Lag Shield Anchors in common red brick 2

[smb4050]

Does anyone have or know where I can find design values or test results for lag shield anchors in brick masonry? The situation is I need to bolt a wood ledger plate to an existing red brick masonry wall to fasten the wood roof deck to. Purpose is to transfer lateral loads into the masonry, with a smaller vertical force also. Thanks,

 

[youngstructural]

This will be the second time I plug Hilti today, but I have to say that I always use their HIT-HY 50 with AN anchors in these situations. I have found them to be well thought out, and Hilti has great support.

Can't help you with the product you mention. Hopefully someone else can.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[concretemasonry]

A couple of complicating comments.

Is the "red brick" wal just a veneer or is it some sort of real bonded masonry wall. Wall ties attaching brick veneer are not at all reliable since they are not structural connections.

"Red brick" is a only visually descriptive term. Red colored brick can have widely varying properties (2x to 4x) depending on the manufacturing process (pressed, extruded) and the method/amount of firing. Some of the old red brick is very soft and weak, while other red brick is among the hardest and highest strength.

Dick

 

[smb4050]

In an effort to be brief I neglected to provide all pertinent information. The application is for an 103 year old 6 story warehouse building, 17" (3 wythe) thick wall that is being restored for use as condo/office building.
Youngstructural, I don't know about HY 50, but did you mean HY 20 with a HIT A threaded rod? I've looked at it and felt it doesn't accurately apply to this application, and when I contacted Hilti, they suggested HY 150 system and do load tests which I plan to do. But I am looking for a rational basis to begin with. In the deep recesses of my mind, I recall seeing something for lag shields but I can't find it or recall where I saw it. Thanks for the replies!

 

[gwynn]

I don't have my Hilti book in front of me, but the other option with them is to use thier HLC sleeve anchors. These have been tested for use in red brick and the standard Hilti book gives recomendations for using them.

For reference, the HLC anchors give lower allowable loads than thier chemical systems. As far as I know Hilti has not done tests on HY-150 with red brick, nor with the new HY-150 max, though they have with other chemical systems. Given that, I'm not sure why they would recommend HY-150.

 

[PackerFan]

I may work for a company that starts with "H" ends with "I" and has "ilt" in the middle, so for everyones info HY-50 is a product only sold overseas specifically designed for solid masonry, something we don't have as much in the US. HY 150/MAX/20 are very chemically similar. As long as a field test is done any would be a posibility. If you have any reason to believe any voids exist, you must use a screen tube, otherwise the goo will dump out into the void and none of them will work well.

 

[youngstructural]

Hey Packerfan; Thanks for the back-up, HY-50 really is the right product for this application, too bad it's not available.

Since you are dealing with Historic Brick (which I had assumed, although Dick was quite right to call foul on too little info to be giving advice!) you need to be aware of a variety of other issues also. There is a great, very recent, thread called "1900s Masonry" I suggest you read it as well.

As for what to do with your problem, no matter which way you go, I strongly suggest using a steel rotation strip. This is basically a continuous strip washer that prevents any pull out forces from being applied to the anchors due to vertical loading. Through bolting every so often wouldn't be a bad idea either to deal with the inevitable (in reality) seismic loads in the tension/compression load direction of your selected anchoring.

If you do pursue Hilti's recommendation of HY-150/MAX/20, make sure you have them provide a recommended design procedure. Even if they are chemically similar (as above) to HY-50, the design procedure is not the same.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[MiketheEngineer]

Try POWERS fasteners (

http://www.powers.com)

- they make some for brick. But as mentioned - the wall itself may be the weakest link and not the brick...

 

[smb4050]

Thanks for the replies.

I visited Powers Fasteners and the 1900s Masonry thread, and both helped.

Youngstructural, would you mind explaining more on what a steel rotation strip is? From you reply I envision an angle or small channel being installed over the wood ledger beam to prevent rotation. Correct?

Thanks again,

smb4050

 

[youngstructural]

Close, but a small angle will in and of itself have some rotation... It's more like just the vertical leg of the angle, cut slightly short, so that you have a continuous "washer".

Picture a 50mm (2") flat bar, say 5mm (~3/16") thick with holes centrally for your anchors to pass through. When your ledger gets loaded vertically, there is almost no rotational stiffness at the support. Exactly what you want, since this prevents tension forces on the anchor.

If it's still not clear I'll upload a sketch. I know I tend to be a bit too wordy... I guess it's a weakness of my Eng-tipping help.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[concretemasonry]

All of the theoretical concerns will not do anything without knowing the ability to attach the ledger to the existing wall. The wall is there and the attachment materials or methods could change.

The wall is there and has whatever properties it has. Current fasteners are proven to have consistant physical properties - if the can be developed by the material they are attached to. All the test reports and documentation are of little value if there is not enough information available to make an engineering decision regarding a proposed detail.

It is insane to go through all of the theatrics, distortion analysis and capcities of the fastener (which are probably very accurate to within 5%) when you have no idea of the properties of the material is is attached to other than knowing it is shaped like a brick and is colored "red" (which may get you into a + or - range of 50-75%).

If it is important from a cost/life-safety standpoint, run some tests, otherwise, use the tried and true engineering philosophy of "belt and suspenders".

 

[youngstructural]

Concretemasonry:

Of course "we" need to know the material capacity, but you can take conservative assumptions given the age and condition of the wall. That done, all the rest of these concerns become important. If your numbers don't come out based on the lowest reasonably assumed material strenght don't work out for a reasonable solution, then we might consider moving to testing, as you recommend. Testing is expensive, and most of the time not necessary. Just because materials are old does not automatically mean they cannot be subject to modern engineering techniques.

Using the right epoxy is not theatrics; It's a necessity to give the wall and new attachments a long life.

Using a rotation strip isn't theatrics; It's good detailing.

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[concretemasonry]

youngstructural -You are completely correct about the general problem.

Unfortunately, there is a wide range of properties for "red" brick. They vary by factors of 5 to 10 when it comes to shear, ability to bond to adhesives and compressive strength(which is really not important because of the testing procedure). A "red" brick in some areas is a hand pressed unit that is marginally fired, while in other areas it is an extruded, dense, very stable and strong material with completely different properties. A prudent engineer would look at the attachment system manufacturer's submittals and decide if the brick is what is in the subject wall. If not applicable, the only logical arroach is to be conservative instead of requiring a costly individual testing program.

If there is not sufficient documentation, the engineer should insure that the attachment will withstand the loads imposed. In this situation, the loads are probably not great enough to challenge the 17" wall strength, but the connection is the critical point. If it was a Boral brick wall in an identified location (U.S., Poland, Austria, Australia), it would be much easier to comment on the wall material properties. Eastern U.S. "red brick" walls are often composed of very soft brick that have low strengths, while 200 miles away, the properties are totally different. The fact the wall is a 3 wythe bonded brick wall(17" thick) indicates it may be typical of the some of the areas where the "soft" red brick were used in older structures.

Often, manufaturers select the ideal materials to use in product accepance tests rather than the more costly common range of materials the product is attached to.

Dick

 

[youngstructural]

Dick: A star for your post. If a reader didn't know the issues behind the selection of a conservative, low-end material strength for red brick, your post would certainly make them aware of the sensitivities involved.

And you're absolutely right about most fasteners; That's whey I have been so insistent upon HY-50; Hilti has published information in their International manual on lime-sand-clay low strength brick. It's a great anchor for restoration engineer's tool box.

Hopefully we'll get an update from smb4050 to hear how the project is getting along...

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[KCRatnayake]

As I can recall, Hilti has developed HY 50 system due to following reasons and may be more.
1. Chemistry - They had found that HY 150 has some probems when they are in (red) bricks
2. You don't need a very high strength material as most of clay bricks have strengths lesser than that of concrete (i.e. base material strength)

As YS stated, HY 50 is a great system; very helpful in restoration works.

Clefcon