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sundy (Geotechnical) (OP)
13 Jan 09 10:11
The column base plate grout usually needs to be chamfered 45-degree around the edges.

When does the guy on site do the chamfering? (The forms for the grouting have chamfer strips? or the edges of the grout chamfered after the forms removed?)

What kind of tool does the guy on site use in chamfering?


Thanks.
 
structuresguy (Structural)
13 Jan 09 13:08
They can do chamfered grout if they use chamfer strips in the forms.  However, my experience is you get one of two things:  

1.  The edge of the grout even with the edge of the base plate on 3 sides, as they set their forms tight to 3 sides, then left a small gap on the fourth to pour in the grout.

2.  They form up around the base plate leaving a gap all around at least as wide as the depth of teh grout, then they pour the grout flat over the entire formed area, up to at least the bottom of the base plate.  That way, the chamfer angle is "included" in the grout cross-section.  This is my preferred construction method, except I usually tell them to go at least 1/4" up above the bottom of the plate, just to be sure they have full bearing.

I have very rarely seen actually chamfered grout pads.
civilperson (Structural)
13 Jan 09 13:56
What function does chamfered grout perform?
structuresguy (Structural)
14 Jan 09 8:38
By chamfering the edge, it prevents (or seeks to prevent) spalling of the grout at the edge of the base plate.  If it were not chamfered away from the plate, then the edges of the grout could easily crack due to be unconfined.
sundy (Geotechnical) (OP)
14 Jan 09 8:55
structuresguy,

Thanks for your replies.

As you say,you have very rarely seen actually chamfered grout pads,and you pointed out in the next reply, "If it were not chamfered away from the plate, then the edges of the grout could easily crack due to be unconfined."

The question: Have you seen cracked unchamfered edges of the grout very often since chamfered grout pads rarely seen?

Thanks a again.
structuresguy (Structural)
14 Jan 09 14:25
Well, like I said, I get them to pour the grout pad wider than the base plate by at least the thickness of the pad.  This way, even if the top edge of the grout pad gets chipped off during contruction, there is still a continuous load path to extend down from the edge of the base plate at a 1:1 slope.

When I have seen them pour tight to the edge of the plate, yes I have seen some damaged edges of the grout pad.  So this will lead to partial bearing (albeit almost full bearing) of the base plate.  If the plate has very high overturning moments, this could lead to crushing of the grout at the edge of the plate.  Which would lead to less bearing, which could lead to more crushing, etc....

Some of the problem is mitigated if the base plate and bottom of column is encased in concrete, as this will help fill any voids, and also help confine the grout pad.  But if the column base is exposed, like in pre-engineered metal building, then a problem could occur.  Though, the most times I have seen actually chamfered grout pad is in PEMB.
sundy (Geotechnical) (OP)
14 Jan 09 20:40
When the forms set tight to 3 sides,and a small gap on the fourth to pour in the grout, how to ensure that the air underneath the base plate can effectively get pushed out when grout gets in from the fourth side? I have read some grout installation instructions,which indicates that no air should stay under the base plate.

 
structuresguy (Structural)
15 Jan 09 10:07
That is a good question.  You can only look at the grout after the forms are removed to see if it is tight up under the base plate.  If you have large base plates, say 18"+ then you can add a hole near the center to allow inspection of the grout.  I like to make them pour the grout at least half way up the height of the base plate.  That way, I am more assured that they will have full bearing.
sundy (Geotechnical) (OP)
15 Jan 09 16:34
structuresguy

Please see the attached file.

File's link is: http://files.engineering.com/getfile.aspx?folder=8ad87dfa-f5df-424a-819c-c555345ad514&file=Probleme_1_p.90.pdf

Shoulder edges(as you usually do)would lead to crack.

Please comment on this.
civilperson (Structural)
15 Jan 09 17:57
Resin grouts may be left proud, (vertical edge with NO chamfer).
Stl63 (Structural)
12 Mar 09 11:58
Grout holes should be in larger base plates, my expereince is a base plate over 2'-0 square gets (2)-1" dia. holes near the web of the column.  Assuming your bolts are on the corners of the plate or outside the flanges of the column. This allows for reducing air entrapment, especially if you have shear keys on the base plate.  

"Saving the World One Beam at a Time"

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