Bolt Group Analysis 1

[Aviatorbarath]

Can someone explain Why bolt group analysis cant be used when only 2 fastener forces need to be evaluated?

Thanks
Barath

 

[Screwman1]

Please explain your question better. There are a number of ways to analyze load sharing across multiple bolts, but somehow I don't think that is what you are looking for.

 

[Aviatorbarath]

In 2d Bolt Group Analysis, If you look at any standard tools or excel macros; the input for no of fasteners is limited only to 3 or more than 3 fasteners. So what is the limiting factor when 2 fasteners are used in this analysis...

Thanks
Barath

 

[kingnero]

Because when a moment is being held with only 2 fasteners, is is faster to use common sense and a hand held calculator to get the forces involved, as it is to retrieve and open an excel sheet?

 

[dhengr]

What’s a hand held calculator? Can I use my computer game controller to do that? You mean I can’t do this with the $25,000 worth of computers, multiple screens and multiple softwares they put on my desk? I CAD’ed it, I SolidWorked it, I even liquified it, I FEA’ed it to death. What’s the Fy, is that an abbreviation for a dirty phrase? I am obviously not excelling at engineering despite all the Excel macros I have. Isn’t there an app for that? Does app mean aptitude? When do they learn us ‘common sense’ at the uni? Is that a post graduate course, maybe Ph.D. level course, or is even this level of education just more, piled higher and deeper. You mean I only got $60,000 of student debt to get this smart? I traded my Strength of Materials and Machine Design text books right after I failed the finals, for a couple six packs to celebrate the end of finals week; they must not have been any good anyways, cause they failed me. And, now I are an inginer.

 

[Aviatorbarath]

But my doubt is, when both Fx and Fy loads are acting eccentrically; then there will be four unknown reaction acting at the two fasteners namely Rx1, Rx2, Ry1 and Ry2. With only 3 equilibrium equations available, Summation Fx, FY and Mz = 0. How to calculate the unknown reaction forces acting at the fastener location. For clartiy i have added a picture of that. Could any compatibility equation could be used to solve this ??

Regards
Barath

 

[kingnero]

you add both loads, and compare the resultant force to the center of the bolt group (with 2 bolt => in the middle!).
That will introduce a moment, which is composed of 2 forces and a distance.
You have the distance, getting both forces should be easy by now.
remember, they act perpendicular to their distance apart.
When you have both forces and their direction, you could (but I see no reason) project them to the X and Y axes.
et voila, you've got Fx1, Fy1, Fx2 and Fy2...

it takes longer to explain as to write an excel sheet or to take a calculator and get the forces involved...

 

[kingnero]

it takes longer to explain or to write an excel sheet as to take a calculator and get the forces involved...
sorry for the errors, I'm not english!

 

[Aviatorbarath]

I agree what you said is correct..But that is actually BOLT Group Analysis method only right..Bringing it to the C.G of the bolt group then transferring to the fastener location. But doubt is, can it be solved without the Bolt group analysis method..

Thanks
Barath

 

[racookpe1978]

Well, it had BETTER be identical to bolt group analysis: 2 bolts is a simpler subset. Look again at the limits or assumptions behind the more elaborate 3 and 4 group problem.

By the way, the 2 bolt problem (in the real world of heavy-handed pipefitters and millwrights torqueing studs and bolts) is that the shorter bolt of two bolts tightened across a raised face pipe flange will cause the pivot point of the lever formed by the second (longer) bolt to be not at the middle of the pipe centerline, but the opposite (outer) side of the edge of the RF flange.

One assumption of bolt theory is that the flange is bending evenly around the pipe centerline by all 4, 8, or 12 bolts. (There are no 3 or 6 bolt flanges made commercially.) In the real world? Yeah, right, sure, okay. (Another clear case where 4 positives make a negative.)

 

[paddingtongreen]

1. Your diagram does not show the line of force, I suspect that it is equidistant from each bolt, a true centerline but it is not always so.

In a two bolt connection, the plate that is being connected acts as a beam to distribute the load(s) to the two bolts in accordance with the rules of statics. If you cannot take this extremely simple analysis and run with it, you should be looking for a more suitable occupation.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[trainguy]

Give the guy a break :

Looking carefully at the sketch, this is a normal (elastic) bolt group analysis and it doesn't get any easier because there are only 2 bolts. It would only be easier (much easier) if the resultant load were either in line with a line joining the 2 bolts, or perfectly perpendicular to that line.

Aviatorbarath, do you know the procedure for doing an elastic bolt group analysis (with any number of bolts > 1)?

Another comment - try not to confuse loads with reactions. The force vectors on your bolts should be labelled F, not R considering the direction you've drawn them. They should be labelled R only if you drew the actual connecting plate and were showing the reactions on that plate (as applied by the bolts).

Also, racookpe - you're talking about bolts in tension - not at all what I believe is being discussed here.

tg

 

[Aviatorbarath]

Hi Trainguy

You are right about tht reaction arrow is reveresd. i noted it...sorry abt tht..It is supposed to b down and left for the reactions. i jus plotted it to show there are 4 unknowns.

And yea i knw the bolt group method to solve for fasteners>1.. and i have solved for the 2 out of line fasteners which i have shown too..

My actual clarification is; any standard tool if i take to find fastener forces through bolt group method.. it allows me to enter only 3 in the the no of fasteners box.. Does that mean when only 2 fasteners are used with out of line arrangement and eccentric loading,it can be solved witout using bolt group method, or it can be solved with any classical method...

4 unknowns
Only 3 equations are available
Summation of Fx=0
Summation of Fy=0
summation of Mz=0


Can any compatitbility equation or assumptions can be made fr the particular problem to solve this using classical method?


Or it can be solved only using the bolt group analysis method?

I have attached the picture with correct directions of loads and reactions

Thanks

Barath

 

[paddingtongreen]

I don't know what the terms bolt group method and classical method cover, they didn't exist, except in general terms, when I was still working. You gave the impression that you use a computer program as a black box, not knowing what it does so you were lost when you had to find another way. I have attached a generalized diagram of how I would approach this problem. It is easier to see if you resolve the elements of force into one resultant but you could apply them separately and add the results.

Your diagram would show more information if you showed where the load was physically with respect to the group.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[trainguy]

If you're looking for a shortcut around the Bolt Group analysis method, you could resolve the load into 2 vector components that are parallel and perpendicular to the line joining the bolts.

The missing assumption that you're looking for, I believe, is that the component of force that is in line with a line joining the fasteners can be assumed equal at each fastener. This assumption reduces the number of unknowns. But don't forget to include the moment generated by the eccentricity of that and all the other forces.

tg

 

[Aviatorbarath]

HI paddington
The example which u gave is for inline fasteners. But the solution i want is for out of line fasteners. Inline fasteners are simpler to solve like u mentioned in your sample model. But the problem with out of line fastener is; it cant be solved using classical approach unless some compatibility or some assumption are used. I jus wanna make sure; ther is no method to solve this out of line fasteners other than bolt group method
Thanks
Barath

 

[paddingtongreen]

Hi Aviatorbarath, Actually it is easy to resolve. I didn't understand from your first diagram because it had no dimensions.

Resolve the two components of the force into one resultant, it will be 10√2 aimed up and to the right. Extend that line back to the centerline of the bolts. Now resolve into the orthogonal axis system of the bolts, one component will be along the centerline and can be shared by the bolts, and one component perpendicular to the centerline where the results can be obtained as I showed in my first diagram. Then you can re-combine for each bolt.

Come back if you need a better description or diagram.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[Aviatorbarath]

Hi Paddington.

I calculated the reaction forces by taking ur suggestion; it worked. But the reason i got confused is because the applied forces after resolving acts betweent the two fasteners, in my actual problem; it is like overhang beam apporach. The applied load after resolving comes after the 2 fastener location. so ur sample diagram was slightly misintrpreting.

Its My mistake cctually, i didn give proper dimensions, where the loads are from the fasteners; that actually misinterpreted. Anyway Your suggestions are really useful. I checked the results with BOLT Group method, It matches.
I have attached how i approached the results

And Also Thanks Trainguy for you valuable suggestions too. You took the discuccion in the right path

Thanks
Barath