Seismic and wind events are serious threats to structural integrity and occupant safety. All wood-framed buildings need to be designed to resist shearwall overturning and roof-uplift forces. For one- and two-story structures, connectors (straps, hurricane ties and holdowns) have been the traditional answer. With the growth in mid-rise, wood-framed structures, however, rod systems have become an increasingly popular lateral and uplift restraint solution.
Multi-story structures present complicated design challenges. Frequently, the structures have larger windows and door openings, providing less space for traditional restraint systems. For all these reasons, there is increased need for restraint systems that can meet multi-story structural demands without sacrificing installation efficiency or cost considerations.
Continuous rod tiedown systems are able to answer these demands by restraining both lateral and uplift loads, while maintaining reasonable costs on material and labor. Instead of using metal connector brackets as in a holdown system, continuous rod tiedown systems consist of a combination of rods, coupler nuts, bearing plates and shrinkage-compensation devices. These all work together to create a continuous load path to the foundation.
Contact a Simpson Strong-Tie representative for help designing your Strong-Rod continuous rod tiedown solution.
Continuous rod tiedown systems are used to resist two types of tension forces — shearwall-overturning forces and uplift forces on roofs.
One type of tension force is a result of lateral (horizontal) forces due to a wind or seismic event. This force occurs at the end of shearwalls and its magnitude increases at lower levels as it accumulates the tension force from each level or shearwall above.
Roof uplift tension forces are those net vertical wind forces that occur as uplift loads at the bearing points of roof trusses or rafters of a structure. In moderate-to high-wind areas, these forces are generally resisted by rafter-to- top-plate connections in combination with tiedown systems spaced uniformly along exterior and interior bearing walls.
To ensure structural stability, a continuous rod tiedown system can be used in a mid-rise wood-framed structure to resist shearwall overturning and roof uplift.
Simpson Strong-Tie Strong-Rod Systems provide both an Anchor Tiedown System for shearwall overturning restraint (Strong-Rod ATS) and an Uplift Restraint System for roofs (Strong-Rod URS).
Strong-Rod ATS solutions address the many factors that must be considered during design to ensure proper performance against shearwall overturning — such as rod elongation, wood shrinkage, construction settling, shrinkage compensating device deflection, incremental loads, bearing plate bending, cumulative tension loads and anchorage.
Strong-Rod URS solutions address the many factors that must be considered during design to ensure proper performance to resist roof uplift — such as rod elongation, wood shrinkage, rod-run spacing, wood top-plate design (connection to roof framing, reinforcement at splices, bending and rotation restraint), and anchorage.
Simpson Strong-Tie Strong-Rod Systems have been extensively tested by our engineering staff at our state-of-the-art, accredited labs. Our testing and expertise have been crucial in providing customers with code-listed solutions. The Strong-Rod URS solution is code-listed in evaluation report ICC-ES ESR-1161 in accordance with AC391, while the take-up devices used in both the ATS and URS solutions are code-listed in evaluation report ICC-ES ESR-2320 in accordance with AC316.
A large number of factors need to be considered when specifying a rod system:
Simpson Strong-Tie is here to help you. We provide complimentary design services to help engineers with their continuous rod design. Since no two buildings are alike, each project is optimally designed to the Designer's individual specifications. Run-assembly elevation drawings and load tables are provided to the Designer for approval. For our design support services, contact your Simpson Strong-Tie representative at (800) 999-5099 or visit strongtie.com/srscontact.