Bolted Cover Plates 6

[CDLD]

Hello,

We have an existing galvanized beam we are reinforcing partial length with cover plates and we are connecting it with bolts rather than welds.

AISC states that slip critical bolts are required to develop the force at the theoretical cutoff points but does not explicitly state SC bolts are required for shear flow.

My interpretation is that slip critical bolts are required at the ends of the cover plate but the interior bolts used for shear flow do not need to be slip critical - Agree?

 

[KootK]

Looking forward to KootK's response to Larry's above.

Well, there's not much for me to rail against in Larry's commentary given that he explicitly stated a significant degree of agreement with me.

...I am tending to agree with Kooks arguments.

Per Larry's "any random engineer" approach, the score which was once 5:1 is now 5:2.

Of course, my plus one is Larry -- Steel Jesus -- Muir! That's pretty fun.

 

[BAretired]

Below is a beam which needs cover plates top and bottom in order to satisfy the moment at midspan. It is anchored at each end with slip critical bolts, but no bolts between the ends.

The top plate will need some bolts to prevent it from buckling, so consider the bottom plate which is in tension. If the factored stress at midspan is required to be Fy, the working stress might be in the order of 29ksi. With E = 29,000ksi the unit strain is 1/1000.

If L is short, this may work quite nicely. But if L is very long, the change in length is L/1000, which exceeds the slip of ordinary bolts in slightly oversized holes. For this reason, slip critical bolts are essential throughout the span.

The only reason to use Slip Critical bolts is to prevent slip, but when cover plates are very long, the change in length due to a constant force between anchors may be much worse than bolt slip.

 

[lexpatrie]

As a side note, I actually opened my copy of Design in Structural Steel, Lothers, 1953, and lo and behold a discussion of rivet spacing for cover plates, page 252 - 253.

And then I realized I'd gotten the referenced text wrong on two other threads. AAAAANYWAY..... (I amended those now).