steel column connection 1

[Veer007]

Hey guys, I have thru plate connection for HSS column to w beam. Could i consider this as rigid connction only for checking shear capacity as i have different bolt value while it is flexible or rigid.

Thanks in advance!!

 

[klaus.]

if connection is rigid or not is a matter of the rotation stiffness of the connection
for details see Eurocode

 

[phamENG]

I think there may be some confusion here. The relative flexibility/rigidity of a joint will not change the capacity of a bolt. However, a "pin" (flexible) joint is often designed using snug tight bolts, whereas a fixed (rigid) joint uses slip-critical bolts. The capacities in these two cases are different due to the way in which the bolt is assumed to interact with the plies of the connection. For snug tight, the bolt bears against the inside of the holes in the steel plate and web. In a slip critical joint, the surface is prepared to a certain specification, then the bolt is pretensioned to create a predictable friction force between the plies. The friction is then what resists the loads on the connection.

So it's not about how you model the joint, it's about how you specify the method of tightening the bolts. Hopefully that helps.

 

[Veer007]

hi pham, as per your comment, the rigid connection which connected by slip critical bolts, the bolt value might lesser than flexible joint, But I have rigid one is higher than flexible joint in CISC, any idea?

Thanks in advance!!

 

[Veer007]

Hey, guys above is a reason for my confusing...

Thanks in advance!!

 

[skeletron]

The difference appears to be 20-50 kN. Size it as a flexible support (conservative) and move on.
Use the eccentric bolt tables instead and do an independent check on the beam/plate/support as per the HSS connections guidelines set out in AISC or Packer & Henderson.

Other questions to ask the designer:
What is the relative stiffness of the beam vs. column?
Is there a connection on the back side of the column?
What is the magnitude of the force?

If interest still lies within understanding rigid/flexible supports, search out the literature on connection design. The CISC commentaries, AISC design guides, and Eurocode all point to significant bodies of literature that may be of interest.

 

[Veer007]

ANY BETTER SOLUTION?

Thanks in advance!!

 

[phamENG]

I'm not familiar with the code your using - does it have a commentary section that explains the reasoning behind design tables, equations, rules, etc.? I'd check there. I think klaus had it right from the beginning - those tables appear to consider the stiffness of the joint and therefore limit the resistance of the connection to limit rotation at the joint (just guessing here). The commentary or design table discussion should define flexible and rigid in this context. Compare the definition to the connection you're looking at, and you'll have the answer as to which table you should use.

 

[dauwerda]

Take a read through the following paper, it should answer your questions:

http://digitool.library.mcgill.ca/webclient/StreamGate?folder_id=0&dvs=1576074550581~190

Below is from the paper concerning if a shear tab support condition is rigid or flexible:

I would consider a through plate in an HSS column as rigid as it will develop a couple between the two flanges, but if it were only welded to one face/flange it would be flexible.

 

[Veer007]

Then this is not mean--> when we using shear at the moment connection is rigid one and the normal shear connection is flexible? am I wrong?

Thanks in advance!!

 

[dauwerda]

I believe there has been some confusion over terms as the AISC (US code) does not differentiate the support condition of the shear tab like the CISC does.

The connection that you have presented is a shear tab. When analyzing the structure to determine member forces, connection loads, etc. this type of connection is idealized as a pinned connection (beam end will rotate relative to column).

Once the structure is analyzed and the loads that the connection will see are determined, these loads are used to design the connection. The CISC recognizes that the shear tab is not a true pin connection and also introduces eccentricities, therefore it has tabulated values for two different design conditions - namely Rigid Support and Flexible Support. These design conditions do not describe the idealized connection (fixed vs pinned, this is where there seems to be some confusion), instead they describe the condition of the attachment of the shear tab to the supporting member (this was described in my previous post).

For your condition, you should be determining the required connection loads based on a model that has a pinned connection between the beam and the column. You should then be determining your allowable bolt load based on the Rigid Support condition of the shear tab.

 

[Veer007]

thank you..
Thanks in advance!!