special base plate with anchorage

[saad73joss]

Hello Evrybody
I attached a picture showing a base plate with anchorage
Anybody can explain me or give me referneces to understand WHY we use such a detail and how we calculate it
I have never found a clear answer
I will really appreciate your help

 

[structSU10]

That looks like a "fixed" base plate detail to me. The stiffener plates are used to rigidize the base plate. See "Design of Welded Structures" by Blodgett, it had good information on stiffened base plate design.

 

[saad73joss]

i have already designed many stiffned base plates but not one with such an anchorage

 

[structSU10]

Also, this set up is used to distribute the load to more of the base plate, basically reducing the cantilever length to reduce its stress. Again, Blodgett is a great reference for this.

 

[dik]

This type of baseplate has a length of bolt to help develop the tension required to preload the baseplate; it makes for a more rigid connection. The lug at the bottom is to transfer significant shear to the foundation (or whatever).

Dik

 

[ToadJones]

very typical fixed base detail in mill building construction.
It also allows you to preset the base plate and often times there is no weld between the column and plate this detail shows.
AS others have mentioned, rather than just bending the cantilever portion of a typical base plate you use the built-up welded stiffeners to resist that bending.

I don't no consider any base "fixed" unless it uses this type (or other similar) of detail. It helps develop the full bending capacity of the column section.

 

[MJB315]

I don't think this detail (as shown) is actually stiffening the base plate, but it allows for the bolts to remain "unbonded" so that they can be pretensioned during installation. That way, the tensile force is there right at the moment when you need it (to resist overturning moments). Otherwise, the bolts would have to elongate themselves in order to build up the tensile force (rotating in the process) and negating the effectiveness of the "rigid" connection.

"We shape our buildings, thereafter they shape us." -WSC

 

[JoshPlumSE]

The length of anchor bolts can be related to ductility requirements as well. With a longer "stretch length" in the bolts you can get a more ductile performance out of the bolts. At least that's what I've heard.... I don't know that I've seen a published code reference for that though.

 

[ToadJones]

I really do think most of the reason for this style of base plate being used back in the day was to develop the moment capacity of the column section as it would take a very thick baseplate to do the conventional way....at least that's what I ave always thought

 

[charliealphabravo]

...and often times there is no weld between the column and plate this detail shows.

Toad,
Are you sure there is a weld between the column and the plate? It looks like the callout is for the shear lug connection to the baseplate on the far side of the piece.
If so, how is the shear then transferred? just friction caused by the preloading?

 

[ToadJones]

In this image the weld appears to be nearside....welding the column to the base plate.

Where shear transfer to the base plate (and then to the shear lug) is required, the column to base plate weld can be a field weld.

Setting the large base plates loose also helps in aligning the columns as over sized holes and large heavy plate washers can be used for the anchor rods.
Column alignment in mill buildings can be critical for crane runway alignment.

 

[charliealphabravo]

oops, you are right. symbol below the line is for arrow-side weld.
not very good arrow location tho.

 

[paddingtongreen]

The main thing, for me anyway, is that the plate only sees a downward load, the upward load bypasses the plate. You avoid the problem of prying action too.

Michael.
Timing has a lot to do with the outcome of a rain dance.