding out, it's very ill-defined what the pretension is.

Your bearing connection definition reads like what the RCSC has for structural bolting - a snug tight bolt for a shear connection (no tension). If you need pretension, then they give you a few options to get minimum preload:

Direct tension indicators (either snap off bolts or "squirter" washers
Skidmore method (fit up the connection, determine the torque needed for that set of bolts and plates)
Turn of the nut method (bring to snug tight condition, enforce the nut to rotate a set rotation beyond snug tight relative to the bolt)

If you're coming in after installation, then you may just need to pull the bolts, and get them installed correctly.

 

[drawoh]

KubusKubus,

Torque calculations are based on pre-load. For that matter, 75% of yield is based on pre-load. What are you trying to do?

--
JHG

 

[KubusKubus]

Thanks for the answers,


Well I designed standard tension connection. I got inquiry from the site - what torque should they use during tightening the bolts.
Surface of to be cling is hot deep galvanized steel plate. Bolts are 8.8 with washer.
From design point of view I do not require pretension. From serviceability point of view - some pretetion is required. So I'm looking for some table which would show what good practice of engineering says about tightening standard bolts.

 

[hydtools]

How tight do you, the designer, want the bolts?

Ted

 

[drawoh]

KubusKubus,

How much force do you want clamping those plates together?

--
JHG

 

[KubusKubus]

I don't require clamping force from design point of view. This connection is design as non- preloded bolts connection.
So the only torque which I require is for tightening the bolts as much as they won't get loose during working life.
So I would like to know if there are common sense recommendations treating about it.

 

[klaus.]

Eurocode gives recommendation on 'hand tide' bolt tightening

 

[KubusKubus]

Thank you very much, great answer. What is exact reference to this table - I cant find it in EN 1090-2 - only in DIN EN?
EN-1090-2 Chapter 8.3 Tightening of non-preloaded bolts - no table

 

[klaus.]

I am not sure if this table is given like that in the EN 1090
The table is from a presentation see page 30 (in german language)
Link

 

[sandman21]

To answer if snug tight is appropriate or not we would need to know more about what you are bolting and loading of the parts. If the member has machinery or live loads snug tight may not be enough to preventing loosening of the nut. If its a concern provide a jamb nut(double nut)connection or tack weld.

 

[KubusKubus]

Thank you Klaus, I wish to have this presentations in English.


This is the case:
Connection is a connection between anchor bolts and base plate of the canopy - please see on sketch.

 

[drawoh]

KubusKubus,

I am a mechanical designer. In my world, a bolt tightened somewhere close to its proof stress will not come loose. I understand that in architecture, sometimes bolts are deliberately left loose to allow thermal expansion and contraction. Perhaps you are clamping something that cannot withstand the full force of your bolt. In either case, you need some way to ensure the bolt or nut will not rotate out. Your torque strategy will be based on what you are trying to do.

--
JHG

 

[klaus.]

Kubus
in structural engineering (architectural) there is a thing called prestressed bolts
The bolts are tightened to a high level in order to make the connection 'stiff'

Most of the other bolts are not prestressed bolts
So the question is....how much to tighten this not prestressed bolts

 

[drawoh]

klaus,

There must be some reason why you do not tighten the bolts. There must some some force requirement or configuration requirement. If we do not understand this, we cannot suggest a strategy for turning down bolts.

--
JHG

 

[WinelandV]

Going back to the original post:

I would like to ask what is the Torque/ tightening force for NON-Preloded bolts (regular bolts). I have a standard tension connection.

The big issue is, if this is a connection in which there is tension in the bolts, from a structural bolting perspective, the bolts need to be preloaded.

Now then, the structure, is this a cantilevered canopy? Or is there a mirrored half that didn't make the image shown? If the first, you're going to have moments that need to be resisted at the base. If the second, you're still going to have uplift from the roof during a wind event. Either way, your bolts will be loaded in tension, and you should be preloading them. The amount of preload is dependent on bolt diameter. The amount of torque to hit preload is dependent on the specific bolts and plates being used. In the U.S., we don't get to estimate the torque req'd. You either calibrate for the specific situation (i.e. using a skidmore device), or you use the turn of the nut method to ensure proper preload.

 

[KubusKubus]

Yes, I have never got question regarding torque. That's why my concern is. The situation is as you described - moment connection with bolts mainly in tension caused by :
- cantilever Dead Load
- wind load, which can reverse tension in bolts.

Could you please guide me if in this case should I use pretension torque value instead of snug-tighten torque value?
Equals to pretension force 0.7* Pty = Tb. With torque value eqauls to 115 Nm - the pretension force is equal to
0.2*Pty


The issue is that prelodaing bolts requires special procedure, carefulness. I can't control it from the office. That's why reserved value of the torque.

 

[klaus.]

There must be some reason why you do not tighten the bolts.

Well in structural engineering there are 2 things
1 ) bolt tightening
and
2 ) bolt prestressing

basically from code and design these are 2 different things

of course each bolt need to be tightened ...but not each bolt need to be prestressed

Prestressed connections are more expensive than 'normal' connections....and money rules the world