FFR Safety Problem

[CRZN427]

I have been away from my computer for a couple days so I just noticed the unanswered question in this thread, that is "what is single and double shear?".

Single shear connections are made when two pieces are connected with a fastiner (bolt, pin, or rivet) and there is only one plane of resistance to keep the parts fastend.

Take a two pieces of flat bar and make a longer piece out of them by bolting them together. To do this you lap one end of one over one end of the other. There are certain rules as to how much "edge distance" you need to have the maximum strength for the connection. Edge distance is the measurement from the edge of the material to the center of the hole that the fastier goes through. (You wouldn't want to use a 7/8" bolt for a 1" flat bar.)

When this connection is made, whether you have one bolt or more, you have a single shear connection between the two pieces of flat bar.

Now, if you take another piece of flat bar and double up one of the existing pieces so that the odd piece is between the other two (one piece of flat bar going one direction from the joint, and two pieces goint the other way, like a clevis connection) then you will have a double shear connection, again the number of bolts does not affect the description.

When the joint depends on the shear value of the fastiner, rather than the tensil strength of the fastiner, a softer bolt works better because it will deform slightly before fracturing through the shear plane.

If the joint depends on the clamping strength of the fastiner then you want a high tensil strength fastiner to achieve the clamping force necessary to carry the loads imposed on the joint. These kinds of joints are commenly found in structural connections in steel structures, especially where a "moment" is present in the joint. (A moment connection will resist twisting of the joint as well as the shear loads. Not twisting around the axis of the member but twisting in the plane of the joint.)