TORQUED? anchor bolts

[penpe]

Per ACI D.8.2 for cast-in anchors that will be torqued, minimum edge distance is 6 x bolt diameter. Not torqued min is same as cover requirements of re-bar. Other requirement for side face blowout and concrete breakout strength must be met, which will drive edge distance. Having met the requirements for concrete blowout and breakout is edge distance less than 6 x bolt diameter okay?

The big question is: when is an anchor bolt considered to be "not torqued"? It seems that any time you tighten a nut onto a threaded rod torque is applied, right? Or is it only considered "torqued" if a numerical value is stipulated; i.e. lb-ft of torque required?

 

[RPMG]

Anchors should be assumed torqued by default, if no other information is specified, because the contractor may torque the anchor when fastening the fixture. If it is specified that the anchor may not be torqued, such as by clamping down a plate with the leveling nut, then the torque is not felt by the concrete.

 

[BAretired]

I would say that a bolt is considered torqued when the turn-of-nut method is used and inspected.

BA

 

[RPMG]

Also, torqued refers to a past condition. If the nut is tightened, torqueing the anchor, and then loosened, then the final status is torqued because the anchor has been torqued.

 

[dik]

turn of nut, but not the same as 'Snug Tight'... a little less than that.

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

-Dik

 

[dik]

From Portland Bolt:

"The majority of anchorage applications in buildings do not require special anchor rod nut installation procedures or pretension in the anchor rod. The anchor rod nuts should be “drawn down tight” as columns and bases are erected. This condition can be achieved by following the same practices as recommended for snug-tightened installation in steel-to-steel bolted joints in the RCSC Specification. That is, most anchor rod nuts can be installed using the full effort of an ironworker with an ordinary spud wrench.

When, in the judgment of the owner’s designated representative for design, the performance of the structure will be compromised by excessive elongation of the anchor rods under tensile loads, pretension may be required. Some examples of applications that may require pretension include structures that cantilever from concrete foundations, moment-resisting column bases with significant tensile forces in the anchor rods, or where load reversal might result in the progressive loosening of the nuts on the anchor rods.

When pretensioning of anchor rods is specified, care must be taken in the design of the column base and the embedment of the anchor rod. The shaft of the anchor rod must be free of bond to the encasing concrete so that the rod is free to elongate as it is pretensioned. Also, loss of pretension due to creep in the concrete must be taken into account. Although the design of pretensioned anchorage devices is beyond the scope of this manual, it should be noted that pretension should not be specified for anchorage devices that have not been properly designed and configured to be pretensioned."

and

file:///E:/Downloads/eMail/MnDOT%20Anchor%20Rod%20Tightening%20Handbook-11138998-v1%20(5).PDF

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

-Dik

 

[RPMG]

penpe's asking how to not torque an anchor to place it closer to the concrete edge. The question is about concrete splitting.

 

[penpe]

Thanks for the replies. We use grout under baseplates, so that the base plate can be leveled, (and column made vertical), by adjusting a nut under the base plate. So the nut above the base plate is tightened, compressing the base plate between two nuts. The bolt tension created during that process doesn't reach the concrete, so if I'm understanding this correctly these cast-in anchors would be considered "not torqued", and are not necessarily required to be located 6 x bolt diameter away from edge of concrete.

Further complicating this design is that we typically use Sonotube forms for cylinder-shaped foundations, so it's a challenge to determine Ca,max, Ca1, Ca2, Cac; for determining the projected concrete failure area - which eventually leads to determining what is adequate edge distance, partly depending on anchor embedment depth in ACI D.5. It's all set up for a foundation with a square or rectangular surface, which doesn't easily translate to a round surface!

 

[le99]

IMO, I consider a bolt is "torqued" when the tightening introduces a calculated "pre-tension" into the bolt, which consequently develops shear friction around the bolt and pull-out cone on the surrounding concrete. The minimum edge distance is meant to safeguard the hidden/unforeseen defects.

 

[jayrod12]

I thought, and maybe I'm mis-remembering, that using levelling nuts the way the OP described, i.e. nuts on each side of the baseplate, caused all of the vertical load to be transferred through the anchor bolts since they're generally the stiffer load path then the grout. Does anyone else remember hearing that levelling nuts weren't recommended but rather shims should be used?

 

[dik]

jay... that's my understanding, too.

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

-Dik

 

[RPMG]

DG 1 recommends, among other options, leveling nuts with non-shrink grout, which is slightly expansive. It's SOP around here. I have seen that discussion on this site before, but I haven't been able to locate any references.

If the anchors are not permitted to be torqued, it must be noted on the drawing. Specifying leveling nuts is a start, but it's not sufficient.

 

[Tmoose]

Sole plates etc for rotating equipment should not use leveling nuts. I believe every pump, fan, etc manufacturer's installation instructions you find will say so.
Maybe some structures' interfaces are less demanding, but I think I've been reading here that column baseplate systems are frequently scrutinized to ensure handling various 3D loading. Good anchor bolt design and practice is 100% part of that.

API RP 686 "Recommended Practice for Machinery Installation and Installation Design" specifically forbids leveling nuts.

3.8.7 Check to ensure that elevation adjustment nuts under the baseplate that will be grouted in and become a
permanent part of the foundation have not been supplied. This allows the baseplate to be supported by the grout, not
by the leveling devices.​

API even ain't keen on wedges/shims to level mounting/base/sole plates under machinery.

2.6 Mounting Plate Design

NOTE The purpose of this section is to provide the foundation designer with mounting plate design criteria necessary for proper
installation.
..........
2.6.2 All soleplate outside corners shall have a minimum 50 mm (2 in.) radius (in the plan view) to prevent cracking
of the foundation grout due to stress concentration at the corners. All baseplates shall have radiused corners
appropriate to the baseplate design.
2.6.3 All mounting plate anchor bolt holes shall have a minimum 3 mm (1/8 in.) diametral clearance with the anchor
bolt to allow for field alignment of mounting plates.
2.6.4 Mounting plate machined surfaces shall extend at least 25 mm (1 in.) beyond the outer three sides of
equipment feet as installed.
NOTE This provides sufficient area for leveling.
2.6.5 Mounting plates shall be provided with vertical leveling screws, as opposed to shims or wedges. Shims and
wedges shall not be used.
NOTE Shims and wedges, if left in place after grouting, may cause “hard” spots that interfere with the grout’s ability to provide
uniform base support. They may also allow moisture penetration and the resultant corrosion and grout spalling.
2.6.6 Elevation adjustment screws are not permitted under the mounting plate that will be grouted in and become a
permanent part of the foundation. This allows the mounting plate to be supported by the grout, not by the leveling
devices.​

.

In addition, API regards anchor bolts as real structural "fasteners."

5.5 Ensure that the anchor bolt stretch length after grouting will provide a minimum of 10 to 15 bolt diameters of
stretch length.
NOTE Adequate pre-stretch length is imperative to ensure that anchor bolts do not relax and fail due to cyclic stress.
​