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LDSS™ Light Diaphragm Spline Strap

The LDSS light diaphragm spline strap is designed to be placed directly on top of CLT (cross-laminated timber) and other mass timber panels to connect them together. Unlike plywood splines, the LDSS does not require routing. As part of the Simpson Strong-Tie® complete LDSS spline solution, the steel strap installs easily and safely using our PRO300SG2 Quik Drive® tool and collated Strong-Drive® WSV Subfloor screws. The LDSS features an innovative embossed hole design that helps guide the installation tool and increase fastener capacity.

Key Features

  • No routing required; the strap can be placed directly on top of mass timber panels, reducing manufacturing time and cost
  • Less susceptible to moisture damage than plywood splines, reducing need for expensive repairs
  • Embossed hole helps guide the installation tool into the hold and increases capacity per fastener
  • Tested for in-plane shear values
  • Can be used as part of a complete spline solution throughout a project for faster installation and to save on the total cost of spline connections


  • 18 gauge


  • Galvanized


  1. Place the strap on the surface of the panels with the centerline notches aligned with joint between adjacent panels.
  2. From a standing position, hold tool perpendicular to the face of the strap and place the noseclip over the embossed feature. Drive the screw. Repeat.
  3. Use all specified fasteners.


  • The LDSS has also been tested with 0.148" x 2 1/2" nails for specifiers or contractors who prefer a nailed connection. The embossed hole allows for the use of a power framing nailer using concentric, full round-head nails.

Related Literature

Product Information Table

Fastener Production Information and Stuff & Things
New products
Model No. Ga. Coating/Material Packaging Qty.
LDSS48 18 Zinc Galvanized, G90 1

Load Tables

Allowable Shear Loads

Model No. Ga. CLT Layup (min.) Fasteners Fastener Spacing (in.) Allowable Shear Load (lb./ft.) Slip Modulus γ (lb./in. per ft.)
Type Dimension Wind Seismic
LDSS48 18 Three-ply WSV #9 x 3" 4 1,030 1,030 1,030 1,030 17,050
2 2,225 2,225 2,225 2,225 34,090
Nails 0.148 x 2 1/2" 4 430 430 430 430 23,060
2 820 820 820 820 46,120
  1. Allowable loads are based on the use of cross-laminated timber (CLT) grades E1-E5 and V1-V5 material conforming to APA PRG-320. The allowable shear load applies to mass plywood panels (MPP) with equivalent S.G.
  2. Allowable loads have been adjusted for wind or seismic loading per 2021 SDPWS.
  3. Allowable loads are based on lesser of calculations per SDPWS 2021 or assembly tests.
  4. Fastener failure modes are Mode IIIs or Mode IV.
  5. Screws: SDS = Strong-Drive® SDS Heavy-Duty Connector Screws, model SDS25312; WSV = Strong-Drive WSV Subfloor screw, model WSV3S (collated for Quik Drive®).
  6. Nails: Nail dimension listed diameter by length.
  7. CLT panel thickness shall be adequate to accommodate full fastener length.
  8. The component of diaphragm deflection due to fastener slip at panel-to-panel joints calculated is calculated as, δf = CLen, where,
     C = (1/PL+1/Pw)/2
     PL = Length of individual CLT panel (ft.)
     Pw = Width of individual CLT panel (ft.)
     L = Overall length of diaphragm (ft.)
     en = Design load per foot (lbs/ft) / Slip Modulus, γ (lb./in per ft)
    (Reference — Applied Technology Council. 1981. Guidelines for the design of horizontal wood diaphragms. Redwood City, CA.)
  9. For steel splines, the AISI calculated allowable shear capacity of the steel exceeds the reported allowable shear loads by at least a factor of 2.0, satisfying the requirement of SDPWS 2021 Section 4.5.4(3)
  10. For additional information on fastener slip and stiffness/slip modulus, see:
    1. American Wood Council. 2018. ANSI/AWC National Design Specification® for Wood Construction, NDS®, Section 11.3.6. AWC, Leesburg, VA.
    2. Zhan, J.J. 1991. Design Equation for Multiple-Fastener Wood Connections. US Forest Service, Forest Products Laboratory, Madison, WI.

Code Reports & Compliance