Plate washers on a baseplate 3

[Samwise Gamgee]

I had a question regarding the installation process for a baseplate that is designed to transfer Shear Loads. From what I understand to engage all anchor bolts to transfer shear at the same time, we use plate washers. Are the plate washers welded on the baseplate first and then the anchor rods which are out of plumb forces through them ? Or do they install the baseplate , force the anchors through the holes and then put plate washers and weld them in place ?

 

[dik]

If the loads are small and can be transferred through the anchor rods... plate washers with holes to match the anchor rod can be used and they are fillet welded to the base plate after installation... else, I use a shear lug.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

In order to mobilize all anchor rods to resist shear another option is, filling the annular space with epoxy mortar to get a neat apparence ..

The following excerpt from Seismic Design of Industrial Facilities Proceedings of the International
Conference on Seismic Design SeDIF-Conference)..

 

[bobbyboucher]

baseplate would likely have oversized holes to allow for tolerance of the bolt placement in the field. then the washers with standard holes would welded to the baseplate so that you engage all the bolts in shear

 

[Kuhladula]

I've also designed base plates with a 50% maximum shear capacity on the anchor bolts, knowing that only 2 out of 4 anchor bolts can effectively engage the base plate when oversized holes are used without a plate washer.

 

[JLNJ]

I have seen that detail to fill the annular space with mortar, but have not seen it often. It seems to me that the stress concentration would have the potential to crush the mortar. That said, it is FAR more economical than field welding washers to the base plate and the rods don't have to cantilever through the base plate thickness. I like it.

One, does AISC address or condone this, and, two, what spec do you use for the mortar? The highest strength epoxy grout you can get your hands on?

 

[blihpandgeorge]

i have found getting any real shear loads through anchor bolts to be pretty hard due to the bending effects on the bolt. Once the thickness of the base plate and grouting pad is accounted for the bending stresses can get up there quickly if the bolts are designed to cantilever up. If cantilevering the location of fixity in the base needs to be accounted for as it is not at the concrete surface but within the concrete.

placing a nut under the plate so the bolt can be analysed as fixed at the baseplate help greatly, but only if there is enough space for the bolt in the grout zone. This also increased the lever arm

as a rule of thumb, whenever the baseplate shear exceeds about 25% of the bolt shear capacity, i find having to use a shear key to be the answer.

 

[HTURKAK]

When the grout is confined ,the compressive str. of the grout increases 5 times and EC allows the use of a factor 3.33 .




- I have no idea for AISC address or condone this but , EC allows and has certificate..
- The proposed mortar has Compressive strength (tcure = 28d) 110 N/mm2 EN ISO 604 / HN569..The leaflet of the proposed adhesive is attached..


The OP did not mention the origin of shear load and size of the anchor rods..
You can imagine that , under shear loading, if the force exceeds the static friction between the concrete and the base plate, the base plate will slip by an amount equal to the annular gap then the forces will be transferred to anchor rods and amplified due to a hammer effect. Filling the annular space will certainly increase the total resistance and improve the anchor rod behavior ( no cantilever effect )..

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IMO, if the shear force for Seismic loading, i would prefer annular gap and not weld the washer or fill the gap to mobilize the shear resistance of all anchors.. But this is my personnel opinion..
I think this subject is worth to dig more and would like to hear the opinions of other engineers having seismic design experience .

 

[HouseBoy]

OK-I have a job where I have a lot of shear on the base plates.
What kind of threshold for AB taking the shear vs shear lugs required would you expect?
I typically deal with single family residential loads and details. This one is on a large steel pedestal (30 feet in the air) so... loading and steel details are a bit outside what I normally deal with. I'd really appreciate any examples someone would be willing to share.
WHAT DOES A SHEAR LUG DETAIL LOOK LIKE AND HOW DO I SPECIFY THE INSTALLATION/PROCEDURE?
Thanks,
Steve

 

[Tomfh]

In order to mobilize all anchor rods to resist shear another option is, filling the annular space with epoxy mortar to get a neat apparence ..

Filling it with hard grout/epoxy seems the right answer.