Design Simpson Strong-Tie Screws to the NDS

Simpson Strong-Tie is a US manufacturer of structural fasteners and connectors, with a broad Strong-Drive line of self-drilling wood screws. In the US, their screws are recognized under several evaluation reports: ICC-ES ESR-3046, ESR-2236 and ESR-1472, and IAPMO-UES ER-192 and ER-262, which publish reference design values for use with the ANSI/AWC NDS under the IBC and IRC. SPEC Toolbox designs the screws using those values, in both ASD and LRFD.

The US integration follows the Simpson Strong-Tie US database, grouped by role. Each family is backed by the evaluation report noted.

Partially threaded

• SDWS Timber washer head and SDWH Timber-Hex hex washer head, for wood-to-wood and steel-to-wood connections (ER-192).
• SDCP countersinking head and SDHR large hex head, heavier structural and connector screws (ESR-3046).
• SDS, a 1/4 in. hex-washer-head heavy-duty connector screw (ESR-2236).

Fully threaded

• SDCF countersinking head and SDCFC cylinder head, in lengths beyond three feet for deep laminations (ESR-3046).
• SDWC cap head, a truss screw (ER-262).

Subfloor and sole-plate

• WSV subfloor and diaphragm screw (ESR-1472), and SDWV sole-to-rim screw (ER-192).

Double-thread

• SWD double-threaded screw (ER-262)

Screws are offered in zinc, mechanically galvanized, hot-dip galvanized, Double Barrier and Type 316 stainless finishes. Diameters and lengths are as listed in the reports.

At a glance, in the US, Simpson Strong-Tie families support:

• Wood-to-wood and steel-to-wood connections, with steel side members.
• Sawn lumber, structural glued laminated timber, structural composite lumber (LVL, PSL, LSL), and the face of CLT.
• Withdrawal, head pull-through and lateral loading, and combined lateral-plus-withdrawal, per the NDS.
• Both ASD (allowable) and LRFD (design) methods.
• Dry service, with zinc, galvanized, Double Barrier and stainless corrosion options.

• Steel-to-wood as well as wood-to-wood. Many families carry tabulated steel-to-wood lateral values, with steel side members at a minimum tensile strength of 45 ksi, including light-gauge steel for connector applications.
• Structural composite lumber and CLT in scope. Alongside sawn lumber and glulam, the reports cover structural composite lumber (LVL, PSL and LSL) and the face of CLT.
• Very large fully threaded screws. The SDCF and SDCFC families reach lengths beyond three feet, for deep laminations and mass-timber assemblies.
• Broad corrosion range. Beyond zinc, the line includes mechanically and hot-dip galvanized, Double Barrier and Type 316 stainless options, for treated-wood use within each report’s exposure conditions.

The Simpson Strong-Tie US screws are available in the Screw module and in the connection detail calculators, worked in ASD or LRFD to the NDS:

• panel-to-panel joints (half-lap and spline);
• slab-to-wall, wall-to-wall and floor-to-wall.

Reference values are selected for the assigned specific gravity of the connected members, and end, edge and spacing requirements are applied per the NDS and the report geometry, including the separate predrilled and non-predrilled cases and the larger distances required in denser species such as Douglas fir.

Design follows the ANSI/AWC NDS under the IBC and IRC. The Simpson families are backed by ICC-ES ESR-3046, ESR-2236 and ESR-1472 and by IAPMO-UES ER-192 and ER-262, each publishing reference (allowable) design values in imperial units for withdrawal, head pull-through and lateral resistance; several also publish LRFD fastener strengths directly. Reference values are adjusted by the applicable NDS factors for the chosen method, among them load duration, wet service, temperature, group action, geometry and end grain, to give allowable (ASD) or design (LRFD) values. Reference values are keyed to the member’s assigned specific gravity (with lateral design limited to a specific gravity of 0.55 or less), and steel side members are designed per AISI S100 or AISC 360. The evaluation is for dry service; carbon-steel screws in saltwater exposure, and lateral design with inclined fasteners, are outside scope. The screws were also shown to comply with the City of Los Angeles code and the 2023 Florida Building Code, Building and Residential, including its High-Velocity Hurricane Zone provisions, through the reports’ supplements.