Pinned connection at base plate

[ben3929]

My client wants me to use a pinned connection at base of a crane frame. The frame base will be attached to a 6” depth ground slab concrete. The client wants the base connection to carry only axial force no moment. How can I support such connection (pure pinned) at the base using anchor bolts. What is the methodology to make the base to act as pinned connection.

 

[ToadJones]

most columns welded to thin base plates are considered pinned.

If the column is independent of the building columns (only supports crane girders) then you can use two anchor bolts placed "inside" the column footprint for a wide flange shape.

How heavy are you column loads?
You are putting this on a 6" slab?

 

[ToadJones]

if this question is related to your other post about prying action, you might be do some things that are not advisable for crane runways.

 

[SteelPE]

In reference to your pinned connection problem.

You can never truly have a pinned connection at the base. You can also never have a fully fixed connection as well. All connection will develop some fixity. I attended an AISC seminar where they stated that a pinned connection will develop a fixity of 0.4EI/L. This equation was based off some assumption in the AISC for calculating K.

Our standard connection has 4 anchors in a square pattern at a given guage (5"-6"). For this type of connection we assume that the base is pinned. Never have had a problem with the type of structures that we design.

Now, having a crane on a 6" SOG may pose some other problems.

 

[StrPE]

You may want to get AISC's Design Guide #7 for Industrial Buildings.

 

[MiketheEngineer]

If you truly want a pinned connection - you could weld two vertical side plates to the base plate. Install you column. Drill a BIG hole through all three and install a clevis pin.

I wouldn't fabricate in that order - but you get my drift. Of course it is pinned in only one direction!!

 

[dik]

Mike... you should have suggested using a couple of smaller holes and a steel ball... 2 directions <G>. Now, just to tie it together to prevent uplift...

Dik

 

[amec2004]

You can refer to attached PDF file for the typical base plate configuration of 2-Bolt Pin, 4-Bolt Pin and Moment Connection anchor bolt pattern.

You can check

http://www.civilbay.com

for a complete calculation of Pin and Moment Connection type base plate design as per AISC design guide 1, and anchor bolt design as per ACI 318-08 Appendix D

 

[hokie66]

As Mike said, you only get a true pinned connection if there is a PIN. The connections in amec2004's post which are called pinned connections are assumed pinned in design, but still resist some moment.

 

[amec2004]

That's true.

In reality there is no 100% pin, and there is no 100% fix. The actual condition is something in between.

Depends on the bolt pattern you go for, the 2-Bolt Pin and 4-Bolt Pin allows more rotation, say 20~30% fix and 70% pin, while anchor bolt spreading out can restrain more rotation, say 70% fix and 20~30% rotation.

If you want to go for the ideal world, you can apply a rotation spring for that.

In the reality, we just go for above posted anchor bolt pattern and assume its 100% pin or fix in the model.

 

[hokie66]

amec2004,

That works fine for many structures, but in the OP's case, it sounds like he really wants to avoid transmitting any moment. If that is the case, he can design a connection where a pin passes through gusset plates, allowing free movement in one plane. If he had to allow free movement in all planes, he would have to use something like a universal joint, but that condition is almost never encountered in building structures.

 

[amec2004]

Attached picture shows one example of true pin connection.

Just being relax on the 2-Bolt Pin or 4-Bolt Pin base plate actually carry some moment.

Do you think in steel structure the PIN connections (shear tab, clip angle, end plate etc) are really PIN ? They are not ! In STAAD or RISA model we all have member release to release moment restraints at member end but actually those PIN connections carry moment and impose a torsion to the connecting girder ...

 

[chicopee]

mill3929, Am I assuming that you are referring to a tower crane and not a jib?

 

[amec2004]

Most Jib crane is a single column with cantilever beam, the base is fixed ...

 

[hokie66]

amec,
Yes, that Detail 3 is the type connection MiketheEngineer suggested, and it could be used at the base of a crane column. I don't believe anyone said this was a jib crane.