Engineering Selection of Holdowns and Foundation Anchorage for Wood-Frame Shear Walls
Reference Standards: ANSI/AWC NDS-2024 (National Design Specification for Wood Construction), ANSI/AWC SDPWS-2021 (Special Design Provisions for Wind and Seismic), ACI 318-25 (Building Code for Structural Concrete), ASCE/SEI 7-22 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures)
Technical Version: 1.2 (Verified March 2026)
This technical note provides a framework for structural engineers to select and specify overturning-restraint systems. A continuous tension load path from the shear wall chord to the foundation is mandatory per NDS-2024 §12.1 and SDPWS-2021 §4.3.6.3.1.
1. The "Weakest Link" Philosophy
The design capacity of an overturning connection is the lowest value of the following limit states:
- Wood Capacity: Net section rupture of the chord stud.
- Hardware Capacity: Published allowable load of the holdown body.
- Fastener Capacity: Shear capacity of the SDS screws or nails.
- Anchor Capacity (Steel): Tensile strength of the rod.
- Anchor Capacity (Concrete): Breakout or pull-out strength per ACI 318-25.
2. Shear Wall Overturning Mechanics
The design tension demand (T) is determined by the overturning moment. The fundamental equation is:
T = Vh / L
Where:
- V = Shear demand on the wall
- h = Wall height
- L = Wall length
Note: Engineers must also account for dead load stabilization (resisting moment) per ASCE/SEI 7-22 load combinations to determine the net uplift.
3. Phase 1: Holdown Selection (The Hardware)
Select hardware based on construction timing and seismic performance requirements.
Post-Installed Holdowns (Screw-Style)
SDS Heavy-Duty Connector screws preserve the net section of the chord stud by eliminating large bolt holes.
- HDUE Series (HDUE3 to HDUE17): The industry standard (direct HDU replacement). These feature a predeflected seat to minimize initial slip and control story drift.
- HDQ & HHDQ Series: For extra-heavy loads. The HDQ8 allows for raised installation (requires a bearing plate).
Cast-in-Place Holdowns (Embedded Straps)
Economical for new pours; they eliminate the need for anchor rods.
- LSTHD & STHD Series:
- LSTHD8 (14 ga): Light-duty/braced walls.
- STHD10/14 (12 ga): Engineered high-load walls.
- STHD-RJ Models: Feature extended straps to clear rim joists (up to 17" span).
- PA Purlin Anchors (PA23/28/35): Rated as strap-tie holdowns for chords to concrete/CMU.
4. Phase 2: Foundation Anchorage (Concrete Design)
The holdown's capacity is irrelevant if the anchor fails in the concrete. Anchor design must comply with ACI 318-25 Chapter 17.
Cast-in-Place (Preferred)
- SABR™ Series: (New in C-C-2026) The simplified, high-capacity replacement for SSTB and SB. Hot-forged with 6" threads to accommodate 2x or 3x sill plates.
- SSTB Series: Optimized proprietary bolts with offset heads to resist side-face blowout.
Post-Installed (Retrofit/Repair)
- SET-3G® Epoxy: Adhesive anchoring for high-capacity requirements in cracked concrete.
- Titen HD®: Mechanical screw anchor for light/medium loads.
5. Engineering Selection Matrix
| Demand Level | Holdown Family | Anchor Strategy | Critical Check |
|---|---|---|---|
| Light (<4k lbs) | LSTHD8 (14 ga) | SABR™ or Titen HD | Wood net section. |
| Medium (4k-10k) | STHD10 (12 ga) / HDUE7 | SABR™ or SSTB | Concrete edge distance. |
| Heavy (10k-20k) | STHD14 (12 ga) / HDUE13 | SABR™ or SSTB | Concrete breakout (ACI 318-25). |
| Extreme (>20k) | HHDQ14 / HDUE17 | SABR™ or SB | Mandatory breakout verification. |
6. Design Example: Drift and Failure Modes
Scenario: 8' x 4' shear wall, V = 2,000 lbs.
| Parameter | HDUE13 (Rigid) | STHD14 (Strap) |
|---|---|---|
| Anchor Slip (Δ_a) | 0.061" | 0.138" |
| Design Philosophy | Tension-Controlled (Ductile) | Elongation-Controlled (Flexible) |
Engineering Implication: The STHD14 introduces ≈ 2× more deflection than the HDUE13. In high-seismic zones, this may push total wall drift beyond allowable limits.
7. Quick Selection Workflow for Engineers
- Calculate Uplift: Determine T from shear wall analysis (SDPWS-2021).
- Select Holdown: Choose a model where allowable tension ≥ T (adjust for wood species, e.g., DF vs. SPF).
- Verify Anchor: Use SABR™ as the first choice; verify embedment, edge distance, and concrete strength (f'c).
- Confirm Drift: Include holdown elongation (Δ_a) in total wall deflection.
Engineering Automation: For rapid selection that integrates ACI 318-25 breakout checks with NDS wood design, use StructSuite. This module automates the iterative workflow, ensuring the foundation, hardware, and wood chords are synchronized for rapid plan check approval.
Disclaimer: Always refer to the latest Simpson Strong-Tie catalog (C-C-2026) and ICC-ES reports. Consult a licensed Professional Engineer for project-specific design.