This blog post will offer designers and installers several tips on properly detailing and installing inclined ASSY self-tapping screws in steel-to-wood connections, utilizing ICC-ESR approved 45-degree wedge washers. This post will provide a step-by-step solution to avoid common installation issues.
Approximately 8 minutes read.
What is the MTC Solutions 45-degree wedge washer?
The MTC Solutions 45-Degree Wedge Washer is an ICC-ESR approved cast iron washer, engineered for steel-to-wood connections with screws installed at 45-degrees. The wedge washer is available in three different sizes and is compatible with countersunk head screw types such as the ASSY Ecofast and ASSY VG CSK.
Why use the MTC Solutions 45-degree wedge washer?
Designing connections using inclined fully threaded screws with the MTC Solutions 45-degree wedge washer into a steel plate is a great way to develop a high capacity, high stiffness connection. Utilizing a wedge washer for inclined steel-to-wood screw connections eliminates the complex milling otherwise required to house the countersunk screw head in the steel plate. Furthermore, a thinner steel plate may be used, as there is no need for previously required extra thickness to house the screw head. These advantages lead to a more cost-effective steel-to-wood connection solution.
How to detail connections utilizing the MTC Solutions 45-degree wedge washer?
The designer detailing the steel plate connection must consider several different aspects of the steel plate geometry.
Steel plate thickness. The steel plate must be sized to conform with the minimum and maximum thicknesses according to the size of the 45-degree wedge washer used:
Slotted hole dimensions. The following table presents the design requirements based on screw diameter. More information and design considerations for coated plates can be found in the Structural Screw Design Guide.
Spacing requirement. The fasteners must meet the spacing requirement presented in the Structural Screw Design Guide. It must be noted that the spacing between two fasteners in a row shall be measured perpendicular to the screw axis, which results in larger spacing requirements at the surface of the wood member for inclined screws.
Additionally, it is recommended that designers specify drilling positioning holes on two opposite corners of the steel plate to allow the installer to achieve greater installation precision.
How to install the MTC Solutions 45-degree wedge washer?
Before we begin, the installer should utilize the proper tools and equipment. This includes:
The following video demonstrates good practice for the installation of ASSY VG CSK 5/16″ x 6-1/4″ screws at a 45-degree angle with the appropriate MTC 45-Degree Wedge Washer as outlined in the ICC ESR 3178.
Installation Step 1)Secure the steel plate’s position on the wood member. For these types of connections, alignment is crucial as the connection may be subject to high design loads and misalignment may result in reduced connection performance. For this reason, it is recommended that designers specify drilling positioning holes on two opposite corners of the plate. (In the installation video, the ASSY Ecofast 1/4” x 3-1/8” screw is used to hold the plate in position)
The steel plate is now ready for the installation of the 45-degree wedge washers and the inclined ASSY self-tapping screw.
Installation Step 2) This installation step is optional; however, it will ease the fastening process. Pre-drilling a pilot hole will aid in guiding the screw in the right direction and accelerate the wood bite process by the screw tip.
MTC Solutions’ installation accessory: The pre-drilling jig, as shown in the video, allows for simple and precise pilot hole drilling, which helps to mitigate misalignment.
After drilling the pilot holes, it is important to clear any saw dust or drill shavings created. It may seem trivial but saw dust can retain humidity which can damage steel connections over time. Removal is an easy task and a good habit to keep.
Installation Step 3) The final step is wedge washer and fastener installation.