cr4 - thread_ bolt length

7/28/2019 CR4 - Thread_ Bolt Length

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AnonymousPoster

Bolt Length01/05/2010 9:04 AM

I had adiscussion with one of my friend regarding the bolt length , and the

discussion was about the extra threaded part of the bolt that will be

exposed after the nut , what is the importance or the need for the extra

threaded length of the bolts after tightning the nut ? is it to facilitate the

installation ?

I assumed that we are connecteing two flanges together using a machine

bolts and nuts from the other side , normally the length of the bolt is

specified to be more than the length of the fittings , two flanges + 1 nut +

1 washer , so what is the need for this external exposed threaded length

after the nut ????

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#4 "Re: Bolt Length" by TVP45 on 01/05/2010 10:35 AM (score 2)

#5 "Re: Bolt Length" by BoltIntegrity on 01/05/2010 11:50 AM (score 2)


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#13 "Re: Bolt Length" by Trevor Walden on 01/06/2010 4:47 AM (score 1)

#14 "Re: Bolt Length" by Randall on 01/06/2010 5:55 AM (score 1)

#19 "Re: Bolt Length" by Hooker on 01/06/2010 9:21 AM (score 1)

#26 "Re: Bolt Length" by redfred on 01/06/2010 11:23 AM (score 1)


#36 "Re: Bolt Length" by nick name on 01/07/2010 4:20 AM (score 1)


redfredGuru

Join Date: Dec 2008Location: Long Island NYPosts: 4473Good Answers: 299

Re: Bolt Length01/05/2010 9:34 AM

One of you is only thinking of the static assembled configuration. The one

who believes this aids assembly, I think is correct.

During assembly there will be a gap between your two flanges. So during

assembly when initially connecting the flanged assembly the first bolt, nut,

and all washers will be asked to briefly hold all of the components together

with this added gap between the flanges. During this brief period, you

should have as many threads of the nut as possible in contac t with the

bolt to handle the loads that will occur during alignment and inclusion of

the remaining hardware.


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#4

#5

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AnonymousPoster


In some cases I think it is just a way of dealing with the issue of "is the

bolt too short"? I have heard 1.5 threads exposed and others have told me

3 threads exposed. This was in equipment where the hardware was holdingthe electronics enclosure together. The extra threads served nothing

beyond making the workmanship inspectable.

nick nameGuru

Join Date: Mar 2007Location: City of LightPosts: 2868Good Answers: 107


Not only, nut and bolt have chamfers so that if the bolt would have only

the length to be flush with the nut surface at least one thread would be

not engaged so that the loading capability in shear would be less

required. From an other point of view this over length considers all

possible deviations in the thickness of components so that in the worsecase all nut threads will be engaged.

TVP45Guru

Join Date: Jul 2007Posts: 4372Good Answers: 138


There is a standard of 3 exposed threads. This is a "rule of thumb" but

serves two purposes:

1. It makes the assembly easy to inspect;

2. The first thread or so is not full and cannot be counted on.

Now, Shigley and Mischke in their mechanical design handbook make the

argument that a good bolted joint only requires about three full threads. I

believe them, but I still like belt and suspenders.

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BoltIntegrityPower-User


Three threads, two or one protruding beyond the nut of a fully tightened

joint make no difference. Anything beyond the nut is superfluous. In

fact, it can be argued that the last threads in the nutreally don't do much

either since it's the first few threads that take most of the load.

2

2


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#11In reply to #10

#12In reply to #11

Join Date: Aug 2008Location: EuropePosts: 231Good Answers: 20

Practically, the presence of extended threads simply provides a visual

guarantee that there is at least minimum thread engagement.

On the other hand, sometimes there is a real requirement for much more

than even three threads. In fact, these cases require the equivalent of

one diameter

protruding

beyond the

nut. As you

can see in theadjoining

picture, these

are large

fastener

applications

which are

tightened by

the use ofbolt

tensioners

rather than by

typical

wrenches. Bolttensioners are

used when

speed of joint assembly and precise control of bolt load are required.

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AnonymousPoster


it can be argued that the last threads in the nut really don't do much

either since it's the first few threads that take most of the load.

Explain that in terms of an unbroken inclined plain

RandallGuru

Join Date: Aug 2005Location: HemelHempstead, UKPosts: 2602Good Answers: 106


Bolts stretch.

I wonder if there is an argument for a slightly variable (pre-tightened)

pitch for units in very precise assemblies?

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bwireGuru


Bolts stretch doesn't explain the first three threads taking more load

than the others.


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#14

In reply to #12

#20In reply to #14

Join Date: Dec 2007Location: Upper Mid-westUSAPosts: 7506Good Answers: 96

I think the variable pre-tightened concept is covered by the various

classes of thread.

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RandallGuru

Join Date: Aug 2005Location: HemelHempstead, UKPosts: 2602Good Answers: 106


The tension in the bolt at A is constant; is decreasing through B

towards zero at C.

Therefore the slope of the thread in the bolt is steeper at A

decreasing through B to C.

The effect in the nut is the opposite but not as pronounced and not

shown here.

I hope you can just see that the slope of the thread in both nut andbolt is parallel in the upper section, but curves so that it is steeper

in the bolt in the lower section.

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DedalusAssociate

Join Date: Aug 2009Location: ChinaPosts: 25


Dear Randal,

As a retention feature this has merits (such as tri-lobial bolts or

uneven pitch bolts).

My concern with all these retention features however is that they

tend to increase friction significantly, reducing even further the

energy available for clamp-force. Then you need to increase the

bolt material grade, then the cost goes up. Also, it is virtually

impossible to calculate and predict the behaviour of such joints, so

joint development relies exclusively on physical testing which is


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#37

In reply to #20

#32In reply to #14

also expensive and time-consuming.

bwireGuru


Re: Bolt Length01/06/2010 5:26 PM

Good points, the number of time I've encounter the philosophy

that tight threads equal a preferred engagement eludes me.

Cheater bars aren't needed to thread a nut onto a bolt

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nick nameGuru



You have a wrong view angle of the needs for such anti loosening

features.

Without them the bolt/nut pair is hold in place only by the

preloading generated friction which has to be bigger than the

active moment generated by preloading and thread angle. If for

any reason the preload decreases then holding capacity

decreases , it is an unstable process.

The different approaches (trilobs or similar) have the advantage

that the friction forces which hold the bolt/nut together are NOT

any more depending on the preload magnitude !

Of course friction is higher and torque has to be increased

according to the higher losses at tightening but this is via tests

possible to define and adjust.

With respect to material quality the trend to miniaturisation leads

anyway to smaller bolts and the stronger material allows a higher

ration L/d which is better for fatigue. Since Young modulus is the

same independent of elastic limit, for same load, a high strength

bolt will be more elastic and reduce the variation of bolt forces

under load thus being more resistant to fatigue.


RandallRe: Bolt Length

01/07/2010 9:31 AM

bwireGuru

Join Date: Dec 2007Location: Upper Mid-west


Thank you for taking time for this and yes I understand the point

you're making but it seems odd especially in this day when even

wood screws are having rolled thread that the threaded portion of

bolt encapsulated within the nut should be deemed of less integrity

than the remainder/shoulder or unthreaded length of the bolt.

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bwireGuru



I ran out of time to add

I would expect stretch between A and B to reflect the stretchbetween B and the bolt head

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Randall Re: Bolt Length01/07/2010 9:35 AM

crimich13Re: Bolt Length02/26/2010 6:30 PM


omw7Power-User

Join Date: Apr 2007Posts: 237Good Answers: 14


I strongly disagree with this. In the circumferential direction the bolt is in

compression and the nut is in tension. When the bolt is just as long as

the nut, some of that compression deforms the end of the bolt and

makes it get smaller in diameter. The thread engagement is reduced. Iunderstood that this is the reason for having threads protruding from the

end of the nut from a calculation point of view.

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omw7

nick nameGuru



The radial forces are the same for bolt and nut. But the radial stiffness

of bolt is a lot higher than the nut stiffness so that the major

deformation will be the nut one and this leads to an increase of mean

diameter of the nut and a reduction of the shear area.

This is the basis for the ratio between nut hexagon and bolt diameter:

the nut has to be stiff enough in order to limit this radial deformation

which penalizes the carrying capacity.

If for any reason you should use nuts made from a material having a

young modulus smaller than the bolt the hexagon has to be increased

to compensate the higher radial deformability.


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omw7Power-User



However, when the bolt is cut short (say flush with the nut) then the

end of the bolt will dimple under the compression forces which in turn

reduces its external radius and so the engagement of threads with the

nut (which itself has expanded and so also reduced its engagment).

So the final capacity is not as per the calculated value.

Effectively, the different codes that I have managed to find that

reference the number of additional threads beyond the nut have a

varied view on the number of threads between 1.5 to 3.

Of course this is all to do with bolts in tension and not shear.

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omw7

nick nameGuru



A couple of remarks:

1- the load is transmitted by 3 threads at the OPPOSITE of the

bolt free end!

2- the nut diameter increase and the shear force reduction CAN be

calculated thus it is possible to know from the start how much the

bolt will hold in tension!

3- the standard nut dimensions (as mentioned) were defined so that

their radial stiffness will be big enough to avoid such portance

losses. Never the less the bolt stiffness is SOO big in comparison

with the nut that its own compression can be TOTALLY neglected.

So that from the beginning the probable load carrying capacity

I have several FEA results I can send you, I have not any more the

original jpg files (are embbeded in power point and word files and I

do not know how to record them again as pictures and integrate to

a message on CR4) so that I can send only if you give an email

address but not here only on the private channel.


nick name Re: Bolt Length03/01/2010 12:10 PM

nick nameGuru



8/26


Thanks to recommendation I recovered the pictures as JPG file and

can display them.

The results come from different FEA with different software and

threads done under different contact conditions, but all of them are

consistent in following directions:

- Load is transmitted by the first threads

- End threads are NOT for load transmission but for all other

mentioned reasons or at least for some of them.

- Nut radial expansion (which visible on the 2 pictures at top) is very

small and the bolt has almost no radial deformation.

- The loading can be from start correctly estimated.

The picture top-right shows also how the nut thread is deformed

under load (the small red circles indicate the region where the nut is

supported by the parts considered as st iff).

It is also interesting how the bolt is loaded and how the stress


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#69In reply to #68

#6

#7

expands within it.

The bottom picture shows also how every bolt thread root is a

stress concentrator.

If from a qualitative point of view all comments are valid it is

different if the quantitat ive aspect is considered.

Hope it will make some aspects clear.

Thanks again for the software indication it can be a real help.

Nick Name

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omw7Power-User



Great pictures. Thanks for posting them.

I guess that this is a standard height coarse thread with about

about 5 threads. Even with a reduced height lock-nut we wouldstill have 4 threads.

I'm happy to see that the bolt does dimple slightly at the top. This

had been reported to me by a nut-bolt specialist and it is good to

see the confirmation from your pictures.

So if the bolt head was flush with the nut, the other remaining

engaged threads would have a higher load ? I imagine that for a

standard height bolt with 5 threads, this would be reduced to 4

threads (more or less).

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omw7

ozzbGuru

Join Date: Mar 2007Location: Rosedale,Maryland USAPosts: 3043Good Answers: 125


There is no need for it though it may help in assembly. Bolts though are

manufactured in standard lengths. Better to chose one that has a few

threads sticking out then one that you can't get a full nut on. Failure to

have all the threads in the nut when torque it down may cause the

threads to fail usually on the bolt but have seen them pull out of the nut.

To obtain the nut flush with the end of the bolt means you would have to

start your tightening before you had a nut full of threads.

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AnonymousPoster


Thanks for all your replies and Best Regards ,


10/26

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#13

#31In reply to #13

Anthony@ALNOCommentator

Join Date: May 2009Location: Gosford,

Sydney, AustraliaPosts: 58


Hello Guest,

What a great question

The extra length is generally an allowance as bolt lenghts come in 5mm or

10mm increments pending on the dia. it may be 25mm increments

therefore a bolt lenght would be rounded up to the nearest length in theideal world. In many cases to exert clamping pressure you may only need

one thread but this would be dependant on the dia. and clamp pressure

required.

hope this helps

Anthony@alno

http://www.alnoproductservices.com.au

Anonymous

Poster

Re: Bolt Length

01/05/2010 11:45 PM

The following reasonings are offered from my end : -

1. Bolt length should always be more than the measured length of parts to

be assembled because many a time the parts being loose or difficult to

access, shall require pre-holding of parts on bolt length so that bole end is

available clearly for engaging nut.

2. Actually bolt length required is = measured length of parts + one nut

width and any extra length does not serve any useful purpose. Infact

extra projection shall be an obstruction while dismantling at a later stage

due to corrosion , dust particles sticking and jamming the clearance

between bolt & nut threads. Use of end caps are advised in this regard.

3. Sometimes exact required bolt length may not be available and instead

of cutting and using, it is better to use bolt of nearest length available.

Trevor WaldenActive C ontributor

Join Date: Nov 2009Posts: 19


ANSI piping was designed for outdoor Oil Industry piping. The bolts had to

do the same service. But contractors try to cut costs so bolting standards

were included as part of the Piping Specification. For maintenance

purposes it was required that bolts not be too long, the exposed threadwould rust. And also long enough for Assembly, allowing for gasket

compression. The requirement was settled by half the diameter of bolt

maximum, and the bolt end to show. Single plain washers were standard

under bolt head and nut. Lock Nuts (thinner than full nuts) were required

where vibration from machinery would affect the piping.


bwire Re: Bolt Length01/06/2010 4:31 PM


11/26


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#16

#34In reply to #16

Location: Reading,Berkshire, UK. Goingunder cover.Posts: 8914Good Answers: 257

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DedalusAssociate



The thread at the start of a bolt is usually incomplete, i.e. it does not

meet the geometric requirements for an ISO thread and cannot be used to

take torque.

This is because of the method of manufacturing threads which leaves a

short length incomplete, and is made worse by normal piece-to-piece

variation.

Therefore, it is usually recommended that bolts are chosen to slightly

protrude at the back of the nut so as to ensure that the incomplete

portion of the thread is not engaged in the nut. The recommended

protrusion in my company is at least 1.5x thread pitch. In practice of

course we do not design every bolt from scratch, we select a bolt from a

list of standard sizes. Therefore sometimes the only available size happensto be even longer than 1.5 threads more than the clamped piece, and so

you see some joints where the bolt protrudes a lot at the back.

In addition to this, you may find bolts which have a short, unthreaded,

cylindrical portion attached at the tip and this make the bolt stick out

even more. This is called a "pilot point" or I think "dog point" in the US. It

is there to guide the bolt into the nut and prevent cross-threading during

fast assembly

bolt drawing

Hope this helps

AnonymousPoster


The people that answered this have some good opinions and a good set of

handy guidelines. There is no use for extra threads unless you may want

the option to put on a "jam" nut or safety wire. The exposed thraeds are

sometimes sharp enough to pose a safety risk in which case you would opt

for an acorn nut or plastic cap. If extra threads aren't used for drawing

components together. Design the bolt/assembled unit without them.

Loctite makes good products for securing theaded items.

bwireGuru

Join Date: Dec 2007Location: Upper Mid-west


Good assembly techniques include removal of sharp edges to avoid safety

hazards...

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#18

#21In reply to #18

USAPosts: 7506Good Answers: 96

CaptMoosieGuru

Join Date: May 2009Location: Red Hook, NewYork (Mid-Hudson RiverValley)Posts: 1945Good Answers: 65


Other than using the bolt projection as a visual inspection method, as a

safety precaution, I'd rather have extra bolt thread projection especially

where there are vibrations or load cycles present in a structure orassembly. No matter how hard we try to torque the little buggers down

they always loosen up!

Making my 2 Cents known! Hmmmmm I wonder how magnificent a

Moose quarter would look like if the US Treasury ever gets around to

making 'em!!! LOL Anyone interested in signing my petition????

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DedalusAssociate



Dear Guest,

What holds the joint together is CLAMP FORCE, not FRICTION. Clamp force

comes from bolt extension. This comes from torque on the bolt head

against the thread gripping the nut side. There is probably some

theoretical merit in the previous comments about only a few threads

actually taking the majority of the load, however when designing a new

joint for mass production you need to design it in such a way as to

achieve the full required thread engagement or else you may have some

threads stripping under the torque or others coming lose in operation.

The correct design thread engagement varies from joint to joint and does

need good calculation and/or testing (e.g., torque-angle or torque-clamp

force testing) before it can be decided. As a rule of thumb start with 1.5

bolt diameters for bolt into steel pieces or nuts and 2 bolt diameters for

aluminium.

PS1.: Loctite may be a good solution for one-off fixes on my classic car

but is not going to hold joints together in production. At best it may

prevent a bolt from coming off after it has already gone lose, i.e. the joint

already failed.

PS2: On a typical joint, friction takes up about 80%-90% of the energyyou put in through torque! So only about 10-20% of your torque is left to

extend the bolt and create clamp load. Do not waste this energy further

by bad joint design. Follow the rules, there is good reason for them.



Just a bit of clarification: Clamp force does NOT come from bolt

2


14/26

#23In reply to #18

#19


extension; It's a result of bolt elongation. I'm sure that this is what the

author had meant but, since this post concerns bolt "extension", I

thought it important to point out.

However, there is another more serious clarification that needs to be

made: Clamp load does NOT come from "torque on the bolt head..." (or

nut). For example, if the bolt head (or nut) was welded onto the flange

(literally or f iguratively ie galling) and turning force was applied, the

"proper"(!) torque would eventually be achieved but the bolt will not have

stretched. Here's a real-life example that makes this clear.

"Torque" in terms of bolting is very critical yet still widely misunderstood.

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nick nameGuru



"What holds the joint together is CLAMP FORCE, not FRICTION."

The clamping force without friction will not maintain the bolt/nut in place

!

There are 2 aspects:

- holding together the parts against transverse forces the c lamping

force has to be so big that the friction force it generates on the

potential sliding surface will be more important than the transverse

maximal force. This is the reason this force has to be maintained all time

long and which ever will be the loading of the pair.

- holding together the pair bolt/nut this is more difficult since anyeven minute sliding on the thread surface will get the bolt/nut loose.

Axial forces having a neglectable effec t on it. This is the reason the

machines used to check the performance of an anti moose principle are

based on a transverse sliding system. Here again the combination

between axial force (clamping) and friction on the thread contact

surfaces will keep the pair together or not. For THIS is a bonder as

LOCTITE or similar is good since it maintains the threads after preloading

together and does not allow a loss of preload.

It is a bit more complex than it appears at first look.

HookerGuru

Join Date: Mar 2008Location: Bridgewater,Va.Posts: 1057


Lots of good answers here.

The standard in aviation is minimum 1.5 threads through the nut. You'll

hear lots of design reasons for this but I can say from experience that

anybody that has to do pre-flight or post-flight inspections really

appreciates the excess.

From my experience in helicopters it is really nice to be able to glance at

an area and quickly visually verify that everything is in place. If a bolt did


15/26

#22In reply to #19

#24In reply to #22

#26In reply to #24

Good Answers: 46 not significantly protrude through a nut the inspection process would be

much more tedious.

Also, on an assembly where a nut is not visible it is nice to be able to run

a finger behind and verify everything is intact. If I couldn't feel the bolt

protrusion, that would prod me into a closer inspection of the area.

Hooker



Join Date: Aug 2008

Location: EuropePosts: 231Good Answers: 20


Hooker,

It's good that you point out the importance of inspection. Indeed,

physical inspection is a great way to

ensure that the bolts are still there. The

next most important issue is, "is the bolt

still tight enough".

To address this, special bolts areavailable which have an optical sensor

that changes colour based on the degree

of clamp load. In this example, if a bolt

has loosened, the sensor shows red.

When re-tightened to the proper load

(irrespectiveof torque) the sensor

becomes black again.

Proper elongation measurement is a more definitive way of measuring

clamp load but, as a simple "go, no-go" indication, this technology seems

to be quite interesting.

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HookerGuru

Join Date: Mar 2008Location: Bridgewater,Va.Posts: 1057Good Answers: 46


Wow, love those optical bolts. I can think of a couple of helicopter

accidents where having those in critical systems may have prevented

the mishaps.

"When re-tightened to the proper load (irrespectiveof torque) the

sensor becomes black again."

So, if not by torque, how is the bolt installed to the proper clamp load?

I'm sure I'm probably missing something outlandishly simple here.

Hooker

redfredGuru


Think about what happens with a bolt that binds from galling or debris


16/26

#28In reply to #26

#29In reply to #26

#61In reply to #26


in the thread. You can bring the wrench up to the specified torque

but not have the bolt's head touching the flange.

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HookerGuru



Agreed, to a point.

If I ever found a licensed mechanic that allowed that to happen on

an aircraft, I'd make sure his license was pulled and that he'd never

work in the field again.

There is no excuse for that to happen, and even if inadvertent,

would "probably" be caught by the inspector at sign-off. Unless, of

course, there was corrupt maintenance management shortcutting

the practices and processes.

I am speaking exclusively of the aviation field.

Hooker



Re: Bolt Length

01/06/2010 11:39 AM

Exactly. Even if the bolt's head does touch the flange, variations in

friction factors arising from lack of lubricant, excess lubricant,

lubrication contamination, dirt in the threads, damaged spotfaces,

washer inconsistencies, thread damage (and on and on and on....)

the "proper" torque will likely not produce the desired (required!)

clamp load.

Interestingly, torque wrenches are usually required to be calibrated

to +- 2%, or so. This is absolutely useless when the use of these

"calibrated" torque wrenches can still result in preload variations of

+- 20, 30, 60, 80 or even over 100%!

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crimich13Power-User


So load would be the clamping force under the head?


17/26

#27In reply to #24

#30In reply to #27

#25

Join Date: Mar 2009Location: Manchester NHPosts: 119Good Answers: 4




Hello Hooker,

I'm sorry for the confusion. Indeed, the bolt is tightenedby "torquing".

This can be done with a torque wrench, a hand spanner or even by a

hammer and flogging spanner. This is because it doesn't matterwhat

resistance is encountered when trying to turn the bolt/nut: the sensor

only changes colour once the appropriate bolt load has been achieved

.

As noted in a previous post, one may have the "proper torque" yet thebolt may still be loose. Actually, if less friction is encountered, a

"properly torqued" bolt can even be too tight. Load verification such

as elongation measurement or by visual inspection utilizing this

technology eliminates these insipient risks.

__________________


HookerGuru



Thanks for the clarification. I certainly understand the risks.

I really like the load verification by elongation, and will certainly keep

these in mind for future design tasks. There's always some worrisome

place where we can't use normal retention practices (safety wire,

loc-t ite, etc)

Hooker

AviatorCommentator

Join Date: May 2008Posts: 86Good Answers: 2


Actually, there are two additionnal concerns that may be particular to the

aviation field :

1) Showing a MINIMUM of 1.5 threads with nylon insert locking nuts

insures that any shear force on the pieces assembled with the bolt is

effectively applied against the shank of the bolt (unthreaded part).

2) Showing a MAXIMUM of 3 threads with nylon insert locking nuts insures

that the thread of the nut have NOT started to make their way into the


18/26

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#42In reply to #41

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In reply to #42

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untheaded part of the bolt (shank), hereby damaging both nut and bolt.

Interesting discussion !

AnonymousPoster


Are you aware that there are special structural bolts available that are

torqued to a point where the threads deform, creating a permanent lock.

These bolts cannot be reused if undone and must be replaced with newbolts/nuts. They are used in bridge construction and in buildings steel

joints where they are hidden from sight and must be relied upon to not

loosen.

nick nameGuru



Indicate the source, manufacturer, address, catalogue, .... Thanks Nick

Name

bwireGuru



Are you aware that your description apply to all properly tensioned bolt

joints?

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redfred Re: Bolt Length01/07/2010 2:43 PM

bwireRe: Bolt Length01/07/2010 2:46 PM

nick nameGuru

Join Date: Mar 2007


No, bolts can be used under conditions several times.

What the guy said (in an improper way which could be considered as

arrogant or at least impolite) is that some bolts when torqued over a

threshold deform the threads so that a mechanical lock appears. I was

informed of such bolts but I was not able to find sources this is the


19/26

#45In reply to #44

#46In reply to #45

Location: City of LightPosts: 2868Good Answers: 107

reason for my question. In fact as far as I know it is the nut which is

deformed so that a zone is plasticized and generates in the thread a

friction torque INDEPENDENT of the preload. This is a guaranty for a

reduced risk to have the bolt/nut pair going loose. Anyway such

solutions cannot apply for machines and are used in structures where

the loads have not same dynamics as in mechanical systems.

BoltIntegrity

Power-User


Re: Bolt Length

01/07/2010 6:01 PM

I've encountered "torque-to-yield" in automotive applications but not

in civil. Perhaps the writer refers to the colloquially-termed "twist-off"

bolts in which a necked portion of the bolt's shank breaks loose upon

reaching a certain torque. The nominal threaded portion remains and is

locked by the nut. Notwithstanding the need for specialized assembly

tools, the obvious problem with these is that the nebulous

torque/tension relationship still applies. As such, actual bolt load when

the spline breaks off is still an unknown value

__________________


nick nameGuru

Join Date: Mar 2007Location: City of Light

Posts: 2868Good Answers: 107


The component is called "TC Bolt" from tension controlled and is

intensively used in structures for civil engineering for many reasons

related to cost and quality. Here are a few infos about component

and applications:

The right part is

used as reaction for the torque and will shear at the torque limit

given by the grove at right end of thread.

The shaft is ONLY under tension the torque loop closes at the right

side between thread nut and right end.


20/26

The tool has a

special design with a holder inthe middle for closing the torque loop.

An example of civil

connection between big profiles.

Use in railway

connections.


21/26

#47In reply to #46

A tpical assembly for TC

bolt: a bridge structure.

An other one in London

near to Big Ben

Other structure same

fastener.

The grove is such that the torque at shear is near to the one

needed to stress the bolt in the right strain range.

The only problem with those bolts is that in most cases they are

short and thus cannot be used where transverse loads have a high

frequency. It is but possible to use them in calibrated holes and then

the side movement which is the most dangerous for loosening is

maintained at a very low level.




22/26

#48In reply to #47

#49In reply to #48


The biggest problem is:

" ... the nebulous torque/tension relationship still applies. As such,

actual bolt load when the spline breaks off is still an unknown

value..."

Granted, there is much meat left in the safety factor of civil bolting

applications. Thus, there may not be as much of an issue here as

there is in critical industrial bolting applications. However, it's

misleading when the description suggests "... used... for...reasons

related to...quality".

Quality is knowing what you've got. This is still, unfortunately,

"guessing".

__________________


redfredGuru



Point well made BoltIntegrity. These bolts show what torque hadbeen applied which need not be the actual bolt load. I would

expect that the bolt load will change on these bolts as normal

load conditions change on these civil engineering projects.

But I wish to compliment you, Nickname, TVP45, Trevor Walden,

and Daedalus for such an informative discussion. This type of

engineering insight is precisely why I linger on this blog.

__________________

There are 10 types of people. People who understand binary and

those who don't.

FJDominguesCommentator

Join Date: Dec 2009Location: HoustonPosts: 61

Good Answers: 4


Ok. All this is good discussion, but does not answer the original

answer.

The reason for the extra thread (exposed past the outer face of

the nut) is to prevent yielding of the threads under the nut at

the end of the bolt. The normal standard is to assure that 3

threads are exposed. With fewer threads exposed, there could

be a risk of the bolt threads yielding in shear under the nut.

Exposing any more threads is not necessary and could bewastful. Note here that the bolt yields before the nut (in

correctly specified connections).

Also note that, for many applications, this characteristic would

preclude reusing the same bolt for the same application.

However, since yielding usually does not occur, this normally is

not a problem for applications for which this limitation is not

specified.

Some comments on bolt tension: See my next post, which I

consider to be off topic somewhat.


23/26

#50In reply to #49

#53In reply to #49

#52In reply to #47

__________________

Little about much, much about little

FJDomingues Re: Bolt Length01/08/2010 7:20 PM

Anthony@ALNOCommentator

Join Date: May 2009Location: Gosford,Sydney, AustraliaPosts: 58


Where can i get a copy of the normal standard?

Anthony@ALNO

www.alnoproductservices.com.au

nick nameGuru



You are right but in this particular case the dispersion is a lot less

important than in other cases for following reasons:

Geometry: the grove is manufactured with a tolerance of about

0.1mm which represents 1% of the diameter even for the smallest

type. surface. So that the torsional modulus will have about 3%

dispersion.

Material properties: elastic limit has a dispersion of about 4%

since the bolt are made from a high quality steel and heat

treated.

Friction: nut and washer come from same supplier and have samesurface conditions, in general the washer is large and thick (to

assure a quasi plane contact since the structural steel is weaker

than the bolt or nut). This guaranties a narrower dispersion of

friction coefficients and contact conditions between nut and

sliding surface (washer only!). Same conditions for the friction

between threads. U estimate the dispersion at about 4..6% based

on measurements.

All together the dispersion of the applied tension will be

(3^2+4^2+6^2)^0.5=7.8%.

Due to the very very high redundancy of structural joints (yousaw the number of bolts in one example) the result will be very

near to the average so that it is not so bad.

Of course this fastener is not of use for applications with only a

few bolts as in automotive, but could be of interest in airborne

assemblies where the redundancy is also high imposed by the thin

walls with limited local carnying capacity. To make a comparison,

for a car in general an assembly consists of about 3 to 4 bolts

working together (one side of suspension), for a small plane one

wing is fastened with over 150 bolts to the main body and for

A380 there are 2500 bolts on one wing side.


24/26

#51In reply to #44

#56

#70

#71In reply to #70

bwireGuru

Join Date: Dec 2007

Location: Upper Mid-westUSAPosts: 7506Good Answers: 96


Lug nuts etc. are torqued and re-torqued many times but many

applications require replacement of the fasteners each time.

__________________


nilayveeraActive C ontributor

Join Date: Jan 2010Posts: 16


Hi There

There is indeed need for that extra threaded length, because there could

be vibrations in the assembly, Vibrations can b caused due to thermal

contactions and expansions due to c limatic changes. That extra lengthcan prvent the nut from falling off and thus save your assembly from the

failure.

drbobwooleryCommentator

Join Date: Feb 2010Location: Vallejo, CAPosts: 90

Good Answers: 6


From a retired Union Steamfitter's perspective, you guys are straining at

gnats. This applies to the 1/2 to 1 inch or so B7 studs and Heavy hex nuts

that hold together most of the flanges in US refineries. Only at nuclear

sites have I seen torque wrenches used for nuts smaller than about 3

inches. Elongation measurement is obviously best. One obvious reason to

leave extra length is to allow for a slip blind and its extra gasket whenisolating parts of systems. On 150# to 600 # series flanges, the flange

nuts get pulled up in stages until final tightening with two combination

wrenches linked together for leverage. If it leaks on hydrotest, go round

and round with a knocker wrench (what one poster called a thrashing

spanner) until it tightens up. Most of the time this extends to the largest

pipe sizes. Make the contractor see that the studs are buttered with

appropriate compound, Coppr cote, Ni antisieze or whatever from one end

to the other. Demolition of old worn out units often reveals studs with

intact threads near the nuts, and rotted away in the area that didn't get

any bolt dope.

JohnDGGuru

Join Date: May 2006


"you guys are straining at gnats ..."- that's as maybe, but it doesn't

wash with a customer's inspector when you're trying to get a new piece

of gear passed for payment.

__________________

There is nothing new under the sun but there are lots of old things we

don't know. Author unknown.


25/26

#72In reply to #71

Reply to Forum Thread

Copy to Clipboard

Location: Reading,Berkshire, UK. Goingunder cover.Posts: 8914Good Answers: 257

drbobwoolery Re: Bolt Length04/18/2010 10:14 AM

72 comments

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Comments rated to be Good Answers:

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#4 "Re: Bolt Length" by TVP45 on 01/05/2010 10:35 AM (score 2)



Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agreewith them, rate them!

#13 "Re: Bolt Length" by Trevor Walden on 01/06/2010 4:47 AM (score 1)

#14 "Re: Bolt Length" by Randall on 01/06/2010 5:55 AM (score 1)

#19 "Re: Bolt Length" by Hooker on 01/06/2010 9:21 AM (score 1)

#26 "Re: Bolt Length" by redfred on 01/06/2010 11:23 AM (score 1)




Users who posted comments:

Anonymous Poster (6); Anthony@ALNO (3); Aviator (1); BoltIntegrity (8); bwire (9);

CaptMoosie (1); crimich13 (3); Dedalus (3); drbobwoolery (2); FJDomingues (2); Hooker (4);

JohnDG (2); nick name (11); nilayveera (1); omw7 (3); ozzb (1); Randall (6); redfred (4);

Trevor Walden (1); TVP45 (1)

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