Base Plate Design - AISC 1

[Ganesh Persaud]

Hello Everyone,

Firstly, is this correct, when bolt configuration of a base late is inside the flanges of the column, it's considered to be pinned, and if the bolts are placed outside of column flanges, it's considered to be a fixed connection?

Secondly, in general, I noticed that pinned base plates has smaller beam sections rather than a fixed base plate connection. Can someone explain this?

Thirdly, Can someone refer me to aisc calculated example as it pertains to a stiffened base plate design. Is it a case where it is designed like a normal baseplate checking breakout and pullout, etc with additional checks to see if it require stiffener plates.

Thank you

 

[mmarlow]

1) No, this is not true.

2) The thicker base plate is to adress bending of the plate itself as it resists the moment

3) AISC Design Guide 1

-MMARLOW EIT

 

[Agent666]

On 2) There is generally a smaller lever arm as well, resulting in a baseplate having less fixity (if sufficiently thin)

 

[Ganesh Persaud]

Alright thanks

 

[Ron247]

Your first question concerns bolt location relative to flange and web. A true pinned connection is very hard to actually make for the more common column base plate connections. One pair of bolts centered on the web with a thin base plate is generally considered pinned but the thicker you make the plate, the more fixed it becomes. I would probably never get "as fixed" as it could if you directly restrained the flanges. On the other hand, if for some reason my column cross-section would not overstress the concrete in bearing and I could attach anchor bolts directly to each side of my flanges without any baseplate, I could make a fixed connection. Fixity is a matter of preventing rotation. So for your first question, it is true in certain circumstances. I believe it to be much easier to make a fixed connection than a pinned one.

on Question 2, when you say "pinned base plates has smaller beam sections", you mean the column on the base plate is a smaller section on pinned versus fixed, that is because the moment at the base is zero on the pin and possibly maxed on the fixed base. Look at a PEMB frame. The column at the top is 40" deep but the column at the base plate is 12" deep. One is fixed and possibly has the max moment while the other is pinned with no moment.

 

[Ganesh Persaud]

Ron I understand your reply, I’ll also have a look at the PEMB frame. Thank you