Today’s blog post is the first in a series called “Anchor Anatomy 101.” Each post is designed to clarify anchor components, installation processes, and common applications to help you make informed anchor selection decisions based on your project’s unique requirements.  

Concrete and masonry screw anchors are selected by designers and contractors for their load-carrying capacities, versatility, and ease of installation. In addition, screw anchors like the Simpson Strong-Tie Titen HD® series have obtained evaluation reports, published by ICC-ES and IAPMO-UES, which building officials reference during the approval process. Understanding screw anchor anatomy helps you select the best anchor type. Let’s take a closer look at the anchor anatomy of the Titen HD® (THD) concrete and masonry screw anchor starting from the head moving down to the leading tip as shown in Figure 1. 

1. Head: THD screw anchor heads come in various styles such as hex-washer, countersunk, flat-washer, and internally threaded as shown in Figure 2. Head selection is highly dependent on the application and fixture. For example, a wood sill plate may use a hex-washer head whereas a 2x wall ledger may require a flush mounted flat-washer head to avoid conflict with the joist framing into it. The internally threaded THD rod coupler with extended hex washer head is used to anchor Strong-Rod® anchor tiedown systems (ATS) and uplift restraint systems (URS).

2. Shank: The THD screw anchor shank includes both an unthreaded section and threaded section which extends for the length of the screw body. The length of the unthreaded section of the shank varies. The total shank length ranges from a minimum of 1 7/8″ to a maximum of 15″. The unthreaded section provides stability and prevents over-torquing during installation. 

3. Coating: Carbon-steel THD screw anchors are manufactured with two types of coatings. Either an electrodeposited coating of zinc, with a minimum thickness of 0.0002″(5 μm) in accordance with ASTM B633, SC1, Type III or mechanically galvanized in accordance with ASTM B695, Class 65, Type I. The zinc-plated coating is for dry, interior applications. The mechanically galvanized THD is permitted for exterior exposure or damp environments, and for interior locations where anchors are in contact with preservative-treated and fire-retardant-treated wood. For coastal conditions or chemical exposure, the Type 304 or 316 stainless steel THD is recommended (see Figure 3). 

4. Screw Body Threads: The helical-coil shaped cutting threads along the length of the THD’s body are critical for load resistance performance. During installation, they undercut the concrete or masonry substrate, which develops a mechanical interlock between the screw anchor threads and the base material. The threads efficiently engage and transfer the load from the screw anchor to the concrete or masonry base materials. 

5. Screw Body: The main screw anchor component is made of either solid carbon or Type 300 Series stainless steel (304 or 316). The heat-treated carbon steel or stainless-steel screw body diameters are available in 1/4″ up to 3/4″. Overall screw body length, including the shank, ranges from 1 3/4″ to 15″. The tensile strengths are diameter and material dependent and range from 104,000 psi to 125,000 psi. 

6. Leading Tip: The tapered tip with leading hardened carbon-steel, helical-coil, serrated threads is designed to facilitate the initial penetration into the concrete or masonry substrates (see Figure 3). A specialized heat-treating process creates tip hardness for better cutting and reduced torque during installation. The leading serrated carbon-steel threads on the tip of the THD undercut the concrete as the anchor is driven into the hole, making way for the rest of the threads to interlock with the concrete. The first couple of cutting threads on the stainless-steel THD anchors consist of carbon steel that are hardened and brazed onto the tip of the anchor. Some hardened fasteners may experience premature brittle failure if exposed to moisture due to a phenomenon called hydrogen-assisted stress corrosion cracking (HASCC). The THD anchors have been evaluated for reliability against HASCC, and they haven’t been found significantly sensitive to the stress-induced hydrogen embrittlement phenomena.

Installation Process for concrete, concrete on metal deck, and masonry base materials (See Figure 4)

1. Drill: THD installation starts with drilling a pilot hole using a rotary hammer drill with a standard carbidetipped drill bit (ANSI B212.15). The THD pilot drill hole diameter is to be equal to the nominal anchor diameter. The hole is drilled to the specified nominal embedment depth plus an additional over-drill amount. The minimum over-drill depths are diameter dependent and range from 1/8″ for the smallest diameter up to 3/4″ for the largest diameter. Over-drilling allows the drill dust created during installation to settle to the bottom of the hole.

2. Clean: The hole is then blown clean of dust and debris with oil-free compressed air . This step is recommended but not required for overhead holes. Optionally, if the concrete element is thick enough, deeper over-drill holes may be drilled, allowing the drill hole dust and debris to settle to the bottom of the hole in lieu of using compressed air.

3. Install: The THD is inserted into the fixture first and then into the drilled hole. Using a manual socket or
impact driver, the THD anchor is driven into the base material until the underside of the washer head contacts the fixture. THD screw anchors do not require a specific torque to be set properly. Note, the recommended steel fixture hole size is 1/8″ to 3/16″ larger than the THD anchor diameter. The larger hole size in the steel fixture allows the threaded section of the THD to pass through it without making contact.

Typical Screw Anchor Applications

Screw anchors are used in a variety of heavy-duty and light-duty applications, from securing structural elements to mounting window or door frames or mechanical, electrical, and plumbing (MEP) components. They can be installed vertically and horizontally to resist uplift, shear, and tension loads. The example anchorage applications in Table 1 and Figure 5 highlight just a few of the many THD anchorage applications across several industries.

Conclusion
Using your newfound knowledge of the anatomy, installation, and typical project applications of the Titen HD® post-installed concrete and masonry screw anchors, you can confidently select, design, and specify the best type
to meet your projects challenges. Stay tuned for the next Anchor Anatomy 101 blog post featuring adhesive anchoring systems. Please contact your local Simpson Strong-Tie field engineer for any of your anchoring product or project application questions.