Wood Construction Connectors General Instructions for the Designer
These general instructions for the Designer are provided to ensure proper selection and installation of Simpson Strong-Tie Company Inc. products and must be followed carefully. These general instructions are in addition to the specific design and installation instructions and notes provided for each particular product, all of which should be consulted prior to and during the design process.
- The term "Designer" is intended to mean a licensed/certified building design professional, a licensed professional engineer, or a licensed architect.
- All connected members and related elements shall be designed by the Designer.
- All installations should be designed only in accordance with the allowable load values set forth in this catalog.
- Unless otherwise noted, connector allowable loads published in this catalog are limited to the lowest of: average recorded test load at 1⁄8" deflection, lowest ultimate recorded test load of three tests specimens divided by three (or the average of six specimens divided by three), or the calculated value based on steel, wood bearing, and/or fastener capacity.
- When a connector is loaded simultaneously in more than one direction, the allowable load must be evaluated as shown here. 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.
As an alternate, certain roof to wall connectors (Embedded Truss Anchors, Seismic and Hurricane Ties, and Twist Straps) 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. For connections involving members with different specific gravities, use the allowable load corresponding to the lowest specific gravity in the connection, unless noted otherwise.
- Loads are based on the 2015 National Design Specifications (NDS) and AISI S100-12 if applicable, unless otherwise specified. Other code agencies may use different allowable loads.
- Unless otherwise noted, loads include Load Duration, Group Action and Toe-Nail factors from the NDS as applicable. The application of additional adjustment factors shall be by the Designer. Duration of load adjustments as specified by the code are as follows:
“PERMANENT” — 90% of the design load.
“FLOOR” and “DOWN” (100) — no increase for duration of load.
“SNOW” (115) — 115% of design load for 2 month duration of load.
“ROOF LOAD” (125) — 125% of design load for 7 day duration of load.
“EARTHQUAKE/WIND” (160) — 160% of design load for earthquake/wind loading.
- Unless otherwise noted, wood shear is not considered in the loads given; reduce allowable loads when wood shear is limiting.
- Simpson Strong-Tie strongly recommends the following addition to construction drawings and specifications:
“Simpson Strong-Tie® connectors are specifically required to meet the structural calculations of plan. Before substituting another brand, confirm load capacity based on reliable published testing data or calculations. The Engineer/Designer of Record should evaluate and give written approval for substitution prior to installation.”
- Verify that the dimensions of the supporting member are sufficient to receive the specified fasteners, and develop the top flange bearing length.
- Some catalog illustrations show connections that could cause cross-graintension or bending of the wood during loading if not sufficiently reinforced. In this case, mechanical reinforcement should be considered.
- For holdowns, anchor bolt nuts should be finger-tight plus 1⁄3 to 1⁄2 turn with a hand wrench, with consideration given to possible future wood shrinkage. Care should be taken to not over-torque the nut. Impact wrenches should not be used as they may preload the holdown.
- Simpson Strong-Tie will provide upon request code testing data on all products that have been code tested.
- The allowable loads published in this catalog are for use when utilizing the traditional Allowable Stress Design methodology. A method for using Load and Resistance Factor Design (LRFD) for wood has been published in ASTM D5457. A method for using LRFD for cold-formed steel has also been published in the AISI S100-07. When designing with LRFD, reference lateral resistances must be used. Contact Simpson Strong-Tie for reference lateral resistances of products listed in this catalog. For more information, refer to the 2012 NDS Appendix N, which contains a conversion procedure that can be used to derive LRFD capacities.
- For joist hangers, Simpson Strong-Tie recommends the hanger height shall be at least 60% of joist height for stability against rotation while under construction prior to sheathing install.
- For cold-formed steel applications, as a minimum all screws must comply with Society of Automotive Engineers (SAE) Standard J78, Steel Self-Drilling/Tapping Screws, and must have a Type II coating in accordance with ASTM B 633, Electrodeposited Coatings of Zinc on Iron and Steel. Screw strength shall be calculated in accordance with AISI S100-07 Section E4, if applicable, or shall be based on the manufacturer’s design capacity determined from testing.
- Local and/or regional building codes may require meeting special conditions. Building codes often require special inspection of anchors installed in concrete and masonry. For compliance with these requirements, it is necessary to contact the local and/ or regional building authority. Except where mandated by code, Simpson Strong-Tie products do not require special inspection.
- Holdown and Tension Tie allowable loads are based on installations with an anchor rod length of 6" from the concrete to top of holdown seat, yet these products may be raised to any height with consideration of the increased deflection due to additional bolt elongation. For cases where the anchor bolt is offset, Simpson Strong-Tie offers recommendations, subject to the approval of the Designer, which permit holdowns to be raised up to 18" maximum with a corresponding horizontal anchor bolt offset of 1 1⁄2". See “General Instructions for the Installer” (note q).
- Throughout the catalog there are installation drawings showing the load transfer from one element in the structure to another. Additional connections may be required to safely transfer the loads through the structure. It is the Designer’s responsibility to specify and detail all necessary connections to ensure that a continuous load path is provided as required by the building code.
- Top flange hanger allowable loads are typically based on testing with solid headers. Load reductions may apply when using headers comprised of multiple plies of dimensioned lumber or SCL.
See technical bulletin T-C-MPLYHEADR16 for more information.