Clarke Engineering Services, PC
Jobsite Engineering and Consulting
• Just Screw it... (9/08/11)
• Doweling Rebar with Glue? (5/18/11)
• Digging a Little Deeper into Powder Actuated Fasteners (2/20/11)
• Why do Post Installed Anchors Fail? (1/19/11)
• How to select the Right Post Installed Anchor (12/20/10)
• When in Doubt, Test It! (12/17/10)
Just Screw It… While I love these anchors and use them frequently myself, there are some things to watch out for when using them. Here are a few things to keep in mind: So now you have one more PIA to think about during your anchor selection process. Please don’t roll your eyes though. This is a good thing! They make more than one type of car for a reason. Is a semi-trailer a better option for hauling supplies across country than a compact car? Of course! Having a lot of options in your anchor selection process can help you save a lot of time and money and the Hilti Kwik HUS Heavy Duty Screw anchor is one more way to do it.
(9/08/11)
Richard Vernon: You're not fooling anyone, Bender. The next screw that falls out will be you!
Breakfast Club (1985)
Joke:
Q: How many New Yorkers does it take to screw in a light bulb?
A: None of your damn business!
Baby Get your Head Screwed On, Cat Stevens, 1966
“Well if you’re feeling low, take it slow
Baby get your head screwed on”
Not too long ago, I was helping a contractor select a post installed anchor (PIA) to fasten a seismic wall tie to the bottom of a deck slab. Being the “frugal” person that I am, I recommended the most economical anchor I could find which was a 3/4” wedge anchor. After I put a lot of time into selecting this anchor, the field foreman asked me to change it because he wanted to use a screw anchor instead. I was surprised, so I asked him why he didn’t want to use the lowest cost anchor. He then reminded me that his guys would be installing thousands of these anchors and all of them overhead. To install a 3/4” wedge bolt overhead, with a large hammer, all day long was going to seriously slow down production. It was then that I remembered setting and testing 3/4” drop in anchors overhead myself. Not being built like Arnold Schwarzenegger, after the third or fourth 3/4”drop in anchor I could hardly lift my arm above my head! The foreman told me that the time he would save simply using an impact driver to set the anchor would easily outweigh the additional cost of the screw anchor (which was only minor to begin with). In fact he sold ME on the screw anchor from that moment on. Now, when I perform shear testing on anchor bolts, I always try to use a screw anchor to hold down my reaction frame. Screw anchors are easy to install and can be easily removed when you’re done.
Light duty screw anchors, or Tapcons, were first introduced by ITW/Redhead in 1975 but heavy duty screw anchors have just been available in the US since 2000. The newest heavy duty screw anchor to come to the market is the Hilti Kwik HUS (KH) and Kwik HUS-EZ (KH-EZ). Both anchors meet the requirements of AC 193, Acceptance Criteria for Mechanical Anchors in Concrete Elements and are approved for use with the latest International Building Codes. The main difference between the two anchors is the KH-EZ is approved for “cracked” and “uncracked” concrete where the KH is just approved for “uncracked” concrete. The KH-EZ also comes in a wider range of lengths and diameters than previous screw anchors, the smallest of which is 1/4 inch. So along with being approved for use in “cracked” concrete, this anchor should be a great help to designers who want to give contractors a range of choices for window and miscellaneous steel applications. Hilti has all of the technical information for these anchors on their website.
From my experience, here are the main reasons for using screw anchors:
Happy Anchoring!
Brian Clarke, PE
(5/18/11)
“Are you aware that I am rubber, and you are glue, and whatever you say to me bounces off, of me, and sticks to you? So put that in your, back pocket.”
Mary Katherine Gallagher (SNL):
~
The Big Bang Theory (2007)
[Leonard’s mother Beverly, a neuroscientist and psychiatrist, is visiting]
Sheldon Cooper: Your mother is brilliant, analytical, insightful - and I’m betting she never hit you with a Bible because you wouldn’t eat your Brussels sprouts.
Leonard Hofstadter: Sheldon, you don’t give your mother enough credit. She’s warm, she’s loving, she doesn’t glue electrodes to your head to measure your brain waves while potty training...
Sheldon Cooper: You were lucky! When I was a kid, if I wanted an EEG, I had to attach my own electrodes.
~
Looks like I picked the wrong week to quit sniffing glue.
Lloyd Bridges as Steve McCroskey , Airplane
~
Glue... very powerful stuff.
The Blues Brothers
Have you ever gotten knee deep in designing your rebar embedment depth with an epoxy when you realize that something’s just not right? You’re using the manufacturer’s technical information but the calculations don’t seem to work or seem unconservative? Let's go back in time a little bit.
Back in the 1960's a new way to design anchors in concrete after it had hardened had been developed. A Post-Installed Anchor (PIA) manufacturer came up with fast curing adhesives that could be used for doweling rebar. The adhesives were either pure epoxies, which are like glue, or hybrid adhesives, which are more like a mortar or paste. The technology and research for these adhesives are based on “anchor theory” which is great, but it has a few short comings. It is based on relatively shallow embedments and primarily deals with unreinforced concrete. But what happens when you’re doweling rebar? The current design code for post installed anchors only covers anchors embedded up to a maximum of 20xD or 25” (see ACI 318, Appendix D). This limits you to 12.5” for a #5 rebar... but a lap splice is usually longer than that… And what happens when you anchor into a column or pedestal? Edge distances become an issue in your calculations and what about the benefit to using stirrups and transverse reinforcement? How are you supposed to design this now?
Where you go now is back to rebar development length from good old ACI 318. What the anchor researchers found is after you get to a certain depth, your anchors behave differently. You’re less likely to have a concrete failure and more likely to have a steel failure. Development length of rebar in ACI 318 is based on yield strength and can lead to greater depths than anchor theory gives you. So how deep do you have to set that rebar in the concrete anyway? Let’s take a quick look at ACI 318-08, Chapter 12 for tension reinforcement…
The basic development length equation from Chapter 12 is:
Now let’s make a couple of assumptions:
f’c = 3,000 psi, fy=60,000 psi, db =#5 (5/8”), c = cover = 3”, rebar spacing = 6”, Ktr
(transverse reinf.) = 0,
Yt = 1.3 (more than 12” concrete below horizontal reinforcement), Ye = 1.0 (uncoated reinforcement), Ys = 0.8 (No. 6 bar or smaller), l = 1.0 (normal wt. conc.),
while (c+Ktr)/db < 2.5 & Yt *Ye<1.7.
A little math... (C+Ktr)/db = (3+0)/0.625 = 4.8 > 2.5, therefore use 2.5
Yt *Ye=1.3 < 1.7, therefore use 1.3.
Therefore, ld = 21.4”.
That is for rebar cast into concrete. Now let’s look at doweling with adhesives. What is the equation for yield strength of a rebar?
And the equation for bond strength? What is the depth/length required to develop the yield strength of the rebar? Setting Fy=Fb and solving for ld we get:
So what are we missing? Oh yeah, the bond strength, tbond. This is where it gets a little tricky. What is the bond strength of an adhesive? And what adhesive are you going to use? Nowadays the easiest place to find information about an adhesive is the Evaluation Services Report or ESR. This report can be found on the International Code Council’s (ICC’s) website http://www.icc-es.org/reports/index.cfm?search=search. If we look at Hilti’s HY-150MAX adhesive for #5 rebar at temperature range A, tbond = 1,296 psi (assuming the hole is the right size, it has been cleaned properly, etc.). So what is the depth of embedment required to develop the rebar yield strength?
For your design you would use the more conservative development length of 21.4”. BTW - this means that the bond strength used in the development length equation in Chapter 12 is less than the bond strength used in this example. The bond strength of a rebar embedded 21.4” with HY 150MAX is 54,456 lbs! (p*db*tbond *ld) which obviously will not be your failure mode. Please note that development length may not always control. Higher concrete strengths will reduce the development length per the ACI equation. For extra credit you can set ld for yield strength equal to ld from ACI 318 Chapter 12 and see exactly what bond strength is used… I know some of you will ;o)
Please note that your work is not done here. There are more checks throughout ACI 318-08 that need to be performed before you put your stamp on this. You may yet need to check for concrete breakout/anchor failure depending on your application. Ask yourself, are your rebar going into a pedestal, a column, top of wall or in a footing? Are your rebar in the tension or compression or in the positive or negative moment regions? There are many variables, so be careful and have someone back-check your work! For those of you that made it to the end of this article and have never gone down this path before, I thank you for your patience. Hopefully this article helps turn the light on and you can now see the rest of the way.
Happy anchoring!
Brian Clarke, PE
Digging a Little Deeper into
Powder Actuated Fasteners
(2/21/11)
“I can believe anything, as long as it is incredible.” ~ Oscar Wilde
“Skepticism is the beginning of Faith.” ~ Oscar Wilde
“My psychiatrist told me I was crazy and I said I want a second opinion. He said okay, you're ugly too.” ~ Rodney Dangerfield
As one of my favorite professors once said, “The best students are those who never quite believe their professors.” True enough. But he also said, “One ought not to reject the data merely because one does not like what the data implies.”
~Jim Collins, Good to Great
Being from NY I tend to be skeptical when I hear about something new... I attended a seminar on Powder Actuated Fasteners (PAF’s) used for fastening metal deck to bar joists while working for an A&E firm in Columbus, OH (Go Bucks!). I can’t say that I walked away from that seminar with too much regarding the technical aspects of the system. What I did remember was using a tool that would fire a nail into steel. It was really cool! You see, as a design engineer, you never got to put your hands on tools. Most people didn’t want you to! You were more likely to hurt yourself, or someone else, than actually do something good with it. It did make perfect sense that I attended the seminar though. The company I was working for was designing big boxes all over the country and this PAF system was faster than anything out there. But, I was old school and didn’t trust it. Seeing a few nails get shot into steel was not going to change my mind that quickly. Besides, nothing beats a good old puddle weld, right? And why change a good thing?
Well, that’s what I used to think. Then I worked for the company that invented the PAF and “mine eyes were opened”. Having previously been a structural engineering consultant for 10 years, one of my personal goals as a field engineer was to make the design engineer’s life easier. And this system seemed to fit the bill! I read and tried to learn everything I could about PAF’s. I found out how easy it was to install these fasteners and especially how safe it was. And speaking of safe, I’ve done a lot of work on my house and working with a reciprocating saw can be very dangerous! I’ve installed a lot of PAF’s and I would prefer working with them than using say a circular-saw any day of the week and twice on Sunday. Anyway, PAF tool uses a booster (gun powder) to create the driving energy. The energy from the booster is transferred into a piston which drives the fastener. There is a rubber buffer at the end of the tool that stops the piston and absorbs the excess energy. When the piston reaches the end of the tool the driving energy stops. The PAF is driven into the base material and the tool recycles. That’s the short version of the system.
So, can you really fire a nail into steel or concrete? The answer is a resounding YES! I was very fortunate to be able to test a lot of these fasteners in the field and I saw with my own eyes what they can hold. The capacity you can get out of these small fasteners is amazing. But, like all fasteners there are things to know that will make your life easier and your results much better. The most common application I saw was attaching light gage metal to steel.
There are many different types and sizes of PAF’s and selecting the right one is critical. Actually, selecting a few of the right ones is even better! To achieve the maximum capacity of the PAF, it should be installed with the head flush against the light gage metal.
[Please note, if you don't achieve precise installation don't worry! You still have capacity, just like any anchor or weld that is not 100%. You just may need to test a few to know exactly how much capacity you do have.]
If your base steel is 1/4" to 3/8” thick, it’s hard to mess up this installation. This is its wheelhouse! A 1/2” long PAF should penetrate perfectly and the tip will just dimple out the back side of the steel. Most of the problems that I saw in the field were installers trying to fasten into steel that was 1/2" thick or greater. I noticed a lot of engineers would choose a bigger PAF's than they needed to (“When in doubt make it stout” is the structural engineer's motto). This not something you want to do with PAF's though. When fastening to steel, 1/8" can make a big difference in performance. Trying to drive a larger/longer fastener into thick steel can get tricky. If there is not enough driving energy to push the PAF all the way through or the PAF is too long, you may have an “unbraced” length that can potentially buckle the shank. You could switch to a tool with greater driving energy but the shank might still break of the PAF is too wide. Also, the installers want to do exactly what’s on the drawings and assume the engineer selected the right PAF. So they try to make the PAF work. Sometimes they keep shooting PAF's until one sets right, but then you have a lot of wasted PAF’s and it may not look all that pretty. (FYI - A quick phone call to the right person, right now, would be a good idea. This is the time to ask questions, not when you’re done.) If the designer had selected a few PAF's of different lengths or just called out a holding capacity and let the installer find a PAF that worked best, getting the project compelte might go quicker and more smoothly.
I’ve found the best way to fasten to thick steel is to go with a narrower and shorter PAF and just use more of them. A smaller fastener, perfectly set, is as good as or better than a larger pin that does not penetrate as far as it should. It looks cleaner too! And since you’re not having the PAF shanks break on you, you actually use FEWER fasteners.
Things to remember:
- PAF’s are a great option when it comes to fastening to steel. They can save you a lot of time and money.
- The capacities are very high for such a small fastener
- The tool is easy to use (So easy, even an engineer can use it!).
- The PAF’s length and diameter are critical.
- Focus on the overall design capacity and don’t get locked into one particular PAF.
- Using more, smaller PAF’s may give you a much better job.
- The installer should set a few PAF’s at the start and make sure everything is looking good before finishing the job. (keep an eye on the piston for wear).
- And finally, when in doubt, ask a few questions to someone who knows the system well. It can make your life so much easier!
Happy Anchoring!
Brian Clarke, PE
Why do Post Installed Anchors Fail? (1/19/11) John Anderton: Why don't you cut the cute act, Danny boy, and tell me exactly what it is you're looking for? Minority Report, 2002 OK this quote might be a bit dramatic for an article about post installed anchors (PIA’s) but it is true none the less...and I just love that movie. In my last article titled “How to select the right PIA”, I mentioned how PIA’s were never taught in school. People learn what they learn along the way and do the best they can to understand them. When they need a PIA, a contractor, engineer or architect will most likely pick the anchor they are most familiar with. But old reliable may not be the right anchor because it was made with a particular application in mind. Your connections are critical and mistakes can be costly. So as the Grail Knight said in Indiana Jones and the Last Crusade (another great one!) “…choose wisely…” 12.2.1 Failure of the structural member in a shear-cone mode. 12.2.2 Failure of the structural member with or without cracking that radiates outward from the location of the anchorage device, resulting in a pullout of the anchor. 12.2.3 Pullout of the anchor. (This will only happen to mechanical anchors, BC) 12.2.4 Failure of the bond between the anchor and the structural member (This will only happen to adhesive anchors, BC). Displacement failure is evidenced by continuous displacement associated with a constant or decreasing applied load. 12.2.5 The fracture of any component of the anchoring device including hardware accessories shall constitute failure. Manufacturers test the heck out of their anchors and materials have become extremely reliable. When they say it should fail at a particular load, in a particular base material, it will pretty much fail that way. So if PIA’s are tested so much, and are so predictable, then why do they sometimes fail during testing? Here are the top 10 reasons from my experience that post installed anchors fail (in no particular order). Drum roll please… 1. The wrong anchor was selected for the particular base material. Wedge anchors are meant for concrete, not brick. A 6 inch sleeve anchor should not be used in 4 inch brick! The steel is too thick for the standard powder actuated fastener selected (asking it to go more than 1/2 inch is a big stretch). Know your anchor and the applications it was made for. Read the documentation from the manufacturer. Find out where it can and more importantly cannot be used. And finally, use common sense. 2. The person selecting the anchor thinks the capacity of the base material or the anchor is greater than it really is. You can’t get blood from a stone. Enough said.
Danny Witwer: Flaws.
John Anderton: There hasn't been a murder in 6 years. There's nothing wrong with the system, it is perfect.
Danny Witwer: [simultaneously] - perfect. I agree. But if there's a flaw, it's human. It always is.
Do you know why manufacturers offer lifetime warranties on their products? Is it out of the kindness in their hearts? It would be nice if that was totally true, but manufacturers know that they will get a reliable product almost every single time one comes off the assembly line. Why? Because the products are made by machines. When you input the correct information into a computer or a machine it will produce the same output every time. Machines don’t make mistakes, people do.
And what is the definition of “failure” anyway? The following is directly from ASTM E488 “Standard Test Method for Strength of Anchors in Concrete and Masonry Elements”.
3. A Hybrid adhesive meant for a hammer-drilled hole was used in a cored hole. It’s very interesting to see anchors pull out like popsicles but it is very costly. Epoxy adhesive anchors have a lower viscosity and can penetrate into the concrete unlike hybrid adhesives that rely on a rough hole for friction and micro-keying.
4. The holes drilled for adhesives were not cleaned properly. If there is dust in the hole, the adhesive will stick to the dust. Dust is not nearly as sticky as glue ;o) You need a brush! Most of the dust gets caked onto the side of the hole which is where it gets all of the bond capacity. Vacuuming the hole just cleans the bottom. Using a manual pump is cheaper, doesn’t need electric power and works better than a vacuum. Using compressed air is the best and is required for all adhesives used with ICC-Acceptance Criteria, AC 308, Acceptance Criteria for Post-Installed Adhesive in Concrete Elements.
5. The first few trigger pulls of adhesive were not discarded. When testing anchors at a site, I can always guess which anchor was installed first. If 3 anchors are installed with one cartridge of adhesive, if one fails, 9 out of 10 times it’s the first anchor installed. This is because the installer didn’t discard the first few trigger pulls. All two part adhesive anchors MUST discard the first few trigger pulls because it takes that many before the adhesive is properly mixed through the mixing nozzle. I know it may seem like waste but it’s less wasteful than cutting off the anchor and installing a new one… or god forbid someone gets hurt.
6. The mechanical anchor was not torqued enough. Torquing the expansion anchor causes the wedge shaped portion to slide up through the sleeve at the bottom. This expansion force creates the friction and micro-keying. If you don’t torque it enough your capacity will be less than you expect. (BTW - a small displacement is ok for these anchors).
7. The adhesive anchor was torqued too much. Most adhesive anchors are meant for two types of loadings. Tension and shear. Over-torquing the anchor can break the bond between the adhesive and the base material. Without the strong bond your capacity is greatly reduced.
8. The stone or brick pulls out from the wall. This is one failure mode that can get you in trouble. Anchors set and tested in brick should have a load bridge large enough to allow the brick or mortar to fail if it is the weakest link. If the bridge is too small it can appear that the anchors' load capacity is greater than it really is.
9. The adhesive was left out in the cold… or the heat! Some adhesives contain water. If the water is frozen or evaporates, it will not mix properly giving you interesting and very inconsistent results.
10. The tool being used to install powder actuated fasteners was not working properly. I’ve seen the pistons of these tools worn down to something unrecognizable. The pistons are like brakes in the car. The more you use them the sooner you need to replace them… and you need to replace them. The dimple at the top of the piston helps the fastener drive straight. If it takes you three shots to get one good fastener in, you need to replace the piston. You’ll waste much more in fasteners than the cost to replace the piston. Also, the residue from the booster builds up inside the tool and slows down the piston. This reduces the driving energy of the tool and may prevent proper penetration.
So the moral of the story is, when in doubt call someone who knows about the anchor and ask questions. Just tell them what you are installing and ask if you’re doing it right. If you ask the right person they will even give you some tips. Also, read the directions. I still do! There are so many different anchors and it’s hard to have everything committed to memory. Taking a few minutes to read the directions can save you a lot of time and money.
Happy Anchoring!
Brian Clarke, PE
When in Doubt? Test it!
(12/17/10)
"Back when I was in school, they never..." How cliché is that line, right? That saying was for "old" people, like people in their 30's! Well, I found there's something to be said for experience after all. Back when I was in school I never learned about post installed anchors (PIA's). So after I graduated, like every good engineer, I read! And asked a lot of questions from people who were around the block once or twice. But then I realized something. Those people were only telling me what they learned from the people they asked! This grapevine was good, but a fourth generation grapevine leaves a lot of room for error. My physics professor would have had a canary with the error propagation! The more I heard, the more conflicts I heard in opinions. I realized that I really didn't trust what people were telling me about PIA's at all. My license was on the line for crying out loud! And if I couldn't "prove" it, how could I trust it? So what did I do? I tested it...
And tested. There are a lot of different base materials in NYC you know. Yeah, there's concrete for starters. But then you have terra cotta, limestone, bedrock, brick of every origin, cmu, cinder blocks, cindercrete, ceramic tile... and oh yeah, steel! Do you think Hilti, Powers, and Simpson test for everything? It is not possible.
Getting back to PIA's. Are PIA's important? You betcha! Ask yourself this, "What is the glue (no pun intended) that is holding everything together?" Your connections! Connecting two similar materials is not a big deal. But two dissimilar materials? And old buildings in NYC that have been exposed to ice, snow and wind for hundreds of years... Not to mention water damage and fire (throw in a random tornado too while you’re at it). What kind of capacity can you expect?
Many anchorages, especially for architectural details, are overlooked. The structural engineer is focused on the big picture. The MEP engineers want everything to run smoothly. The architect is focused on the details that make the building unique (and there are A LOT of details!). Something weighing 50, 200, 1,000 pounds is not a huge load in the grand scheme of things. But when that load is hanging from the middle of your ceiling and 100's of people are walking past it every day, it better be secure.
Now some base materials will surprise you. Some old brick that looks like it would crumble in your hands will give you 1,000 lbs of tension with no problem. Some bedrock that you would think would give you 10,000 lbs easily, will only give you 4,000 lbs if you install it against the grain. And terra cotta? I've seen it hold everywhere from 100 lbs to over 5,000 lbs. Cindercrete will give you 2,000 additional pounds of tension capacity with the same diameter anchor, same embedment, same adhesive but a specialized helical anchor rod. There is no way to know exactly what you'll get unless you test it.
Testing it is easy (at least it should be) if you know what you're doing. It doesn't have to take a lot of time (if you plan, prepare and have the right equipment). And it can give you peace of mind knowing you are not guessing… (ahem) I mean estimating the anchor capacity. How do you know when you're guessing? You think about your design when you get home. You dream about a certain connection. It's like a splinter in your mind (like the Matrix). Something's not quite right but you're not sure exactly what it is.
I've had an engineer "assume" the capacity of an anchor set in a stone wall would be at least the minimum of a manufacturer’s allowable load using double the embedment depth and twice the diameter. He was right. The adhesive bonded brilliantly with the stone. And as I pulled the stone right out of the wall during a tension test, the realization that the mortar was like sand had finally occurred to him. Thankfully they were still in preliminary design. They chose to go another direction...
So the moral of the story is "Don't guess it, Test it".
Happy Anchoring!
Brian Clarke, PE
Top of Page
How to Select the Right
Post Installed Anchor (PIA)
(12/20/10)
Just a few years ago there were only two anchors that I used in my designs. One mechanical anchor and one adhesive. And both were typically used for attaching structural steel to concrete. If an architect would ask me to design an attachment for a piece of decorative steel, I would calculate the loads in accordance with the code, add any additional load that felt it needed and then rounded up! With that said, the loads for decorative pieces would still be pretty small. But I only had two choices! If the smallest mechanical anchor I liked was too big, oh well, so I'm a little conservative. I didn't have time to research all the possible anchors. I was comfortable using those two anchors so why change? Happy Anchoring!
Selecting the right post installed anchor (PIA) used to be easy. Grab your favorite anchor manufacturers' technical guide, open to the page that you've got tabbed, find the diameter that meets your load requirements, choose from list, and you're done. Today, due to the changing building codes and the many options available, it is much more important to know what you're doing. Make the wrong choice and it can cost you.
When PIA's became all I focused on I couldn't believe the selection. There were large anchors, small anchors, expansion anchors, undercut anchors, epoxy anchors, hybrid adhesive anchors, screw anchors, coil anchors, and impact anchors. So when do you use each type of anchor? Do you need them all? The answer is not always easy. However, the more you know the more economical you can be.
I always thought I was being helpful by specifying the faster curing adhesive anchors so I wouldn't delay construction. I later realized that I was making it impossible to install these anchors in 90 degree temperatures. Do you really want to specify a fast cure in the middle of the summer which gives the installer only 3 minutes to place the threaded rod in the hole? When an anchor bolt is missed and my GC had to core the hole, old reliable didn't work properly. Did you know that most hybrid adhesives need a hammer-drilled hole created by a carbide tipped bit to create a rough surface? Have you ever specified a wedge anchor (I didn't say sleeve anchor) in brick? Not a good idea. Speaking of sleeve anchors, have you ever tried to remove the bolt after the anchor is set? As you hammer in the anchor you beat up the threads (I didn't say wedge anchor) which makes it next to impossible to remove the nut. Leaving the nut raised 1/8" above the threads on this anchor will protect the threads and can save you a lot of time and headaches. Did you know screw anchors are great in CMU? Even if you catch a void that is not completely grouted solid you will still get some capacity from the threads biting into the face shell. And toggle bolts are a great low cost alternative to adhesives with screen tubes for interior terra cotta anchorages. They're great for hanging light ducts or electric conduits.
My advice is leaf through your technical guide to see all of your anchoring options. Leave it by your bed to help you fall asleep at night. There are some great anchors that you don't even know about. Also, what will that anchor experience over it's lifetime? Will it experience freeze-thaw, seismic loading, will it be exposed to the weather, or is being used for temporary construction or permanent? The anchor's Evaluation Services Report will tell you all about the testing that was done on the anchor. And then there's the changes to the building code (that's for another article)! Selecting the right anchor for your application just takes some patience, but you could bring down the costs of your connections significantly. When every dollar counts, this turns into an easy way to look good to your client.
Brian Clarke, PE
"The perfect blend of engineering design and construction reality"