Moment Connection 4

[Mbasi]

Hi All,

Is it a common detail for beam to column web moment connection to share bolts. I am concerned that the bolts will have to resists double the tension applied from each beam to column moment connection. In the image attached, the beams go into the web where the endplates share bolts.

 

[human909]

Your bolts won't experience double the tension.

Draw a FBD of a single bolt in both situations.

(I'm answering from my phone so I can't readily elaborate further.)

 

[dik]

The same compression on the end plate moment connection acts on both sides of the connection and produces moment resistance for both sides.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

How is that a moment connection?

 

[human909]

Two thick plates a line of bolts. Theat seems like it would be pretty effective in transferring moment and moderately strong too.

If you want to be pedantic the I would
say that it would be closer to the rigid end of the semi rigid spectrum. The lake of bolts outside the flanges will reduce the rigidity and the capacity of the joint.

Going back to the original question. A easy way to think about the design question is to consider the connection as essentially a beam splice with flush end plates. The main difference is that the column is taking the shear while the beams are sharing most of the moment.

(Of course there is a few assumptions above like assuming the beams are significantly stiffer than the column which really depends on their lengths which we don't know.)

 

[Mbasi]

@lexpatrie how is it not a moment connection. it can withstand upto 60kNm?

 

[human909]

Mbasi. FYI some guidelines don't consider it a moment connection unless you have bolts outside the flanges which significantly increases the stiffness of the connection.

As you are likely aware it is the stiffness of the connection that determines whether it is a "moment connection" not the capacity. Though determining the stiffness isn't a quick and easy task.

 

[Mbasi]

@human909 when considering the beams as a splice, if each beam moment reaction is 75kNm would you design the splice as 150kNm ?

 

[dik]

I didn't know that... there is no engineering reason for it not be be a moment connection.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[human909]

The 75kNm reaction is simply the reaction from the other beam. So summing them would not be appropriate. The connection should be designed for the highest moment not the summation of the moment.


A similar analogy is a simple shear connection that sees 50kN. At the connection there's is 50kN from the beam and 50kN reaction from the supporting member. But we don't add the loads. Newton's third law.

 

[dik]

Nope 75kN-m for each side... Having the bolts outside the flanges, may reduce the stiffness of the connection.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[human909]

I didn't know that... there is no engineering reason for it not be be a moment connection.

Agreed. They are the ASI guides based on the AS4100 steel code.

It more a matter of here "is our recipe for a moment connection" based on the code and real world tests. They don't specifically say that bolts inside the flanges is not a moment connection. It just isn't an within their published design guides.

Eg Their beam to column moment connection design guide requires bolts outside the flanges of the beam. Likewise with several other of their moment connections like baseplates. I think for splices they might have flush designs I'd have to check.

(For ease and confidence in design I do largely follow ASI guides. The fact that they are implemented in software packages makes design work simply.)

 

[Tomfh]

I’ve certainly used connections like this as moment connections when the moment is relatively low.


If there is 75kNm each side you design for 75kNm.

 

[dik]

Properly designed, they can accommodate a substantial moment capacity. No need for them to be small.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

I wasn't aware of that and haven't intenionally done that for over 50 years. As I noted, there is no good reason for that.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mbasi]

Thank you all for your input. The Eurocode allows the bolts to be inside the flanges with the bolts in the upper zone resisting tension. Use of extended plates is also permitted which would locate the bolts above the flange. However, in this project, I am not allowed to project the plate above the level of steel as the column stops at that level.

 

[dik]

I quite often extend the column up a couple of feet above the floor level, depending on the connections/construction.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mbasi]

Yes that would be ideal but unfortunately the designer is very strict with the levels.

 

[dik]

In my case, I'm generally the designer. Once a steel fabricator is on line, I often check with the to see if they have any preferences for connections, etc., and if necessary have the EOR confirm these.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

Mbasi (Structural),

The following clauses copy and paste from EN 1993-1-8;

5.2.2.3 Rigid joints
(1) Joints classified as rigid may be assumed to have sufficient rotational stiffness to justify analysis based
on full continuity.

5.2.2.4 Semi-rigid joints
(1) A joint which does not meet the criteria for a rigid joint or a nominally pinned joint should be
classified as a semi-rigid joint.
NOTE: Semi-rigid joints provide a predictable degree of interaction between members, based on the
design moment-rotation characteristics of the joints.
(2) Semi-rigid joints should be capable of transmitting the internal forces and moments.

Although the subject connection can transmit limited moment , it will not satisfy the rigid conn. criterias . The elastic analysis of this type of conn . with classification Semi-rigid conn.

The following paper is useful to get the concept.



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