If you&#;ve ever seen a crane lift warehouse walls into place or a truck tow a 20-foot precast panel through town, you&#;ve witnessed first-hand the modern marvel that is concrete construction.
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But you rarely see a work crew install the anchors and fastening systems that hold concrete buildings together.
What types of fasteners do we use in commercial construction to keep multistory concrete buildings sturdy and stable?
To name a few:
Screws.
Bolts and sleeves.
Wedges and lag shields.
Below, we&#;ll talk about the most common types of concrete-fastening systems used in the construction industry.
Concrete is a special material that is more difficult to work with than other materials.
As opposed to drilling a screw into wood or bolting two pieces of metal together, fastening to concrete requires a certain finesse and specialized anchors.
This process involves three steps:
The last step is where the magic happens. When you insert the fastener into the anchor, it causes the anchor to expand and grip the sides of the hole.
We&#;ll discuss the various types of masonry fasteners later, but here&#;s a video demonstrating how wedge anchors work to give you an idea of what fasteners look like.
While all anchors must expand to work, there are two different types of expansion anchors.
The first is a pre-expanded anchor, like the split drive anchor, which expands as you install it.
Unexpanded anchors, such as the machine screw anchor, do not expand on their own. They need to be set after installation.
Of course, this process requires precision to work. You need the perfect hole size and embedment depth for the masonry anchor to hold.
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When concrete anchors are installed correctly, they can support a lot of weight. Heavy-duty anchors (the type used in commercial construction) can support wall-hung objects weighing over 200 pounds.
However, several factors can impact a fastener&#;s strength:
A fastener&#;s strength also varies if you&#;re mounting to a ceiling, wall, or floor. Suspended objects require stronger anchors, as they have nothing supporting them from underneath.
Luckily, there is also a wide selection of anchors to choose from, each with its own unique features that work for specific concrete construction projects.
Let&#;s look at each of these more closely.
Photo: Confast
Machine screw anchors are a type of unexpanded anchor. There are eight different diameters of machine screw anchors to choose from.
To use these anchors, you will need the following equipment:
The installation process has five steps:
One of the best reasons to use this type of anchor is that you can remove the fixture later if necessary. Simply unscrew the bolt or screw to detach the fixture.
One downfall of this type of anchor is that it is made from Zamac, a highly corrosive zinc alloy.
This type of anchor works with just about any base material, including mortar and stone, but it cannot bear heavy loads.
Photo: Grainger
This anchor is similar to the machine screw anchor but requires a lag screw instead of a machine screw. It also requires no setting tool.
These anchors are cylindrical sleeves with a rib on the exterior that cuts into the base material when expanded.
Lag shields are one of the best anchors you can use in a situation where they may be subjected to vibration.
Lag shields come in six different diameters, both long and short.
Here is the four-step process of installing a lag shield:
Again, similar to machine screw anchors, this type of anchor keeps the fixture removable. All you need to do to remove the fixture is remove the lag screw.
Photo: City Mill
Strike anchors are male anchors used to attach lightweight fixtures. They are made from steel coated in yellow zinc.
These anchors require no tools for installation and come packaged with a heavy-duty fastener, nut, and washer.
They are also known as hammer drive pin anchors or hammer set anchors. They come in many different sizes and lengths.
The installation of these anchors requires six steps:
Photo: Dixon Electric
Plastic anchors are used in both drywall and concrete. These small anchors are meant for light-duty projects and won&#;t hold heavy fixtures.
These anchors are inserted into predrilled holes, then a screw or nail is inserted into the anchor.
Related: What&#;s the Difference Between Cement and Concrete?
Photo: Confast
Wedge anchors are one of the strongest anchors available. They come in nine different diameters and several different lengths.
The larger the anchor, the more holding power it has.
They also come in several different materials, so you can use them in areas with or without the possibility of corrosion. These include carbon steel, 304 stainless steel, and 316 stainless steel.
304 stainless steel is suitable for areas with moisture and water present, but 316 stainless steel can withstand chemicals and water submersion.
If your concrete is damaged or at high risk of cracking, look into ITW Red Head Trubolt concrete wedges. This specialized product is approved for use in cracked concrete and seismic areas. It comes zinc-plated for indoor use.
Follow the manufacturer&#;s installation instructions here.
Photo: ASMC
This anchor is a threaded bolt covered by a metal sleeve with a nut and washer connected to one end.
You can find them with a few different types of bolt heads:
Sleeve anchors come either zinc-plated or in 304 stainless steel.
There are six steps to installing a sleeve anchor:
Photo: Grainger
These anchors are only to be used in solid concrete and require a setting tool for installation.
As the name implies, this anchor is dropped into a predrilled hole and set to expand.
It is a &#;female&#; anchor often used to hang threaded rods from ceilings to hold electrical cables, HVAC ductwork, or fire sprinklers.
Drop-in anchors come in five different diameters in zinc-plated steel, 304 stainless steel, or 316 stainless steel.
These anchors have a five-step installation process:
Photo: MSC Industrial Supply
To use a threaded rod as an anchor, you need to drill a hole in the concrete and fill that hole with epoxy.
Place the threaded rod or rebar into the hole and leave it to cure. The curing time depends on the specific type of epoxy used.
Photo: Confast
This anchor is simple to use. It resembles a bloated pin and comes with either a flat or round head.
They come in one diameter, quarter-inch, but in different lengths. It is considered a pre-expanded anchor since the split base applies constant pressure against the side of the hole.
To install, simply drill a quarter-inch hole into the concrete. Lay the fixture over the hole, then insert the anchor through the fixture and tap it into place with a hammer.
Photo: Grainger
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These concrete fasteners differ from the other types in that they come in one piece; the anchor is actually built in.
Concrete screws resemble traditional screws, although they have coarser threads.
These screws are often referred to as self-drilling or self-tapping screws because they tap their own threads when inserted into a predrilled hole.
Tapcon is well known for its blue concrete screws. They come with either a hex head or a star head.
Some concrete anchors are made for light-duty fastening, while others are made for medium-duty or heavy-duty jobs.
You should consider a few factors to determine which are best for your situation.
For instance, you should think about the potential for corrosion.
If your job site is indoors and dry, zinc-plated anchors will do just fine.
However, if your project is outdoors or underwater, it is imperative to use stainless steel anchors, or they will rust, and you will lose holding strength.
You also need to find the right anchors for your base material.
The chart below can give you an idea of the types of anchors we discussed and how they are best used. They are listed from strongest to weakest.
The X&#;s mean the anchors are suitable for the materials, while the O&#;s mean they can be suitable in certain situations. A dash means the anchor is not suitable for the material under any circumstances.
Solid ConcreteHollow BlockFilled BlockStoneBrickMortarThreaded Rod AnchorX
&#;&#;&#;&#;&#;Wedge AnchorX
&#;O
O
O
O
Sleeve AnchorX
X
X
X
X
X
Drop-In AnchorX
&#;O
O
O
O
Split DriveX
O
X
X
X
X
Lag ShieldX
X
X
X
X
X
Concrete ScrewsX
O
X
X
X
X
Strike AnchorX
O
X
X
X
X
Machine Screw Anchor
X
&#;X
X
X
X
Plastic AnchorX
X
X
X
X
X
This selection guide is also very helpful for understanding the different types and methods for connecting concrete.
Note: Steel rebar is used to strengthen solid concrete and can improve any anchor&#;s holding power. Rebar is used in every large-scale concrete construction project.
Unlike drywall anchors, concrete anchors can&#;t fasten to a wall behind the base material. This means the anchor itself must do all the holding.
When installed with precision, it&#;s amazing how much holding power a small concrete anchor can have.
Welcome to the marvel of modern construction and engineering!
Those who apply the correct technique can build strong and reliable concrete buildings.
Don&#;t forget to call FMP if you need a commercial contractor in Colorado!
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