Non-shrink grout at column base

[Darren Emery]

Hello all - its been quite a while since I posted. Been busy with a lot of other non-code related work of late.

I really thought that proper installation of non-shrink grout under a metal column base was a Special Inspection item from chapter 17, but I don't see it in there. Wondering how others handle the inspection of this particular item? For fun, here's a pic of the current condition on site:

 

[ICE]

I have not seen one with a stack of shims or such small diameter anchors. The usual is not standing off that much and it gets grouted without special inspection.

 

[my250r11]

Should be detailed in the structural plans or building supplier plans, with anchor size and strength requirement. They are generally grouted with ??,000 psi non-shrink grout tapered out at least 2". from the pic looks like those are not the approved A??? structural anchors either. If you send pics to the structural Eng. I'm sure he'd freak out.

Never seen shims either, and most of the time the columns need to be grouted before they are loaded with the the floor or roof assembly.

 

[Francis Vineyard]

Would welcome a RDP member add to this but you can search the internet for steel column shims and results such as this from AISC.ORG (ref chapter 16, 17, 22);

Grouting Base Plates

Question:

"We were told by a steel erector that they typically do not remove shims from column base plates after grouting. They also informed us that they do not back off leveling nuts below the base plates during the grouting process. Are these practices acceptable?"

Question sent to AISC's Steel Solutions Center

Answer:

"Yes, shims are left in place underneath the base plates. From a construction standpoint, those shims or leveling nuts hold the load while the grout cures. Their presence after the grout is structural and does not reduce strength. And from an economic standpoint, removal would needlessly increase cost.

Axial compressive forces from the column will be almost evenly distributed as bearing forces on the shims and non-shrink grout. Even if the shims were to take the majority of the load, the assembly will deform in a self-limiting manner through localized yielding or crushing of concrete as the force-distribution model assumed in sizing the base plate is attained."

Bill Liddy
American Institute of Steel Construction

Posted on July 1, 2004

 

[Darren Emery]

If you send pics to the structural Eng. I'm sure he'd freak out. .

I wouldn't say he freaked... but he reacted pretty strongly!

 

[Darren Emery]

Would welcome a RDP member add to this but you can search the internet for steel column shims and results such as this from AISC.ORG (ref chapter 16, 17, 22);

Grouting Base Plates

Question:

"We were told by a steel erector that they typically do not remove shims from column base plates after grouting. They also informed us that they do not back off leveling nuts below the base plates during the grouting process. Are these practices acceptable?"

Question sent to AISC's Steel Solutions Center

Answer:

"Yes, shims are left in place underneath the base plates. From a construction standpoint, those shims or leveling nuts hold the load while the grout cures. Their presence after the grout is structural and does not reduce strength. And from an economic standpoint, removal would needlessly increase cost.

Axial compressive forces from the column will be almost evenly distributed as bearing forces on the shims and non-shrink grout. Even if the shims were to take the majority of the load, the assembly will deform in a self-limiting manner through localized yielding or crushing of concrete as the force-distribution model assumed in sizing the base plate is attained."

Bill Liddy
American Institute of Steel Construction

Posted on July 1, 2004

Thanks for adding this Francis - I had the same concerns!

 

[ICE]

AISC Design Guide No. 3
Serviceability Design Considerations provides the following guidance on this subject: “Until the column bases are grouted, the weight of the framework and any loads upon it must be borne by the anchor rods and leveling nuts or shims. These elements have a finite strength. The timing of grouting of bases
must be coordinated between the erector and the general contractor.” It also states: “Leveling nuts bear the weight of the frame until grouting of the bases.
Because the anchor rod, nut and washers have a finite design strength, grouting must be completed before this design strength would be exceeded by the accumulated weight of the frame. For example, the design strength of the leveling nuts may limit the height of frame to the first tier of framing prior to grouting. Also, it is likely that the column bases would have to be grouted prior to placing concrete on metal floor deck. Properly installed shim stacks can support significant vertical load. There are two types of shims: those placed on (washer) or around (horseshoe) the anchor rods. Shims placed on or around the anchor rods will have a lesser tendency to become dislodged. Independent shims must have a reasonable aspect ratio to prevent instability of the stack. In some instances shim stacks are tack welded to maintain the integrity of the stacks. When shim stacks are used, care must be taken to ensure that the stacks cannot topple, shift or become dislodged until grouting. Shims are sometimes supplemented with wedges along the base plate edges to provide additional support of the base plate.”

AISC Design Guide 1 also provides some guidance.
Section 2.9.1 states: “When designing anchor rods using setting nuts and washers, it is important to remember these rods are also loaded in compression and their strength should be checked for push out at the bottom of the footing. It is recommended that
use of the setting nut and washer method be limited to columns that are relatively lightly loaded during erection.”
Section 2.9.3 states: “Column erection on steel shim stacks is a traditional method for setting base plate elevations that has the advantage that all compression is transferred from the base plate to the foundation without involving anchor rods. Steel shim packs approximately 4 in. wide are set at the
four edges of the base plate. The areas of the shim stacks are typically large enough to carry substantial dead load prior to grouting of the base plate.”


I used to see these often but not now. The stack of shims looks out of place and I can't tell from the picture, but I suspect that there are no jamb nuts. The anchors look small and the washers look smaller yet.
The arrangement in the picture just looks weak. With no leveling nuts it would be difficult to plumb the column.

 

[tim walocha]

I was the owner Rep inspector doing QA/QC on a large project with huge column bases. We had a special inspection agency take cube samples. Breaks came in extremely low. i found out later after the breaks came in that the "skilled tradesman" ( we all the type, the one that tell you immediately, "I have been doing it this way for 20 years!") were using grey water from the elevator pit to mix the grout. They had to hammer and chip away all the grout in about a dozen column pads. JEESH!