Does the use of lag screws with shear plates affect installation?
Shear plates are designed to be installed with standard
machine bolts and nuts, but they can also be used with lag screws. One
thing to take into consideration is how the use of lag screws affects
installation. When installing lag screws, you need to drill a pilot hole
to prevent the head from breaking (Lag
Screw Pilot Hole Diameters). This causes an issue when installing
shear plates because the size of the pilot hole for lag screws is different
than the hole drilled for bolts.
For example, The use of a 4” x ¾ dapping tool requires a 13/16” pilot hole, but the pilot hole for a ¾” lag screw is ½”.
Section 22.214.171.124 of the American Wood Council’s National
Design Specification for Wood Construction reads as follows:
“Where lag screws are used in place of bolts, the hole for
the unthreaded shank shall be the same diameter as the shank. The
diameter of the hole for the threaded portion of the lag screw shall be
approximately 70% of the shank diameter”
For example, if you have a ¾” x 12” lag screw with standard
6” thread length, you would drill a 12” deep pilot hole ½” in diameter then
re-drill the top 6” of the hole 3/4” for the shank of the screw. However,
the pilot bit on the grooving/dapping tools is 13/16” in diameter.
Therefore, you will need to check with your engineer to determine if the top
portion of the pilot hole can be drilled large enough to accommodate the 13/16”
pilot bit or if you will need a custom pilot bit made that will fit into the ¾”
Can I use pitch diameter bolts with shear plates?
Often bolts 10” and longer are made with reduced bodies and full size threads. These are bolts where the unthreaded shank is equal to the pitch dimeter of the threads and the threaded portion is equal to the nominal diameter. This is allowable per ASME B18.2.1 dimensional tolerances and ASTM A307 Grade A hex bolts. However, The American Wood Council does not allow this when used in conjunction with shear plates. In section 126.96.36.199 of the 2015 National Design Specification for Wood Construction, it says, “Bolts used with … shear plate connectors … shall have an unreduced nominal or shank (body) diameter in accordance with ANSI/ASME Standard B18.2.1.” If you are going to use reduced body bolts, you will want to confirm with the project engineer that this is allowable.
Can roll threaded bolts with a reduced body diameter be used with shear plate timber connectors?
No. According to Section 188.8.131.52 of the American Wood Council’s National Design Specification for Wood Construction, a bolt with a full body diameter must be used with shear plates.
184.108.40.206 Bolts used with split ring and shear plate connectors shall conform to 11.1.3. The bolt shall have an unreduced nominal or shank (body) diameter in accordance with ANSI/ASME Standard B18.2.1 (Reference 7).
Why do split ring grooving tools and shear plate dapping tools cost several hundred dollars each?
We often have customers ask why the installation tools are so expensive compared to the shear plates and split rings. Shear plates and split rings are not easily installed (correctly) without using the designated installation tools. They are engineered tools weighting 5.5 pounds each made with high strength tool steel blades designed to cut a precise groove or dap in wood. The cutting blades are both able to be sharpened and replaced, which can extend the life of the tool indefinitely if properly maintained. Tens of thousands of shear plates and split rings can be installed over the lifetime of a single tool.
What is a shear plate?
According to ASTM D5933, the specification covering shear plate timber connectors, they are, “Round, cast, or stamped disk-like load-transfer devices having a flat base and a perimeter bearing rim protruding in one direction normal to the base, with a hole passing though the center of the disk to accommodate an attachment bolt or lag screw.” Shear plates increase the strength of the joints in timber construction by providing a large area for the surrounding timber to bear against. This eliminates the small bearing area provided by a bolt, and enables the stresses to be distributed over practically the entire cross section of the timbers involved.
Do I need to use a dapping tool to properly install a shear plate?
Yes. Although the dapping tools are by no means inexpensive, they are a necessity when it comes to properly installing shear plates.
Is a drill bit sold with the dapping tool?
No. Up until the late ’90s, or thereabout, dapping tools were sold with a drill bit. The drill bit was attached to the cutter head and the dap was created in the wood at the same time the hole was being drilled. The design has since changed, and daps are now created in a two part process in which the hole is drilled first, and the dap is created by inserting the pilot bit into the predrilled hole. Any standard drill bit purchased at a local hardware store should work for drilling the bolt holes.
Are shear plates domestically manufactured or imported?
Both. It is unlikely that your construction project will require domestic shear plates, but if it does, both are available. There is no difference between the quality of a domestic and imported shear plate as both products are manufactured to meet the requirements of ASTM D5933. If your project is a federally funded highway job or military project of some sort, you may need domestic shear plates. However, in most instances, there will not be a domestic requirement and imported shear plates are far more economical. Refer to this FAQ on Portland Bolt’s website for more information on domestic requirements on construction projects.
Are there any specifications covering shear plates?
ASTM D5933 and ASTM A47 grade 32510 cover shear plate timber connectors. ASTM A153 covers the galvanizing of shear plates.
What are shear plates made out of?
4″ shear plates are cast iron, while 2-5/8″ shear plates can be either cast iron or pressed steel.