end plate moment connection

[edwin17th17]

see p4-122 asd for 8 bolt moment connection..

what if i cant put stiffener between end plate and beam flange, is Ma = T * pf (eq 4 p.4-123) still good?

did they consider stifferner plate for point of inflection distance assumption?

 

[Lion06]

Ma=T(pf) is still good. They are saying that this equation is assuming an inflection point at Pf/2 (see step 4 on page 4-123). This moment is simply found assuming the plate is fixed at the beam flange and also at the bolt line. The end moments should then be equal and opposite.

 

[nutte]

I would say "No." The procedure on page 4-122 and 4-123 is for an 8-bolt end plate with a stiffener. If you can't install a stiffener, then you don't have this connection. The connection will behave differently if it has a stiffener or not. AISC Design Guide 4 describes several of these connections (4 bolt unstiffened, 4 bolt stiffened, 8 bolt stiffened), but 8 bolt unstiffened isn't one of them.

 

[edwin17th17]

thx for your responses..

what is the best pf distance assumption for 8 bolt unstiffened if stiffener is not possible...

in case you are wondering i'm designing a piperack and stiffener could cause obstruction for pipes running perpendicular..

 

[nutte]

I would recommend not using an 8 bolt unstiffened connection, unless you can find some literature describing its behavior. I doubt that connection would fully engage the outer row of bolts, resulting in a connection that is not much (if any) stronger than the 4 bolt unstiffened connection.

 

[msquared48]

The main purpose of the stiffener plate above the beam flange is to lower the bending moment the end plate of the beam sees from the bolts, thereby allowing a thinner end plate to be used. The end plate, with the stiffener plate would tend to cantilever more horizontally, whereas without the stiffener, it would cantilever a longer distance vertically, necessitating a thicker end plate.

For the 8 tension bolt scenario, I was surprised to see four bolts up top and only two below since the moment can reverse if this is a lateral force resisting moment frame. Even considering the effect of gravity forces on the connection, I would put tend to four bolts top and bottom unless the connection calcs showed otherwise. Prying action is very perevalent here too in this connection.

Mike McCann
McCann Engineering

 

[msquared48]

As a corollary to my above post, remember too that the tolp and bottom bolts are pulling on the column flange, but, due to the presence of the web of the column, the flange has a stiffener. The flange of the column needs to be checked in bending too.

Mike McCann
McCann Engineering

 

[edwin17th17]

i think i like the idea of structuralEIT better.

 

[nutte]

At the risk of sounding crass, remind me not to stand underneath your pipe rack. You need to pick a solution that solves the problem, not one based solely on how easy the answer is.

 

[edwin17th17]

not really.. not being rude.. i appreciate your response..
but his response was more convincing to me..

 

[UcfSE]

I don't think you should pick what's convenient for you; pick what makes the most engineering sense.

Note 4 on 4-122 suggests stiffener thickness be a finite number, not zero. Not providing a stiffener affects the plate moment by changing the yield lines. Try looking in AISC DG4. You shouldn't assume that something will work when you change the parameters underlying the derivations or the tests. I agree with nutte, and suggest you try a different connection if the stiffener doesn't work for you.

 

[edwin17th17]

as i said.. that is the one makes most sense.. why is
pf distance the same for 4 bolt unstiffened and 8 bolt stiffened??

if what all of you are saying is true then common sense they should differ..

while if i consider the original suggestion.. then it fits both..

 

[nutte]

I think without the stiffener, the plate acts the same as the 4 bolt unstiffened. You might get the same moment in the plate, but you won't get the benefit of 8 bolts (or 6, as the 8 bolt stiffened procedure uses).

It sounds like you don't understand completely how this connection behaves. With that in mind, it is very reckless to assume that the answer that adheres to "common sense" is the correct one.

As noted by me and others, AISC Design Guide 4 is recommended reading. You'll find that the old ASD manual approach has been updated with more precise, albeit more complicated, procedures.

 

[edwin17th17]

i have 3 versions of dg4.. go to page 18 of the older version and you will see "tee-stub analogy" figure..
and you will know what i'm talking about..


i wouldnt be here if i completely understand how it behaves..

 

[apsix]

I don't have access to AISC, but I can reassure the viewers that 6 or 8 bolt connections are routinely designed in other parts of this world without the end-plate stiffener beyond the flanges.
As long as the end-plate is sized appropriately there isn't a problem.

 

[Lion06]

may I also state in my own defense that edwin initially asked if the equation for Ma was still valid, not if the connection would work without a stiffener.
I still think that the equation for Ma is valid. As someone pointed out, you may not be able to take full advantage of all (8) bolts, but that wasn't the question.

 

[JAE]

apsix,

I don't doubt that you can design an 8 bolt unstiffened connection.

The many posters above are questioning whether the DESIGN VALUE CAPACITY determined in the AISC Manual are valid if you leave out the stiffener.

 

[apsix]

JAE
That's a fair comment, but some posters are questioning if there is any advantage in having 4 bolts in tension (compared to 2 bolts) if the end-plate is unstiffened.

From my experience the answer is a definite yes.