Beam Over Column Connection 1

[Veer007]

Hey Guys,

I have the case, where beam bearing on column cap plate which has 360kips as shear and no moment force. Shear force will be satisfied by using direct bearing. Is this necessary to design cap plate thickness and number of bolts still? If yes any way to design? Or just I need to provide cap plate thickness same as beam flange?

below from AISC (Hollow StructuralSection Connections) states cap plate thickness should be min of beam flange.

[highlight #EF2929]"The following is a simplified check provided in Part 9 of the AISC Manual based upon the “no prying action” equation.
Because tmin < tf , there is no prying action in the beam flange."[/highlight]

Beam flange thickness is 2.75"

Thanks in advance!!

 

[Agent666]

R13, let's simply it for you, which way do you see a horizontal force acting and where? Is it laterally, in line with the beam, acting at bottom flange/top flange. Reading back through your posts as instructed people are none the wiser what you are meaning.

And why do you see it being an issue if present, in that it will somehow drive the connection design in your eyes?

Dealing with the lateral orthogonal force to maintain stability has already been discussed right at the beginning of the thread.

 

[BAretired]

You never know when a horizontal force will present itself. I once designed a pipe rack and neglected to brace it out of plane. During a walkthrough, the client grabbed the top of the pipe rack and shook the bejesus out of it back and forth. While he shook it, he asked why there wasn't any bracing, I told him I didn't expect any out of plane horizontal force. He said "that doesn't matter, it's the standard."

I suppose there's a lesson to be learned from that, but I'm not sure what it is.


BA

 

[r13]

Throughout my practicing time, I've not experienced a structural framing system without horizontal load. This is not a homework problem, you simply workout the given conditions; in real word, as an engineer, you have to wonder where is the lateral load from wind, earthquake, and ask why this system seems immune from any of these events. Even without environmental loads, simply supported frames, with variation in spans, will stand without producing any horizontal load. Think again, please.

 

[human909]

My gut tells me that a (4) bolt cap plate where the bolts exist beyond the neutral axis should likely be regarded as a fixed connection. Given a column that's sufficiently stiff, but maybe not so stiff that it would cripple the web of the beam, the force at the end of the cantilevered portion of the beam should cause the beam to pivot about on the edge of the cap plate. That rotation would be resisted by the opposite pair of bolts, thus creating a force couple.

And FEA analysis shows this to be true. Though in this case most alternative connections would introduce an eccentricity that would create almost as much moment. It mostly washes out in the end. Though there would be some edge case.

Another way to think about it is 'pinned' base plate. They really don't behave in a particularly pin like manner they actually quite rigid. And if moment is demanded of them then the connection or the foundation can readily start to fail rather than rotate. There are numerous studies that address this especially with regard to detailing for earthquakes.

But if you really want a real pinned base plate or cap plate that can take an appreciable amount of change of angle at the joint then you need a better solution. than just bringing bolts closer into the center and calling it pinned.
On that note I always think of the columns of the Sidney Myer Music Bowl in Melbourne though there are other examples.

(I've always presumed there was a ball joint at the base, but only from this recent video has this been confirmed to me with actual engineering drawings from the 1950s.)

https://www.youtube.com/watch?v=38KtRNAQCg4

 

[BAretired]

r13,

Of course there will be horizontal loads on the structure, but we have been discussing a particular beam/column joint. The OP is concerned with the connection detail. He is not the EOR and is not responsible for lateral bracing or the design of beams and columns. This has been made abundantly clear earlier in the thread.

You think again!

BA

 

[KootK]

I've always presumed there was a ball joint at the base, but only from this recent video has this been confirmed to me with actual engineering drawings from the 1950s.

As usual, it's maddening how much awesome structure our progenitors were able to crank out with minimalistic drawings. I've done PEMB base plates with three times as much annotation. Metal half ball... graphite lube... Go!

Speaking of interesting science, these red stripes are apparently what happens when I photograph the television with my phone.

 

[human909]

As usual, it's maddening how much awesome structure our progenitors were able to crank out with minimalistic drawings. I've done PEMB base plates with three times as much annotation. Metal half ball... graphite lube... Go!

Lol. Yep, quite impressive of built of such simple drawings. I guess they didn't have the internet to spend waste time arguing over connection details!

I hope you enjoyed the video. It really is an impressive structure both architecturally and structurally. Every part of it is both beautiful and serves and engineering purpose in a relatively simple and efficient way. Though I suspect the average person just sees 'a big tent' and thinks not too much of it. Maybe the guys who design it just really hated moment.

 

[r13]

BA,

I don't see the fruit of arguing back and forth. My standing stands, I encourage the OP to politely ask the EOR to confirm that there is no omission on design load provided, especially horizontal load. As a counter measure, you can dissuade the OP to conduct such inquiry with your justifications.

[28 OCT20 00:06] BA,....the OP's scope is to design the connections, beams and column were designed by others.

[30 OCT20 23:51] It is a question to the EOR, or the designer, as it is inconceivable that a framing system having zero horizontal shear force. As a contract connection designer, I don't have the obligation to, but I would chose to advance my concern to whomever provided the design information.

[30 OCT20 23:35] r13, Instead of coming up with useless comment, explain what horizontal shear you are talking about.

[31OCT2001:23] r13, Of course there will be horizontal loads on the structure, but...

The only reason I talked back is because you named me as the recipient of your comments.

 

[BAretired]

r13,

I have not seen the structural drawings, so I do not know what provision the EOR has made to resist lateral loads. He may have cross bracing or shear walls in another location. Who knows? If he was relying on the members discussed in this thread to act as a rigid frame, I would have expected the columns to be oriented at 90^o to the direction shown.

The OP is free to relay your concern to the EOR; it is not my intention to dissuade him.


BA

 

[r13]

Agree. I would like to hear what is your opinion on the effect of the beam (pink) to the right. Sorry if it has been discussed previously.

 

[BAretired]

The pink beam to the right is a simple span, so far as I know. If it is pin connected, it adds only axial load to the column. If it is rigidly attached, it adds negative moment to the large beam and axial load to the column. Have I missed anything?

BA

 

[r13]

No. You didn't miss anything. It's my overthinking. Thanks.