Calibrated Torque Method 1

[tmgczb]

How to calculate the Torque Values according to pretension of high strength bolts？
For example，high strength bolts，A325, M20, required pretention is 140kN, what is the Torque to be provided?

 

[rowingengineer]

https://www.google.com/url?sa=t&sou...4QFnoECAMQAQ&usg=AOvVaw2cwkDtWqF3__tsH4GT4bkg

 

[rowingengineer]

The linked manual is my favourite bolt resource

 

[tmgczb]

This handbook is very good. But vendor data is not code or standard.

 

[centondollar]

Codes and standards do not provide all the information you need to engineer something - that´s what textbooks, worked examples, reference projects and education are for. I highly doubt that you will find tables for required torque of pre-tensioned bolts in a standard.

 

[tmgczb]

Yes, some standards avoid this topic. Do you have any books containing this information? Kindly please share.

 

[3DDave]

There are literally dozens of websites that describe how to calculate tension caused by torque.

Most of them say the same thing - perform a test. Because slight changes in friction in the threads or against the turning nut or bolt will change the amount of torque to create whatever amount of tension you want.

It never seems to occur to some people that if what they are looking for isn't readily found yet the topic is of wide interest that maybe the reason is because there isn't a way to reliably produce that information. If it could be standardized it would have been standardized.

So - locate a bolt tension tester and try your bolts with it.

https://www.vfbolts.com/product/clarkester-tester/

for example.

 

[SnTMan]

Strange usage of quotes...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[HTURKAK]

For calibrated-torgue method , ( a calibrated wrench is used ) , it must be calibrated with tests and should be
tested periodically using a calibrating device that gives the bolt tension directly ..

A very good source on this subject is the Structural Bolting Handbook.

https://steelstructures.com/publications/structural-bolting-handbook-2016/

When you write ( Torque Values according to pretension high strength bolts，A325, M20 ) and searh the web,
two of the outcomes ;

https://www.portlandbolt.com/technical/bolt-torque-chart/#bolt-torque-a325

https://www.norbar.com/Portals/0/downloads/TorqueValueGuide.pdf

 

[tmgczb]

Is the first book available or not？

 

[tmgczb]

How should I improve？

 

[rb1957]

yes, use of quotes is "unique".

two ways to do quotes ...
1) olde school ... copy and paste the text you want to quote, and put ""s around it.

2) use the quote icon but I don't know how you're using it to get the effect you are showing ... you're trying to copy some text from a previous post, but inserting your response instead ??

Strange usage of quotes..

ok, copy and paste the text you want to quote, then highlight and click the quote icon, then it asks "who?" and type the poster's name "SnTMan" then when you preview you see the quote.

another day in paradise, or is paradise one day closer ?

 

[phamENG]

SnTMan/rb1957: OP doesn't think he's quoting anyone. This forum doesn't have an option to reply directly to somebody else's post (like a reddit or LinkedIn comment board), so a few people use the quote button because they can't seem to cope with the idea of simply stating somebody's name at the beginning of a post.

tmgczb: the quote button is for just that. Quoting somebody's words to reference a specific part of their post or give them credit for it when you restate it. As rb said, that button is just a 1990's fancy way of "quoting" somebody.

Regarding the question about bolting: does it matter what standards you're using? Research Council on Structural Connections has the RCSC Specification for Structural Joints Using High-Strength Bolts. I'd advise you read through that. One bit of useful information:

Calibrated Wrench Pretensioning: The pre-installation verification procedures specified in Section 7 shall be performed daily for the calibration of the installation wrench. Torque values determined from tables or from equations that claim to relate torque to pretension without verification shall not be used.

So just looking for a table isn't going to help you.

 

[rb1957]

perhaps a different tack ?

@tmcczb ... what didn't you get from the 1st post ? I know there's some "VDI" document (2230?) out there that goes into preload in a big way.

another day in paradise, or is paradise one day closer ?

 

[dik]

The Portland Bolt link shows the problem with calibrated wrenches in the scatter between the minimum and maximum torque values. Therein lies the 'rub'. Nearly always use turn of nut...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[rb1957]

there are many ways to control the preload applied, with differing levels of accuracy ...

uncontrolled (man with wrench),
using a torque wrench,
using "turn of nut",
using PLI (Preload Indicating) washers,
etc.

but the OP questioned "how to calculate ..." ... asking for calculation methods, no?

another day in paradise, or is paradise one day closer ?

 

[phamENG]

but the OP questioned "how to calculate ..." ... asking for calculation methods, no?

Yes. And I think we've done a pretty thorough job of showing you can't calculate it. At least not with enough accuracy to make the exercise worthwhile. Sure, you could come up with some sort of first principles approach looking at the threads as an inclined plane and do a basic vector analysis to determine the required torque to apply a force along the axis of the bolt. But you'd have to assume friction coefficients that are unlikely to be accurate in the real world, modify it for manufacturing tolerances, etc. Which is why every reputable resource/standard tells you not to trust such calculations.

 

[WinelandV]

rb, we don't calculate the torque req'd for pre-tensioning high strength bolts. At least not with equations. Hence all the directing to calibrated torque wrenches (and all the procedures related to using one of those), and dik's mention of using turn-of-the-nut method.

We can, however, calculate the bolt stretch required to attain the amount of pre-tensioning needed.

 

[rb1957]

"we don't calculate the torque req'd for pre-tensioning high strength bolts" ? really ?? how do you specify torque required ?

sure, you can say "rules of thumb", torque to 70%, maybe some value in a table somewhere.

surely you calculate the preload required; and the torque to achieve this ?

another day in paradise, or is paradise one day closer ?

 

[phamENG]

Nope. We calculate the preload required, and then specify a procedure to get there. Usually it's one of those mentioned above. Calculated torque wrench can be a good one, but not the only one. They sample several bolts (have to make sure you don't pick the cleanest or the dirtiest of the batch) and put them in a Skidmore machine. Start tightening it until it reaches the desired preload, record the torque. Repeat for the necessary sample size. Now you know what torque you need. Go install bolts. If you stop for lunch, drop the wrench, reach a set number of bolts installed, or other triggers, you go back and repeat the test to verify the torque value.

If you use compressible DTI washers (direct tension indicators), you don't need the torque wrench. You do the Skidmore test and measure the gap in the washer. Then you go install the bolts and use a feeler gauge to confirm that the DTIs have been compressed at least that far.