Simpson Strong-Tie® Strong-Rod™ Uplift Restraint System for roofs (Strong-Rod URS) provides tiedown solutions comprising steel components, which include threaded rods, bearing plates, nuts, coupler nuts and take-up devices. Top plate(s), blocking, and other wood members that transfer uplift load to the tiedown runs are not provided by Simpson Strong-Tie.
Simpson Strong-Tie provides uplift restraint systems for roofs to meet the design uplift forces. These forces are provided and determined by the Designer and governing jurisdiction requirements. During preliminary design, Simpson Strong-Tie may determine estimated loading; however, the Designer is responsible for final design, calculations or derivation of structural forces related to the building. Simpson Strong-Tie has not confirmed and is not responsible for verifying the uplift restraint system adherence to the governing jurisdiction’s deflection requirements or its performance in consideration of structural deformation compatibility.
Continuous rod systems for uplift restraint include, but are not limited to, top-plate rotation restraint connections, bearing, rod tension, concrete anchorage and wood framing members.
The rod system that provides uplift restraint for roofs should be continuous from the roof-level top plate(s) to the foundation or to the underside of the level where the Designer has determined the tiedown run can terminate due to dead load resistance.
Spacing tables for uplift restraint runs shall be found at the URS Run Tables. The Designer may establish specific detailing and provide calculations approved by the local jurisdiction to allow for increased spacing.
Wood framing members used in top plate and wall stud applications must be either sawn dimensional lumber complying with IBC Section 2303.1.1 or IRC Section R602.1, or structural composite lumber (SCL) recognized in a current ICC-ES or IAPMO UES evaluation report, with nominal dimensions of either 2x4 or 2x6 sizes with a Specific Gravity (SG) in a range of 0.42 to 0.55. Sawn dimension lumber must have a moisture content of 19 percent or less (16 percent for SCL members), both at the time of installation and in service.
Where connection hardware between the roof framing members and the wall top plate induces eccentric loading about the centerline of the top plate, Simpson Strong-Tie top plate-to-stud connections must be installed to prevent top plate rotation. The top plate-to-stud connector used to resist this rotational force must be on the same side of the wall as the roof-to-wall connectors.
The top-plate splice details apply to the “reinforced” top-plate tables available at the URS Run Tables. The splice reinforcement must be attached using 1/4"x 4 1/2" Simpson Strong-Tie® Strong-Drive® SDS Heavy-Duty Connector screws. Otherwise the “unreinforced” top-plate tables must be used.
Fully threaded steel rods used with the roof uplift restraint tiedown runs have diameters of 3/8" through 3/4". The threaded rods are made of ASTM F1554 Grade 36 Class 2A or A307 Grade A, steel.
Threaded rod couplers used to attach threaded rods end to end require proof of positive connection between threaded rods and rod couplers, such as the use of Witness Holes™.
Tabulated values given for the roof uplift restraint runs available at the URS Run Tables take into account the following serviceability limits:
0.18" inch of total rod elongation along the length of the roof uplift restraint run.
A bending deflection limit of L/240 for the top plate(s), where L is the span of the top plate between adjacent tiedown runs.
0.25" of roof uplift restraint total system deflection between the top plate(s) and the termination of the run that includes the total elongation of the rod run and the bending of the top plate(s) between rod runs. The contribution of wood shrinkage to the overall deflection of the continuous rod tiedown system must be analyzed by the Designer. Simpson Strong-Tie recommends the use of a shrinkage compensation device (take-up device) at each run to mitigate wood shrinkage. The tables included in this design guide include the effect of RTUD or ATUD shrinkage compensation devices.
Wood bearing compression under steel bearing plates (up to 0.04").