BOLT LOADS CALCULATED BY NACA TECH. NOTE 1051 2

[StressMan2506]

Fellow Stress Engineers:

Is anyone familiar with this document (PRELIMINARY INVESTIGATION OF THE LOADS CARRIED BY INDIVIDUAL BOLTS IN BOLTED JOINTS)? One would expect that the 1st & last fasteners in a row would be equally loaded, the 2nd & penultimate likewise, and so on, but this is not what the method produces. This result is independent of the method used to determine fastener flexibility (denoted 'C' in the document).

NACA Tech. Memo 1135 (THE LOAD DISTRIBUTION IN BOLTED OR RIVETED JOINTS IN LIGHT-ALLOY STRUCTURES) has symmetry built in, but is formulated quite differently. Instead of a single flexibility for each fastener/plate combination, there are separate coefficients for the plate, straps and fasteners.

I am working on a project in which the use of Huth's formulation of fastener flexibility is stipulated. Huth produces values 'C' suitable for use in TN 1051. I am concerned about the inherent asymmetry in this formulation and cannot readily see how Huth can be applied to TM 1135.

Comments/suggestions please.

Thanks in anticipation.

 

[GrandpaDave]

StressMan2506... Looks like this subject has been covered before but it was before I joined this site:

http://www.eng-tips.com/viewthread.cfm?qid=2257

Some of the aircraft guys on here can help you out.
As an old, retired guy I would grab my copies of Bruhn and Peery.
NACA has been around for a long time and it seems to me, but that's
a WAG on my part, all of this should be covered in newer NASA or USAF documents.

 

[rb1957]

i haven't looked explicitly at your TN (but i will today to see how it stacks up against our day-to-day methods).

for fastener loads in a complex joint, i use a compliance model based on Niu's description.

of course, the other way to get fastener forces is to make a simple FEM.

Quando Omni Flunkus Moritati

 

[rb1957]

i'm confused ... it looks to me as though TN1051 develops fastener stiffness values, but you're using Huth for fasterner stiffness (remember the ASTM equation has an error, search for threads regarding "Huth") ...

maybe you mean equation 1 for load distribution ?

Quando Omni Flunkus Moritati

 

[StressMan2506]

Thanks, guys.

GrandpaDave: The thread you provided the link for refers to TN 1458 as a follow-up to TN 1051. Huth quotes 1051 as a reference, but not 1458; I'll check it out.

rb1957: I did mean equation 1 of TN 1051. 'C' therein is bolt flexibility, which may be calculated by the method presented in the TN, or by Huth's formulation, or by any other. Working through equation 1 of TN 1051 yields the asymmetrical distibution. A smaple calc is provided in Appendeix 'B' of the TN.

 

[Nidhi143]

Stressman,

Now i'm also working on this project. I got some doubts regarding to it. In NACA Tech. Memo 1135 (THE LOAD DISTRIBUTION IN BOLTED OR RIVETED JOINTS IN LIGHT-ALLOY STRUCTURES), do you know how to calculate for load distribution with 8 rivets?
Regards,
Nidhish

 

[StressMan2506]

Hi Nidhish:

I've not worked with this stuff since November, so I need to refresh my memory; I'll get back to you...

Louis

 

[rb1957]

ok, now you're starting to get into the material (re your other thread about fastener load distribution) ... could you post a copy of TM 1135 ... i couldn't get it from the NACA site (nor the mirror).

in any case, i presume that it shows you how to calculate the load distribution between a couple rows and you want to extend this.

the way i'd do it is to draw my eight fasteners, draw the lap (skin and dblr), and draw the free body (load in, load out). then there are eight unknowns (the fastener forces), and you can define the load in each fastener pitch (ie P upstream of the first fastener, P-P1 in the skin downstream of the first fastener, P1 in the dblr downstream of the first fastener, ...).

there might be some symmetry that'll reduce the size of the problem.

Quando Omni Flunkus Moritati

 

[rb1957]

ok, i found a fairly legigible copy on archive.org (once on the internet, never off it!) ...

Quando Omni Flunkus Moritati

 

[rb1957]

the key expressions are at the top of pg6, where they're equating deflections along different paths.

Quando Omni Flunkus Moritati