Base Plate Stiffners 3

[Arun4567777]

Hi Guys!
I am designing Base Plate as per AISC Design Guide 1 with large moment case.
In Bearing the the cantilever bending distance is m or n .What will be the effect if I use stiffners.
I have using 8 bolts per flange.

 

[dold]

For what it's worth, 2" thick Gr. 50 baseplate is a pretty safe starting point for a lot of braced frames and moment frames that I work on. Even simple gravity columns in 5+ story buildings are knocking on 2". 2x thicker plate will be 5x (or more) less expensive than all the stiffeners. Unless you're sending this baseplate to Mars and weight is the most critical consideration.

 

[CANPRO]

If your base has a large bending moment then the stiffness of the connection is or should be of some concern. The methods recommend and discussed above, to my knowledge, only address the strength of the connection. I agree that a thicker baseplate is more economical than stiffeners, but there should be some consideration for the stiffness of the plate as well.

 

[dik]

I suspect your anchorage and concrete would be the greatest concern...

Dik

 

[phamENG]

I'll buy the idea that crazy stiffeners may be cheaper in this case. OP is practicing in India. There are remote parts of India where getting a 2" plate for fabrication may be cost prohibitive, or even impossible with tools available within a reasonable area. Shipping the parts prefabbed may be too much to justify the thicker plate, too. And labor in those regions probably isn't going to be all that expensive.

I had a professor from Pakistan who would frequently compare design ideologies with his home country and the US, and a lot of the differences hinged on the material to labor cost relationships.

 

[skeletron]

@phamENG: To me the residual stress and warping issue is part-and-parcel with the material-cost-availability issue. If you are going to go thin plate with a bunch of stiffeners, your welding process and QA/QC better be top shape otherwise the plates are going to have issues down the line.

What about using T-shapes instead of stiffener plates? You could essentially build up the flange and (maybe) reduce some of the welding/fit-up issues.

 

[STrctPono]

I have never seen two rows of anchor bolts each side of the column. Even with the stiffeners properly designed, those outside anchor bolts are not going to engage very much... if at all. Run an FEA analysis on this base plate and you will see that it is not going to behave like you think it will.

Furthermore, I agree with everyone else that the use of the stiffener plates as you have shown it is egregious.

 

[dold]

Pretty sure the outside anchors are going to receive more tension. Consider strain compatibility. If you had a super thin baseplate and no stiffeners i can see the anchors inside the flange receiving more tension. Maybe?

 

[Arun4567777]

@All
To all the people who are saying this is not safe.You should read MBMA manuals.They have done extensive research on these connections .You can find the papers online. Well yes some of you guys pointed it right ,labor in India is cheap so I will make a considerable saving if I reduce the thickness of Base Plate. Welding is not an issue at all.We have conpleted so many projects with the same configuration ans till date there were no complaints.
I just wanted to know how can we do it.Lets say for therotical reasons only.

 

[Arun4567777]

@dold can you please elaborate on what is strain compatability?

 

[dold]

I'm on mobile. I haven't read this article but look at figure 1 in this link. A fairly basic example of strain compatibility. Strain compatibility is a pretty fundamental theory in reinforced concrete design. Most RC text books will cover it.

https://www.structuremag.org/?p=15443