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Tie Down Systems in LAVA

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Overview

LAVA provides integrated design and analysis of continuous tie-down rod systems used with wood shear walls. During analysis, LAVA automatically selects and verifies the complete tie-down assembly, including the rod, take-up device, bearing plate, and coupler, while also evaluating the effect of the anchorage system on overall shear wall drift.

The tie-down system is designed to satisfy both strength and stiffness requirements. Material selection is performed automatically using the selected manufacturer database while considering wall geometry, constructability requirements, and user-defined deformation limits.

LAVA currently supports tie-down systems from:

  • Simpson Strong-Tie

  • Earthbound

  • MiTek

  • AutoTight

Design Process

When a model is analyzed, LAVA designs the tie-down system in the following sequence.

  1. Select the required shear wall sheathing.

  2. Select an appropriate tie-down rod.

  3. Select a compatible take-up device (TUD).

  4. Select a compatible bearing plate.

  5. Select a compatible coupler between rod segments.

  6. Verify system deformation and wall drift.

Each component is selected using the manufacturer's published capacities and compatibility requirements while considering the demands from the structural analysis.

Sheathing Selection

The required shear wall sheathing is selected first.

Selection considers:

  • Seismic Design Category

  • Wall location

  • Selected shear wall material

  • Constructability requirements

  • Required shear capacity

If no acceptable wall assembly is available, the wall is reported as “Wall Failed!” and it will report vmax > vallow →NG

Rod Selection

After the wall sheathing has been selected, LAVA determines the required rod.

Rod selection considers:

  • Required overturning tension

  • Selected rod grouping (fully threaded, high strength, etc.)

  • Wall size (2×4, 2×6 or 2×8)

  • Practical bore size through the framing

  • Coupler compatibility between levels

If an acceptable rod cannot be found, LAVA reports one of the following:

  • Rod Overstressed

  • Rod / Cavity Size Conflict

Take-Up Device Selection

The take-up device (TUD) is selected after the rod has been determined.

Selection considers:

  • Rod diameter

  • Required tensile capacity

  • Available travel

  • User-defined shrinkage allowance

  • User-defined fit-up allowance

Bearing Plate Selection

Bearing plates are selected based on:

  • Rod diameter

  • Take-up device size

  • Wall thickness

  • Bridge distance between posts

  • Bearing capacity

Coupler Selection

Couplers are selected automatically to connect rod segments between floors.

Selection considers:

  • Rod size above

  • Rod size below

  • Rod steel grade

  • Manufacturer compatibility

Stiffness Analysis

After the strength design is complete, LAVA evaluates the contribution of the tie-down system to overall wall deformation.

The following deformation components are included:

  • Shear deformation

  • Flexural deformation

  • Rod elongation

  • Take-up device deformation

  • Take-up device seating

  • Bearing plate crushing

  • Top plate crushing

  • Sill plate crushing

These components are combined to determine the total anchorage deformation, which is then included in the overall shear wall drift calculation.

If the calculated drift exceeds the allowable limit, LAVA automatically attempts to increase system stiffness by selecting stiffer wall assemblies, larger rods, or stiffer take-up devices while maintaining compatibility with the selected manufacturer database.

If no acceptable solution is found, Drift Limit Exceeded is reported.

Rod Run Summary

LAVA provides a rod run summary showing the selected components for every level of the structure.  This can be found in the Calculation Log, Summary tab.  This tab is available when it is enabled in the Log tab prior to running the analysis.  

The report includes:

  • Shear Wall Name

  • Size (SW Mark)

  • Z0 Rod (Start end)

  • Z0 Lvl Cumulative Tension by level (lbs)

  • Z0 Lvl Cumulative Compression by level (lbs)

  • Z1 Rod (Finish end)

  • Z1 Lvl Cumulative Tension by level (lbs)

  • Z1 Lvl Cumulative Compression by level (lbs)

This summary allows the engineer to verify the complete load path from the roof to the foundation.  This allow allows the engineer to share this information with the tie-down manufacturer.