“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 complete 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!
Brian Clarke, PE