General Notes for Straps and Ties
These general notes are provided to ensure proper installation of Simpson Strong-Tie straps and ties.
- The (160) loads have been increased for wind or earthquake loading, with no further increase allowed. Reduce where other loads govern.
- When installing strap over 5/8" maximum wood structural panel sheathing, use 2 1/2"-long nails minimum.
- SD screws are Simpson Strong-Tie® Strong-Drive® SD Connector screws. See Fastener Types and Sizes Specified for Simpson Strong-Tie Connectors.
- For straight straps in tension, use half of the fasteners in each member being connected to achieve the listed loads.
- Tension loads apply for uplift when installed vertically.
- Field-bending straps is not recommended unless otherwise noted.
- If wood splitting is a concern, consider spacing the nails at every other location.
- The cut length of coil strap shall be equal to twice the “end length” noted in the tables plus the clear-span dimension.
- Straps 16 ga. and heavier can be fillet welded to structural steel members. The designer shall specify the weld size and length. Welding and specification shall be in compliance with the current American Welding Society ANSI/AWS D1.3, Structural Welding Code – Sheet Steel.
Load Adjustment Factors for Optional Fasteners Used with Straight Straps
- Allowable load adjustment factors shown in the table are applicable to all straight straps throughout this catalog, except as noted in the footnotes below.
- Some products have been tested specifically with alternative fasteners and have allowable load adjustment factors or reduced capacities published on the specific product page. Values published on the product page may be used in lieu of using this table.
- For straps installed over 5/8" maximum wood structural panel sheathing, use a 2 1/2"-long fastener minimum.
- This table does not apply to straps made of steel thicker than 10 ga.
- Where noted, use 0.80 for 10 ga., 11 ga., and 12 ga. products when using SPF lumber.
- Where noted, use 0.92 for 10 ga., 11 ga., and 12 ga. products when using SPF lumber.
When installing floor-to-floor straps, wood shrinkage and compression that occurs during construction may cause the straps to bow out if both ends of the strap are nailed during initial installation.
To prevent this, filling all fastener holes in the strap (including the rim joist area) will limit the bowing. Alternatively, fill the holes in the top of the strap before the roof is installed and then filling the bottom half of the strap after will also help reduce bowing.
Considerations for Hurricane Tie Selection
- What is the uplift load?
- What is the parallel-to-plate load?
- What is the perpendicular-to-plate load?
- What is the species of wood used for the rafter and the top plates? (Select the load table based on the lowest performing species of wood.)
- Will the hurricane tie be nailed into both top plates or the upper top plate only?
- What load or loads will the hurricane tie be taking?
When a connector is loaded simultaneously in more than one direction, the allowable load must be evaluated as option 1 or 2.
Option 1: Unity Equation
For all connectors use the following equation:
Design Uplift / Allowable Uplift + Design Lateral Parallel to Plate / Allowable Lateral Parallel to Plate + Design Lateral Perpendicular to Plate / Allowable Lateral Perpendicular to Plate < 1.0.
The three terms in the unity equation are due to the possible directions that exist to generate force on a connector. The number of terms that must be considered for simultaneous loading is at the sole discretion of the designer and is dependent on their method of calculating wind forces and the utilization of the connector within the structural system.
Option 2: 75% Rule
As an alternative, certain roof-to-wall connectors (reference embedded truss anchors, pp. 254–255, seismic and hurricane ties, pp. 276–279, and twist straps, p. 283 of the Wood Construction Connectors Catalog) can be evaluated using the following: The design load in each direction shall not exceed the published allowable load in that direction multiplied by 0.75.
- Select hurricane tie based on performance, application, installed cost and ease of installation.