Videos

Tie-Down System Looseness

Ratchet TUDs vs. Screw TUDs

(TUD = Take-Up device)

(5:11) Tiedown systems are designed for system strength and for system elongation. The strength limit is the strength of the weakest item in series between reaction points.

The elongation limit is calculated by the following equation:

System Δ = Σ  shrinkage-TUD compensated shrinkage (If a TUD is used),

+Δ Rod 1 +Δ Rod 2 +Δ Rod 3 etc. + Δ  Plate (or HD(s)+ Δт of TUD (if used).

Note: Δт of TUD = (Δʀ + Δᴀ (Pᴅ /Pᴀ )). Note: Δʀ is added in full.

This video demonstration only shows the shrinkage that occurs in buildings and the Compensation for shrinkage that a ratchet TUD or screw TUD can provide. The Δʀ number that appears in the ICC-ES code report for the TUD is the intrinsic movement that a TUD device will add to the looseness of the assembly.

Note that Δʀ (Delta R) is an average of as few as only 5 tests. A screw TUD will typically have 0.000”-0.003” of residual looseness while a ratchet TUD may have from 0.025 to 0.150” of looseness.

Commentary

Tie-Down system looseness comes from gaps that appear when boards are cut short plus looseness that comes from shrinkage/settling in the building. This looseness typically ranges from 1/4” to 1/2″ per floor. Shrinkage compensators are used to eliminate this looseness by either expanding (screw type TUD) or by ratcheting on the rod (Ratchet type TUD). Each TUD type has inherent looseness. ICC-ES reports the movement as Delta R (Δʀ). I call this movement “Elongation without load”.

This video shows the difference between a ratchet type TUD and a screw type TUD.

The looseness is cumulative and is added to all the other looseness in the system. As the building settles and shrinks and the rod stays constant, the settlement and shrinkage from each succeeding floor is added to the whole.

The looseness shown in this video is only due to shrinkage. The total looseness -System Δ – is the sum of the calculated or tested elongations of all items (rod, plate, holdown, TUD etc.)

Tie-Down System Looseness

Ratchet vs Screw TUDs.

(2:48) This video shows the contrast between ratchet type TUDs (Take-Up Devices) and screw type TUDs

Tie-Down System Looseness

No TUD, Ratchet TUDs
and Screw TUDs

(6:12) This video demonstrates the effects of shrinkage in buildings – with and without TUDs (Take-Up Devices)