HDA/HD Holdowns
Simpson Strong-Tie HDA/HD Holdowns are designed for seismic and high-wind applications, providing robust connections for wood-framed structures.
Product Overview
The HDA and HD series holdowns are self-jigging, simplifying installation and ensuring code-required minimum bolt diameter spacing. Their design accommodates various stud wall configurations, including standard 2x4 stud walls. Materials are typically galvanized, with options for Simpson gray paint or HDG (hot-dip galvanized) upon request.
Key Features and Installation Notes:
- Self-Jigging Design: Ensures proper bolt spacing for code compliance.
- Adjustable Seat Design: Allows for greater installation flexibility (HD6A, HD8A, HD10A, HD14A).
- Material: See table for specific material and gauge details.
- Loads: Refer to tables for allowable tension loads based on wood member thickness and species.
- Finish: Standard galvanized; HDG available.
- Fasteners: Use all specified fasteners. Consult General Notes for details.
- Engineered Wood: Contact manufacturers for connections not through the wide face.
- Anchor Bolts: Use steel nylon locking nuts or thread adhesive for improved connection. Bolt holes should be 1/32" to 1/16" larger than the bolt diameter.
- Washers: Generally not required between base plate and anchor nut, except for the HD15, which requires a standard washer on the anchor nut.
- Anchorage: Refer to Simpson's Anchoring Systems and Additional Anchorage Designs for options. Designer may specify alternate anchorage.
- Wood Member Spacing: Maintain minimum distance of seven bolt diameters from the end of the wood member. This is designed into the holdowns.
- Stud Bolts: Should be snugly tightened.
- Multiple Members: Designer must determine fasteners for joining multiple 2x members to act as one unit without splitting the wood.
- Retrofit Solutions: Refer to technical bulletin T-ANCHORSPEC.
- Codes: See page 12 for Code Reference Key Chart.
Installation Diagrams:
Typical HD5A Tie Between Floors: Illustrates the connection of a holdown to a wood member, showing threaded rod, floor joist, blocking, and the holdown base plate. It notes that BP (Bearing Plates) are required by the City of Los Angeles and advises checking local building codes. NDS Section 11.1.2.3 requirements for metal plates or washers are mentioned.
Vertical HD5A Installation with SSTB anchor bolt: Shows a holdown installed vertically with an anchor bolt. It specifies that washers are not required at the base.
Vertical HD15 Installation: Depicts a vertical installation of the HD15 holdown, indicating the need for washers under the anchor bolt nut and between the bolt nuts and wood.
HD10A (and similar models): A diagram shows the general form of the HD10A, HD6A, HD8A, and HD14A holdowns, highlighting dimensions like HB, SB, W, H, B, and SO. It also shows the connection to a stud and the anchor bolt.
HD2A installed as a lateral anchor for a deck guardrail post: Illustrates the HD2A used in a different application, referencing technical bulletin T-HD2AGRDRL for more information.
Vertical HD15 Installation: Shows the HD15 installed vertically, noting the stand-off providing minimum end distance to the end of the post from the post bolt.
Pressure-treated barrier: May be required, as indicated in a diagram.
For holdowns, per ASTM test standards: Anchor bolt nuts should be finger-tight plus 1/3 to 1/2 turn with a hand wrench. Care should be taken not to over-torque, and impact wrenches should not be used. Consideration for future wood shrinkage is advised.
Specifications and Load Tables
Detailed tables provide dimensions, material gauges, and fastener requirements for various HDA/HD models (HD2A, HD5A, HD6A, HD8A, HD10A, HD14A, HD15). These include Base Ga, Body Ga, Stud Ga, and dimensions like HB, SB, W, H, B, SO, Anchor Dia., and Machine Bolt Qty.
Allowable Tension Loads:
Tables list allowable tension loads for different wood member thicknesses (1 1/2" to 5 1/2") for various species groups (DF/SP and SPF/HF). These loads are based on NDS-2005 and include values for flush and raised installations, along with deflection data at the highest allowable design load.
Sources of Deflection at Shearwall Holdown Connections:
Several factors can contribute to deflection in shearwall holdown connections:
- Bolt slip at holdown stud bolts.
- Bolt slip due to oversized holes in the stud.
- Eccentricity when a holdown is installed on only one side of the stud.
- Anchor bolt nuts spinning loose during cyclic loading (mitigated by locking nuts or thread adhesive).
- Movement from insufficiently tightened nuts.
- Holdown deflection under load due to stresses from earthquakes or high winds.
- Lateral displacement of the wall rotating the stud, causing base plate displacement.
- Wood shrinkage affecting sill plates, rim joists, and top plates, potentially requiring retightening of nuts.
- Wood crushing at bolt bearing locations due to uplift forces.
- Wood crushing at the end of studs under normal loads, exacerbated by overturning forces during seismic or wind events.
Note: Diagrams illustrate potential deflection points and components like bearing plates, studs, sill plates, and foundations.
Product Availability
These products are available with additional corrosion protection. Contact Simpson for details on other available products with this option.
