Simpson Strong-Tie LSTHD/STHD Strap-Tie Holdowns
This product is preferable to similar connectors due to easier installation, higher loads, lower installed cost, or a combination of these features. The STHD is an embedded strap-tie holdown offering high load capacity and a staggered nail pattern to help minimize splitting. It incorporates features that aid correct installation and improve performance.
Features
- The fastener pattern allows for fastening to the edges of double 2x's.
- Strap nail slots are countersunk to provide a lower nail head profile.
- Slots below the embedment line enable increased front-to-back concrete bond and help to reduce spalling.
- Rim joist (RJ) models accommodate up to a 17" clear span without any loss of strap nailing.
Material and Finish
- Material: LSTHD8, LSTHD8RJ are 14 gauge; all others are 12 gauge.
- Finish: Galvanized.
Installation
- Refer to Holdown and Tension Tie General Notes on pages 49-50.
- Use tables for both standard concrete and post-tension slab installations.
- Install before concrete pour with a StrapMate® or other holding device.
- Nail strap from the bottom up. Install strap plumb.
- 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.
- Do not install where 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. Also, do not install where 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 nailing.
- For installations in severe corrosion environments, refer to strongtie.com/cipcorrosion for additional considerations.
- See installation illustrations on page 60 for rebar information.
Two-Pour Installation for Downturn Footings
- For STHD10 installed through a 4"-thick slab, use the equivalent 8"-stemwall loads of the LSTHD8.
- For STHD14 installed through a 4"-thick slab, use the equivalent 8"-stemwall loads of the STHD10.
- For STHD14 installed through a 6"-thick slab, use the equivalent 8"-stemwall loads of the LSTHD8.
Codes
See page 11 for Code Reference Key Chart.
Allowable Tension Loads
Tables provide allowable tension loads for STHD installations based on concrete strength, seismic design category (SDC), and stud type (CFS).
| Model No. | Stemwall (in.) | Strap Length (L) (in.) | le (in.) | Required Nails | Uncracked | Cracked | Code Ref. | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Standard | Rim Joist | Standard | Rim Joist | Midwall | Corner | Endwall | Midwall | Corner | Endwall | ||||
| Wind and SDC A & B | |||||||||||||
| LSTHD8 | 185⁄8 | 321⁄8 | 8 | (20) | 8 | (20) #10 | 2,985 | 2,590 | 1,620 | 2,565 | 2,225 | 1,395 | 6 |
| LSTHD8RJ | 185⁄8 | 321⁄8 | 8 | (20) | 8 | (16) #10 | 2,985 | 2,590 | 2,135 | 2,565 | 2,225 | 1,835 | 8 |
| STHD10 | 245⁄8 | 381⁄8 | 10 | (24) | 10 | (24) #10 | 3,535 | 3,535 | 1,960 | 2,910 | 2,910 | 1,635 | IBC, FL |
| STHD10RJ | 245⁄8 | 381⁄8 | 10 | (24) | 10 | (22) #10 | 4,755 | 4,075 | 3,015 | 4,020 | 3,350 | 2,480 | |
| STHD14 | 261⁄8 | 395⁄8 | 14 | (30) | 14 | (30) #10 | 4,935 | 4,935 | 3,065 | 4,935 | 4,935 | 3,065 | IBC, FL |
| STHD14RJ | 261⁄8 | 395⁄8 | 14 | (30) | 14 | (30) #10 | 5,285 | 5,285 | 4,410 | 5,285 | 5,285 | 4,410 | |
| SDC C-F | |||||||||||||
| LSTHD8 | 185⁄8 | 321⁄8 | 8 | (16) | 8 | (16) #10 | 2,270 | 2,090 | 1,220 | 2,250 | 1,950 | 1,220 | 6 |
| LSTHD8RJ | 185⁄8 | 321⁄8 | 8 | (16) | 8 | (14) #10 | 2,615 | 2,125 | 1,635 | 2,250 | 1,950 | 1,610 | 8 |
| STHD10 | 245⁄8 | 381⁄8 | 10 | (18) | 10 | (20) #10 | 2,750 | 2,750 | 1,615 | 2,550 | 2,550 | 1,435 | IBC, FL |
| STHD10RJ | 245⁄8 | 381⁄8 | 10 | (18) | 10 | (20) #10 | 3,400 | 2,940 | 2,295 | 3,400 | 2,940 | 2,175 | |
| STHD14 | 261⁄8 | 395⁄8 | 14 | (22) | 14 | (24) #10 | 3,695 | 3,695 | 2,685 | 3,695 | 3,695 | 2,685 | IBC, FL |
| STHD14RJ | 261⁄8 | 395⁄8 | 14 | (22) | 14 | (24) #10 | 3,815 | 3,815 | 3,500 | 3,815 | 3,815 | 3,500 | |
Notes on Load Tables:
- Allowable loads have been increased for wind or earthquake loading with no further increase allowed. Reduce where other loads govern.
- Concrete shall have a minimum compressive strength of f'c = 2,500 psi.
- 0.148" x 3" or 0.148" x 2 1/2" nails may be used as a direct replacement for the required nails shown in the table with no load reduction when they are installed directly over framing or over 1/2" maximum structural sheathing.
- Use the number of nails listed in the table or as otherwise specified. In many cases, not all nail holes will be filled. Nail strap from the bottom up.
- Deflection at the highest allowable loads for installations over wood double studs is as follows: Installed on framing: LSTHD8 = 0.089", STHD10 = 0.117", and STHD14 = 0.118". Installed over 1/2" maximum structural sheathing: LSTHD8 = 0.114", STHD10 = 0.146", and STHD14 = 0.164".
- To obtain LRFD values, multiply ASD seismic load values by 1.43 and wind load values by 1.67.
- Per 2012, 2015, 2018 and 2021 IBC, Section 1613.1, detached one- and two-family dwellings in Seismic Design Category (SDC) C may use "Wind and SDC A&B" allowable loads.
- Minimum center-to-center spacing is three times the required embedment, 3 x le, for STHD strap-tie holdowns acting in tension simultaneously. Midwall installation is based on 1.5 x le end distance.
- See technical bulletin T-C-SCLCLM at strongtie.com for installation on structural composite lumber posts or columns.
- For brick ledge applications, use full loads shown for STHD14 installed in 8" stem wall.
- For slab-on-grade installation, use full loads shown for LSTHD/STHD installed in 8" stemwall.
- Fasteners: Nail dimensions are listed diameter by length. See pp. 21-22 for fastener information.
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.
Diagram Description: A diagram illustrates the Spall Reduction System, showing the STHD holdown with its built-in tab and the StrapMate locator line. It also shows the relationship between the holdown, shearwall diaphragm, framing nails, anchor bolts, and sill plate.
Installation Illustrations
Various illustrations show typical installation scenarios:
- Typical STHD14RJ Rim Joist Application: Depicts the holdown installed on a rim joist with clear span considerations.
- Single-Pour Rebar Installation: Shows a holdown embedded in a concrete foundation with rebar.
- Two-Pour Installation for Downturn Footings: Illustrates a holdown installed in a two-pour concrete foundation.
- Brick-Ledge Installation with Step: Shows the holdown installed on a brick ledge with a step.
- Brick-Ledge Installation Without Step: Shows the holdown installed on a brick ledge without a step.
- Spalling Load Reduction: Explains how bending the strap can lead to spalling and potential load reductions.
StrapMate® Strap Holder
The StrapMate is designed to keep the STHD and LSTHD straps vertically aligned during the concrete pour to minimize the possibility of spalling. The friction fit allows for quick and easy installation.
Features:
- The StrapMate is reusable.
- Works with STHD, LSTHD.
- Designed to fit 3/4" plywood forms up to 13/4" LVL forms and larger.
- The strap is positioned off the front edge of the form board.
Material:
Engineered composite plastic
| Model No. | Nails (in.) |
|---|---|
| SM1 | (2) 0.131 x 2 1/2 Duplex |
Diagram Description: An illustration shows the SM1 StrapMate Strap Holder, highlighting its design for holding the strap in place during concrete pours.
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