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.
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?
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.
Happy Anchoring!
Brian Clarke, PE