Single plate moment connection
Single plate moment connection
(OP)
I am reviewing some moment connections that were submitted to me and there is an unusual moment connection that I have essentially rejected, but wanted to get the opinion of you guys on.
The connection is a WF beam to an HSS column, and the designers used what is essentially a large shear plate with no flange plates at all. The large shear plate is slotted through the HSS and bolted with two vertical rows of bolts to the beam web. The bolt rows are spaced up to 9" apart.
My biggest issue is the transfer of the bending stress in the flanges into the web.
I've never seen such a connection before, and could find no reference to one anywhere.
What do you guys think?
Thanks,
Patrick
The connection is a WF beam to an HSS column, and the designers used what is essentially a large shear plate with no flange plates at all. The large shear plate is slotted through the HSS and bolted with two vertical rows of bolts to the beam web. The bolt rows are spaced up to 9" apart.
My biggest issue is the transfer of the bending stress in the flanges into the web.
I've never seen such a connection before, and could find no reference to one anywhere.
What do you guys think?
Thanks,
Patrick






RE: Single plate moment connection
RE: Single plate moment connection
RE: Single plate moment connection
I can see where they are trying to develop some moment capacity by spreading the bolts out, but I still think the moment transferring mechanism is not there.
RE: Single plate moment connection
RE: Single plate moment connection
Thanks for your input. I'm not even sure how one would go about verifying the stress transfer from the flanges to this plate short of a solid model.
RE: Single plate moment connection
You can direct him to the AISC Manual 13th Ed, which has several examples of how to detail proper moment connections to HSS members.
RE: Single plate moment connection
RE: Single plate moment connection
I am assuming that the connection is part of a moment frame.
RE: Single plate moment connection
The bolts should be friction grip.
RE: Single plate moment connection
RE: Single plate moment connection
RE: Single plate moment connection
It is misguided, poor detailing. It ignores the most basic concepts central to a moment connection.
RE: Single plate moment connection
RE: Single plate moment connection
Then, having transfered the moment into the plate, the next step is to check the plate stress. If the plate is "t" thick and "h" tall, I = th3/12, and stress = Mc/I = Mh/2I.
Obviously, it can work, and should work well, especially if the moments are low and the arm is wide.
Calculating rotation is more complicated. First, the shear diagram between the bolts (say "s" apart) is a horizontal line, then zeros between the column and the vertical line of bolts closest to the column (say "s0" apart). Then, the moment diagram starts 0 on the outer bolt line, tapers diagonally up to M at the inner bolt line, then is contant to the face of column. Since the rotation is the area under the moment diagram divided by EI, we have theta = M(s0 + 0.5s)/EI.
See page 12-2 of AISC #13 Code, which shows a graph of rotations. This single-plate moment connection is not "simple" nor is it "fixed", but is closer to fixed than simple. Generally, it rotates more than the end-plate connection resisting the similar moment.
We can evaluate how stiff it is as follows. Here the stiffness K = M/rotation. By AISC #13, "stiff" is K = 20EI/L, while "not-so-stiff" is 2EI/L. The stiffness of the connection can be assessed by seeing where the it falls between these two extremes.
In fact, torsional bolt groups are often used to make moment-resisting beam splices. One slaps on a channel each side of beam webs, extending equally onto each beams, then configures a group of bolts to resist the splice moment. I know of several engineering firms who use this detail.
RE: Single plate moment connection
- It requires a very significant connection stiffness reduction to get a significant reduction in the attracted moment.
- Any connection moment due to lateral loading will never be significantly reduced.
- It's a non-issue if the connection stiffness is matched to the column stiffness.