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Post-Tension Information

Technical & Installation Notes

This product is preferable to similar connectors because of a) easier installation, b) higher loads, c) lower installed cost, or a combination of these features.

The STHD is an embedded strap-tie holdown offering high-load capacity. The STHD incorporates many features that aid correct installation and improve performance. When installed on the forms with the StrapMate® strap holder, the unique design of the STHD delivers enhanced stability before and during the pour to help prevent both parallel and perpendicular movement (relative to the form). This results in accurate positioning of the strap and reduced possibility of spalling.

Features
  • The fastener pattern allows for fastening to the edges of back-to-back studs
  • Strap nail slots are countersunk to provide a lower nail head profile
  • The slots below the embedment line enable increased front-to-back concrete bond and help to reduce spalling
  • Rim joist models accommodate up to a 17" clear span without any loss of strap fastening

Material: LSTHD8, LSTHD8RJ — 14 gauge, all others — 12 gauge
Finish: Galvanized

Installation
  • Use all specified fasteners; see General Notes.
  • Use table below for both standard concrete and post-tension slab installations.
  • Install before concrete pour with a StrapMate or other holding device.
  • Fasten strap from the bottom up.
  • Strap may be bent one full cycle (bent horizontal 90° then bent vertical) to aid wall placement, but may cause spalling behind the strap. If the spall is 1" or less, measured from the embedment line to the bottom of the spall, full loads apply. 1" to 4" spalls for LSTHD8 achieve 0.9 times table loads. STHD10 and STHD14 achieve full load for spalls less than 4". Any portion of the strap left exposed should be protected against corrosion.
  • Other than where noted in the two-pour detail, do not install where: (a) a horizontal cold joint exists within the embedment depth between the slab and foundation wall or footing beneath, unless provisions are made to transfer the load, or the slab is designed to resist the load imposed by the anchor; or (b) slabs are poured over concrete block foundation walls.
  • Additional studs attached to the shearwall studs or post may be required by the designer for wall sheathing fastening.
  • For installation in severe corrosion environments, refer to strongtie.com/cipcorrosion for additional considerations.
STHD
STHD
Typical STHD14RJ Rim Joist Application
Typical STHD14RJ Rim Joist Application

Allowable Stress Design (ASD) Loads for STHD Strap Style Hold-Downs on CFS — 2,500 psi Concrete

Allowable Stress Design (ASD) Loads for STHD Strap Style Hold-Downs on CFS — 2,500 psi Concrete
  1. Deflection at highest allowable loads for install over CFS double studs are as follows: LSTHD8 = 0.065", STHD10 = 0.096" and STHD14 = 0.115".
  2. Multiply Seismic and Wind ASD load values by 1.4 or 1.67, respectively, to obtain LRFD capacities.
  3. Per 2012, 2015 and 2018 IBC Section 1613, detached one- and two- family dwellings assigned to Seismic Design Category (SDC) A, B or C are exempt from the seismic design provisions of IBC Section 1613. For this case, the allowable wind loads apply.
  4. Minimum center-to-center spacing is 3 times the required embedment (Smin = 3 x le) for STHD's acting in tension simultaneously. Midwall install is based on 1.5 x le end distance.
  5. See Fastening Systems for more information on Simpson Strong-Tie fasteners.
Typical STHD14 Corner Installation on Three Studs
Typical STHD14 Corner Installation on Three Studs
(end of wall similar)
Typical STHD14 Mid-Wall Installation
Typical STHD14 Mid-Wall Installation
Typical STHD End Installation
Typical STHD End Installation
Spalling Load Reduction
Spalling Load Reduction
If strap is bent horizontal 90° during installation, and then bent vertical for fastening to the stud, concrete spalling could result. Load reductions may apply, see installation note.
Single-Pour Rebar Installation
Single-Pour Rebar Installation
Maintain minimum rebar cover, per ACI-318 concrete code requirements
Two-Pour Installation for Downturn Footings
Two-Pour Installation for Downturn Footings

Spall Reduction System for STHD Holdown

Features
  • Built-in tab
  • StrapMate locator line
  • Additional diamond hole in RJ versions
Benefits

Built-in Tab:

  • Reduces spalling and costly retrofits.
  • No additional labor to install.
  • Holds STHD away from form board.

StrapMate Locator Line:

  • Easy inspection to ensure proper location.
  • Allows adjustment without removing STHD.

Additional Diamond Hole:

  • One more fastener to help prevent the STHD RJ models from bowing out at the rim joist section.