PACKER (OR SHIM) REDUCTION FACTOR, DOUBLE-LAP SHEAR BOLTED JOINT

[StressMan2506]

Fellow Stress Engineers:

I am familiar with a couple of methods for calculating the strength reduction factor arising from packers (shims) in single-lap joints. Presently I am working a concession in which a packer is to be fitted on one side of a double-lap joint. Does anyone know of a method (or adaptation) covering such a case?

Thanks in anticipation.

 

[rb1957]

why not say (for the point of argument) that 1/2 the load goes down one side of the dble shear joint and 1/2 down the other (ie treat as two single shear joints) ?

 

[StressMan2506]

Thanks rb1957, but I feel that a 50:50 split would not be representative in my case; see the attachment. The packer is approx. half the thickness of the central element.

 

[rb1957]

ahhhh ... i hope you we're counting on a dbl shear allowable; reducing the middle layer like that will probably make the joint critical in bearing in the middle layer !

i guess you could either ...

1) look at the overal free body ... if you're going to have simple reactions then that'll dictate the loads, or

2) have the unpacked (stiffer, due to the shorter off-set) side react 2/3rds; but then what'll that do to the overall balance ?

this is i think different from typical packer reapairs, in that the problem with adding packers is that you increase the off-set, increasing bedning in the fasteners.
your repair doesn't look like this, it looks like you've had to repair the middle layer for some reason; you havn't increased the off-sets, but you have reduced the bearing capacity of the middle layer.

 

[StressMan2506]

Thanks again, rb1957.

The subject area is part of a joint made up of 34 fasteners along a curve. Those affected are in the 22nd to 25th positions. I have made the pessimistic assumption that the fasteners in-way-of the packer are ineffective and that their loads are taken by the immediately adjacent bolts, fwd & aft. I have been able to show it good on this basis.