Anchoring Methods

How is the above ground shelter anchored?

All our safe rooms must be appropriately anchored to a concrete slab that weighs at least two (2) cubic yards, has steel reinforcement, has wire or rebar, and is not severally cracked.

Typically, storm shelters are installed inside the house or in the garage. However, if the unit is installed outdoors, a new concrete slab must be poured before installing a safe room, following Torshel’s guidelines.

Talk Like An Engineer! 

Yes, let’s first learn a few critical terminologies to understand why Torshel’s units are capable of remaining attached to the slab even during an EF5 tornado.

 

What is Tension Force?

Tension is the force applied vertically to the anchor; let’s call it the “Pull Out” force. Therefore, a 3/4” x 4, 3/4” HILTI anchor inserted into a 3,000 PSI concrete slab will require a force of 6,250 lbs. to be taken out. If the concrete applied has a compressed strength of is 6,000 PSI, the tension force will be higher at 8,700 lb per anchor.

A medium-size safe room (4’W x 6’ L) requires 13 anchors; if installed on a standard 3,000 PSI, a 4” thick concrete slab will reach over 80,000 lbs. of Tension or “Pull Out” force. So even for an EF5 tornado, it is almost impossible to take it out.

What is Shear Force?

Without getting too technical and complicated for the understanding of those with little to no technical knowledge, Shear Forces are unaligned forces pushing one part of on object in one direction, and another part in the opposite direction.

How Does the Anchor Work?

Once the safe room is in place, we drill a 3/4” diameter x 4 3/4” deep hole. The hole is cleaned properly, and then the anchor is inserted inside with the aid of a hammer. At the bottom of the anchor, there is an expansion factor called “wedge”.  Afterward, a washer and a nut are placed onto the anchored by

applying 110 lbs of torque, the wedge will expand and lock the anchor inside the concrete. The anchor is not removable, unless the concrete is broken.

Standard Installation -Inside the house or in the garage

 For our smallest units up to 6’ x 6’ safe rooms

If your house was built up to construction codes, most likely it is 20’ W x 20’L or 24’x 24’, with a 4-inch thick foundation and made of 3,000 or 4,000 PSI concrete. Therefore, it has 5 to 7 cubic yards, each cubic yard weights 4,000 lbs, in other words, it has plenty of mass and weight to secure the unit thus exceeding FEMA guidelines of minimum 2 cubic yards.

During this anchoring option, Torshel will use HILTI expansion bolts 3/4” inch diameter by 4,3/4” inches length)- one every 12” (or Epoxy Anchors -5/8” in diameter x 4, 3/4” in length- one every 12”). Once installed, each bolt withstands 6,205 lbs of tension, and 12,200 lbs of Shear Force. Depending on the size of the shelter, the installation will require between 10 to 50 bolts.

Torshel’s “New Construction” Anchoring -The best in the industry

The standard option described above works great. However, if you are building a house you can get the best anchoring method in the market, which is described below. You must have this method for any 6’x 8’, 8’x10’ or bigger safe rooms.

Once you have assigned the location of your safe room, ask your homebuilder to pour concrete for a slab thickness of 12” (inches) and 2’ (feet) wider than the unit to be installed. For example, if the safe room is 4’W x 8’ L, the reinforcement concrete area will be 6’wide x 10’long, reinforced with rebar or wire. The shelter will be installed right in the center of the foundation. HILTI anchors will be installed every 12”, measuring 3/4” D x 10” L”. By following this method, the unit will double the tension and shear capacities.

The extra concrete and materials that your homebuilder will require will only cost approximately $150 extra.

Anchors cannot be placed while pouring the concrete; they must be installed after the shelter is set.

Outdoor Safe Rooms

Torshel or a local contractor can install safe rooms by following our guidelines. Build a 4,000-PSI concrete slab with footings (4) -each footing is 8” wide x 32”, one every 4’-5’. For example, if you order a large 4’ x 8’ safe room, the slab will be 8’ W x 12’ L x 12” H, with 12 core footings. For such a project, 5 cubic yards of concrete will be used (each cubic yard weights 4,000 lbs). The concrete itself will weight 20,0000 lb. During the anchoring, 3/4” x 10” HILTI anchors will be used every 12”. The bigger the safe room, the bigger the slab must be.

Epoxy vs Expansion Anchors 

Epoxy is an adhesive ideal for anchoring threaded rods, rebar and smooth to concrete. 

The following are pro and cons:

  1. Comparing the standard 3/4” x 4, 3/4” HILTI anchor against the 5/8” x 4” epoxy rod from HILTI, they both have the same Shear and Tension capacity,
  2. The epoxy adhesive needs an expensive “gun installer”, around $250, 
  3. The epoxy adhesive must be kept in stock for only a few days. Otherwise, it will be spoiled, 
  4. A professional installer must install the product to avoid improper application while the expansion anchors are easier to install
  5. However, if you want epoxy anchors Torshel can provide them for an extra fee.

Thank you for doing your research. Please, feel free to compare our anchoring methods with our competitors. Without a doubt, Torshel has one of the best ones in the world.