Double-Bearing in butt joint connections

[imstylen]

For tension members bolted by a butt joint connection, one must take into account the fact that there will be two shear planes on the bolts resulting in double-shear. However, there is no similar consideration while determining bearing strength. If anyone could explain why, or point me in the direction of an explanation, I'd be very grateful.

In the attached picture, please find the connection labeled "double lap" for an example of the connection I described.

My professor refers to this as a butt joint, so I'm not sure what the correct term is.

Thanks in advance,
Michael Steijlen

 

[paddingtongreen]

Shear refers to the bolts, on your example there are two interfaces to fail. Bearing refers to the material that is being bolted, failure of the center or of the two outer plies would be a bearing failure.

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

 

[jrbaus]

If you draw a FBD of a double lap bolted connection similar to that shown in your post, you can calculate the shear force on each plane of the bolt and compare it with the single shear capacity. Since the total shear will be evenly distributed to two planes, using "double shear" capacity is just a convenient way of dealing with the double lap situation for designing your bolts.

Just because there are two outer plies does not necessarily mean they have the same bearing capacity (i.e. plates could be different thickness in some situations). The plies themselves are not really in "double shear" or even "double bearing" if such term exists because each ply has only a single bearing surface transferring shear from the bolt(s).

I understand your question however don't think I have done a very good job explaining it....

 

[BAretired]

I don't agree that the connections shown are butt joint connections except perhaps the last one where the plates actually abut one another. Normally, butt joint connections would apply to compression members, not tension members.

The connection labeled "Double Lap" must satisfy three conditions; bolts must resist a shear of T/2 where T is the total tension carried by the connection; each outer plate must be thick enough to carry T/2 in bolt bearing; the central plate must be thick enough to carry T in bolt bearing. In addition to the above, the plates must be detailed adequately to resist Shear Block Failure.

BA