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Specification Considerations

Strong-Rod Systems

When specifying Simpson Strong-Tie Strong-Rod Anchor Tiedown System for shearwall overturning restraint, one should consider several factors to ensure that the system is configured to meet the design intent and building codes. These factors apply to each method of specification. The list on the left below delineates the general design requirements for any continuous rod tiedown system used to restrain overturning forces in stacked shearwalls. The list on the right provides a description of how our system is designed and of the services we provide in order to meet the general strength and performance requirements.

General Shearwall Overturning Restraint Rod System

Designer Responsibilities

  • Calculating lateral forces in each floor and roof diaphragm (at diaphragm level) of structure
  • Locating shearwalls in each level of the structure
  • Calculating cumulative overturning tension and compression forces for each shearwall
  • Design and specification of compression posts
  • Design and specification of anchorage to foundation including anchor bolt diameter and grade of steel
  • Drift Check (Seismic)

Information Required to Design Rod Tiedown System

  • Building code edition
  • Building jurisdiction deformation requirements, (if applicable) such as rod elongation and system deformation limits
  • Cumulative overturning tension/compression forces
  • Estimate of wood shrinkage per level
  • Wood framing including size and species of stud, post, sill and sole plates as well as floor system type and depth
  • Fire-Retardant Wood Treatment (FRT) design value adjustment factors when applicable
  • Wall height (finish floor to ceiling)
  • Anchor bolt size and grade at foundation
  • Anchor bolt coating
  • Run start above foundation such as steel or wood beam
  • Run termination preference at top of run (top plate, bridge block, strap)
  • Floor plan shearwall layout

Required Rod System Design Checks

  • Tensile capacity of rod
  • Bearing plate capacity
  • Travel capacity of shrinkage take-up device
  • Load capacity of shrinkage take-up device
  • Rod elongation per level using net tensile area of rod
  • Total system deformation per level
  • Verification that rod elongation plus take-up device displacement is less than or equal to 0.2 inch or less based on jurisdictional or designer requirements. (Per ICC-ES AC316)

Anchorage Design

  • Anchorage design information conforms to ACI 318-14. Designer may also consider Simpson Strong-Tie Shallow Podium Slab Anchorage.

Simpson Strong-Tie Strong-Rod Design Checklist

Rod Tension (Overturning) Check

  • Rods at each level designed to meet the cumulative overturning tension force per level as delivered from bearing plates and transfer it to the foundation
  • Standard and high-strength steel rods designed not to exceed tensile capacity as defined in AISC 360-16 specification
    1. Standard threaded rod based on 36 / 58 ksi (Fy/Fu)
    2. High-strength fully threaded rod for diameters up to 1" based on 92 /120 ksi (Fy/Fu)
    3. High-strength fully threaded rod for diameters 1 1/8" and greater based on 105 /125 ksi (Fy/Fu)
    4. High-strength Strong-Rod for all diameters is based on 92 /120 ksi ((Fy/Fu)
    5. H150 Strong-Rod based on 130 / 150 ksi (Fy/Fu)
  • Rod elongation limits (see below)

Bearing Plate Check

  • Bearing plates designed to transfer incremental overturning force per level into the rod
  • Bearing stress on wood member limited in accordance with the 2018 NDS to provide proper bearing capacity and limit wood crushing
  • Bearing plate thickness is considered for bending when calculating and sizing the plate, and in some cases will govern over simplified full plate bearing on the wood member

Shrinkage Take-Up Device Check

  • Shrinkage take-up device is selected to accommodate estimated wood shrinkage to eliminate gaps in the system load path.
  • Load capacity of the take-up device compared with incremental overturning force to ensure that load is transferred into rod

Movement/Deflection Check

  • System deformation is an integral design component impacting the selection of rods, bearing plates and shrinkage take-up devices
  • Rod elongation plus take-up device displacement is less than or equal to 0.2 inch per level or as further limited by the requirements of the engineer or the governing authority having jurisdiction
  • Total system deformation reported for use in Δa term (total vertical elongation of wall anchorage system) when calculating shearwall deflection
  • Both seating increment (ΔR) and deflection at allowable load (ΔA) are included in the overall system movement. These are listed in the evaluation report ICC-ES ESR-2320 for take-up devices, and are summarized in our job summary

Optional Compression Post Design

  • Compression post design can be performed upon request along with the Strong-Rod System
  • Compression post design limited to buckling or bearing perpendicular to grain on wood plate