baseplate design for axially loaded column

[senthil83]

we have axially loaded basepalte with a small shear force as per the attached sketch.

i have doubt that, while designing the thickness of the baseplate for the cantilever portion as shown in the sketch
can i consider the anchor bolt as a support in the middle.

as i consider the anchor bolt as support in the middle my baseplate thk is coming lesser.

but in the books i found they are not taking it as support.

please clarify.

 

[racookpe1978]

You need a responsible, independent structural engineer in your group.

Your answers seem to imply "I want to design this connection this way because it suits my intentions and because it is my idea (as a mechanical engineer/designer), and I want you (the structural forum readers here) to back me up and support my conclusion."

Your replies are not accepting the technical structural criticism offered about this specific "work-around" non-standard anchor bolt design, but are arguing against it. Look, anchor bolts hold everything up, tie everything down, and are the ONLY link between your mechanism high above - and all of the forces and impulses and accelerations and jerks being applied up high - and the ultimate "dirt" and rocks underground.

Do you really, really want to "try something new" in that location?

 

[KootK]

If your base plate were very thin -- inappropriately thin -- you would indeed get a tendency for upwards curling at the overhanging edges of the base plate. I've seen this in a pre-engineered metal building with 1/4 inch thick base plates. And such a result would be predicted by structural engineering theory. So, with a very thin base plate, you're right, the bolts would clamp the base plate down to the foundation and provide a "support" of sorts.

All that theoretical fun aside, you should absolutely choose a base plate thickness that is sufficiently thick and stiff that it works without considering any clamping force provided by the anchor bolts. This is especially true if you're new to base plate design. Most structural engineers won't go any thinner than 3/4 inch for a serious base plate. Among other things, there's little savings to be gained by going super thin.

I hope that I've interpreted your question correctly and provided something useful to you in terms of advice. When you're done with this, you should consider reporting back with your solution. We can give it a reality check for you.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

i have doubt that, while designing the thickness of the baseplate for the cantilever portion as shown in the sketch
can i consider the anchor bolt as a support in the middle.

I thought you were asking if the anchor bolt acts in compression, taking part of the load. It can do that if there are leveling nuts under the plate, but you did not show leveling nuts.

Instead, you are asking if the anchor bolts act in tension, preventing the base plate from curling upward. If the anchor bolts are in tension, then the total force between the plate and concrete exceeds 400 kN and is carried by an area less than the full area of the plate. The bearing stress would be extremely variable along the length of plate.

In the usual case, the base plate size is derived by dividing the load by the allowable bearing stress, so the full area of plate is needed to carry the load. To minimize deflection of the plate, the thickness should be not less than 1/5 of the overhang m or n.

The actual bearing stress varies slightly because the plate deflects, but the usual assumption is that the stress is uniform over the entire plate. If the concrete under the base plate is in compression at the location of the anchor bolt, then the bolt cannot be in tension unless it is prestressed.



BA