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MDSS Medium Diaphragm Spline Strap

The MDSS96 surface spline is 95 1/2" long, is attached with Strong-Drive® SDS Heavy-Duty Connector screws and is an ideal solution for CLT diaphragms. For CLT manufacturers, it reduces costs by eliminating or reducing time for milling at panel edges. And since our tabulated values are based on tests, not just calculations, Designers can value-engineer a solution using fewer screws than calculated solutions would allow.

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
  • Tested for in-plane shear values


  • 14 ga.


  • Galvanized (G90)


  • Use all specified fasteners
  • Fasteners may be installed with the Timber Drive™ Structural Screw Fastening System

Related Literature

Product Information Table

Fastener Production Information and Stuff & Things
Model No. Ga. Coating/Material Packaging Qty.
MDSS96 14 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
MDSS96 14 Three-ply SDS 1/4" x 3 1/2" 8 1,420 845 1,015 725 24,110
6 1,670 990 1,350 965 32,140
4 2,450 1,685 2,025 1,445 48,210
  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 is calculated as,
    δf = CLen
    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)
  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. 9 pp.0

Code Reports & Compliance