Anchor To Existing Hollow CMU At Mortar Joints 3

[BSVBD]

The post-installed anchor manufacturers have various notes stating that installation of anchors in (horizontal) mortar joints, (vertical) head joints, flange or web of concrete block is not permitted. I understand their concern.

After field verification, when it appears as though the anchor has to be within extremely close proximity of the joint, how does one avoid a horizontal joint without designing a more costly, one-size-fits-all support bracket with twice the amount of required holes to avoid the joint?

Does anyone consider the opening statement overly-conservative?

Within reason, wouldn't the adhesive provide a measure of integrity to the immediate surrounding area of hollow CMU where the anchor is applied?

What about in grouted CMU? Does anyone have concerns, suggestions or other in either application?

I appreciate your input.

 

[SLTA]

Have you called the manufacturers? They usually have extra data they haven't published.

Please remember: we're not all guys!

 

[Guastavino]

Grouted cmu I don't worry much about the location because the grout bonds well to the cmu in my experience.

Ungrouted CMU I would worry some, but can you spec a field test on the bolts by a testing firm?

Also, could you knock out a face shell above it and grout behind the cells in question?

As for the anchor manuf notes, I suspect they are very CYA. They have to know installers don't necessarily read them. Saying install in the center of the cell protects them because that doesn't work out very well in practice. So, if there is a problem, they have something to fall back on. We do the same things with our notes too sometimes, so I can't fault them.

Lastly, perspective, I went to a 100 year old building this week where a previous contractor took out a colomn because it was in the way, he just took it out and did nothing else. The plaster ceiling was holding up the girder. It would take a PH.D to determine the load path of this building which had been like this for a long time before I told them to fix it. In other words, if you have some redundant load paths, that helps me sleep at night too.

 

[Teguci]

Use a piece of slotted channel (like unistrut). Once you have the strut anchored to the CMU properly, you can make your attachment to anywhere along the slot with lots of adjustment and about 1,500 lbs of allowable shear capacity per 1/2" bolt. Just make sure to run the numbers assuming the installation is in the worst position for loading on the anchors and the strut.

 

[KootK]

Use a piece of slotted channel (like unistrut). Once you have the strut anchored to the CMU properly, you can make your attachment to anywhere along the slot with lots of adjustment and about 1,500 lbs of allowable shear capacity per 1/2" bolt. Just make sure to run the numbers assuming the installation is in the worst position for loading on the anchors and the strut.

Love this. Any chance you can get some rollover capacity out of the unistrut as well for some nominal capacity perpendicular to the struts? I imagine not.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Archie264]

Lastly, perspective, I went to a 100 year old building this week where a previous contractor took out a colomn because it was in the way, he just took it out and did nothing else. The plaster ceiling was holding up the girder. It would take a PH.D to determine the load path of this building which had been like this for a long time before I told them to fix it.

Wow, simply, wow!

The progressive collapse requirements for being able to withstand removal of a column seem to make more sense now. But I thought they were to protect against attacks from the enemy, not know-it-all construction superintendents. Perhaps someone will wryly ask what the difference is but to the person killed there really isn't any, is there?

 

[BSVBD]

SLTA - What extra data might you be referring to?

njlutzwe - For the project that instigated this thread, due to the higher than anticipated PEMB purlin load, i have decided to specify grouting the existing in question. However, it is nice when the load is light enough to use screen tubes and epoxy.

Teguci - I'm not picturing your suggestion. Could you provide a detail? (Is this ethically acceptable for the OP to request a detail?) I've never used unistrut in a significant structual application. Is there common engineering data available? I'd have to see you detail, if your willing! Thank you!

 

[KootK]

Is this a linear application like an edge angle or a concentrated thing like a connection plate at a girder? The answer to that may impact the suitability of Teguci's detail.

Is this ethically acceptable for the OP to request a detail?

You're fine, this happens all the time. The trick is two fold in my opinion;

1) Ask politely enough that you don't sound as though your barking orders at the party supplying the detail. I have had a few threads where OP detail requests started to feel like annoying homework assignments.

2) I'd be hesitant to request a sketch from a responder when you yourself have not yet supplied a sketch to accompany your thread. As the responder, it sucks to invest a bunch of time creating a detail for someone only to find that the situation is entirely different from what you've assumed (because there was no OP sketch).

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

Here's a rough sketch for strut to CMU anchoring (not showing your attachment to the strut which can be anywhere along the slot face)

I've never used unistrut in a significant structual application.

If by significant, you are referring to loads, then I'd suggest heavier loads not be supported on hollow CMU. This is a detail for loads less than 3,000 lbs. Strut design comes under AISI calculations except for the serrated strut nut capacity which is covered by testing and a safety factor of 2.

I've calculated the strut torsional properties for the 1 5/8 x 1 5/8 12 ga channel as Cw = 0.202, J=0.00204 and the shear center as 1.23" away from the bottom face. If you load the slot face laterally, you will be about 3" from the shear center. A better strategy is to provide a connection between the strut and the beam that has partial fixity so you aren't depending on the strut and anchors to prevent rolling. For cantilevered elements, turn the strut perpendicular.

 

[BSVBD]

KootK - I agree. I'd rather not expect someone to take the time when it may not be applicable.

However... Teguci, if you would have time, i would appreciate it as it may be a useful detail either to convert to for the OP application, or for the future. I encounter this situation quite frequently. Thank you!

KootK - it is a concentrated PEMB purlin at 5' oc. In the past, i've specified a continuous angle, but, the general requested individual brackets to require only one erector.

 

[BSVBD]

Teguci - Thank you for your time, effort and explanation! I will consider this!

 

[wannabeSE]

For fully grouted CMU, I don't have problems with anchors in bed joints (horizontal). Evaluation reports for post installed anchors allow this. Anchor near head joints (vertical) present problems. With typical blocks, the depth of mortar may not be reliable at head joints and there is no grout behind the head joint. If I had a case where post-installed anchors were needed in the head joint of double open end block, I would call the anchor manufacture (I don't think it is a problem, but I would make the call to see if I was missing something).

 

[MrHershey]

I want to say I've seen them relax those mortar joint requirements a bit. May be going crazy, but could have sworn you couldn't be in or near mortar joints period, but latest Simpson Titen HD ESR (for example) allows you to go in horizontal mortar joints but not vertical. Hilti HY-70 ESR won't let you go in any mortar joints for CMU still but can go in both vertical and horizontal mortar joints in brick.

So may be something that's going away or getting relaxed?