Bearing Strength of Bolt CISC 1

[Veer007]

Hey Guys,

This is a table 3-6 from CISC, shown bearing strength of bolt depends on the thickness of material which has grade 300W.

For shear/moment connection, I have a web thick of w-beam is 16mm and 10mm thick shear plate.

and 4 no. of 19mmØ A325N bolts satisfy the applied force, But what was my concern is

Don't I use this dia of bolt right? as the value is shown max. up to 14mm thickness, the bearing strength of 19mm or 3/4" bolt is 288kN.

Anyone please assist me?

This only for bearing type connection, right? we don't need to consider this for slip critical?

Thanks in advance!!

 

[r13]

The bearing resistance is governed by the thinner part jointed, in this case, the 10mm shear plate.

This only for bearing type connection, right? we don't need to consider this for slip critical?

When overload, the bolt will ultimately be forced into bearing type connection, so you shall consider it.

 

[Veer007]

This is what I asked earlier when overloading, a slip critical connection will be changed as bearing type, but most of them refused it.

Thanks in advance!!

 

[r13]

If slip-critical connections fail (by slipping), they revert to bearing-type connections, with structural forces now transferred through bolt shear and connection plate bearing. Thus a slippage failure of a slip-critical connection is not necessarily a catastrophic failure.

Slip critical connection usually services a purpose, or special function, that slippage is a way/desirable feature to prevent catastrophe due to un-controllable event, such as the sudden shutdown of a piping system. It is, therefore, a fuse designed to safe guard the connection from failure.

Note that, depends on the hole size and intensity of the overload, the bolt might not get into bearing immediately after slippage, as the energy is dissipate during motion, even a short distance.

 

[Veer007]

Yeah, in CISC, if the connection to be designed as slip critical, we have to check this with bearing type at ultimate loading.

So if we have to design a connection as slip critical, we can use unfactored or service load, right?

Thanks in advance!!

 

[r13]

Yes. If the design was done by ASD.

 

[jayrod12]

WE don't have ASD up here anymore.

An excerpt from the steel design manual on slip-critical, emphasis added by me

"....slip-critical shear joints transfer the specified loads by the slip resistance (friction) of the clamped faying surfaces...., In addition to the slip resistance of the joints, their factored shear resistance as bearing-type joints under factored loads for all applicable ultimate limits states must also be checked."

So the word specified in the first bit to me means your unfactored SLS loads. You still need to check the connection for the factored loads in all other failure modes.

 

[Veer007]

Perhaps, design was done by LRFD, do we need to use ultimate loads for slip critical? Then it will end up with lot of bolts.

As slip resistance of bolts are very lesser than shear resistance/bearing resistance of bolts.

Am I right?

Thanks in advance!!

 

[r13]

Any reason for providing SC connection?

 

[Veer007]

Not sure, there is a note from contract drawings, which shows all moment connections are slip critical.

Thanks in advance!!

 

[dik]

I've been an engineer for over 50 years and have never used ASD, except for checking other ASD.

Dik

 

[Veer007]

.

Thanks in advance!!

 

[jayrod12]

As I indicated, slip critical checks are against the service level loads, you still need to perform the other type of connection checks at factored loads.

If you weren't provided the service and factored loads, ask the EOR.

 

[Veer007]

This makes sense.

Thanks in advance!!

 

[jayrod12]

I'm not sure what else you are looking for?