Quake Defender sizing calculator
Size the Quake Defender.
Straight from your elastic model.
Apply a 0.1g equivalent static case to an elastic, DonoBrace-only model of the building, enter the results, and the calculator picks the smallest QD and DonoBrace pair that passes the Step 3 locking checks and the Step 4 one-point checks. This page is for sizing only: re-run your model with the chosen size and complete the full design in your own calculations.
QD155 + DB20 passes
Smallest size that passes the Step 3 locking checks and the Step 4 one-point checks.
QD travel at ULS
20.3of 33 mm
QD travel at CALS
46.2of 50 mm
Ductility μ at ULS
2.15
Brace force at ULS
137.6kN
DonoBrace alone, Cat 4 / Cat 3
DB25 / DB25
| Size | QD105 + DB15est.estimated | QD155 + DB20modelyour model | QD280 + DB25est.estimated |
|---|---|---|---|
| T,e (s) | 0.763 | 0.661 | 0.579 |
| Locking | 0.76 | 0.60 | 0.36 |
| ULS | 1.10 | 0.86 | 0.59 |
| CALS | 1.23 | 0.96 | 0.65 |
| μ at ULS | 3.00 | 2.15 | 1.37 |
| δ at ULS (mm) | 34.1 | 20.3 | 7.8 |
| δ at CALS (mm) | past stop | 46.2 | 21.6 |
| Result | Fail | Pass | Pass |
Locking, ULS and CALS are demand ÷ limit, passing at 1.00 or less. μ is the actual displacement ductility at the ULS performance point, Δ,PP ÷ Δ,y; Category 2 (S,p = 0.7) needs μ above 1.25. Sizes other than your model’s are estimated by scaling the brace stiffness; re-run your model with the size you choose.
- CALS check ratio is 0.96, within 5% of the limit. Confirm with your model (Step 7).
Your model
What the calculator reads from it
| Load case V/W, from T,e and the roof displacement | 0.100 g |
| ÷ the 0.1 g applied, 1.00 when the period, seismic weight and displacement are consistent | 1.00 |
| Share of roof displacement from brace axial elongation, (axial elongation ÷ cos θ) ÷ roof displacement | 100% |
| Storey shear taken by the braces | 100% |
Device
QD155 hysteresis, full loop to the hard stop
The dots show where the SLS, ULS and CALS points sit on the loop, the same points as on the ADRS below. The green dot is the Step 3 SLS locking-check force, 52.4 kN: the larger of the SLS brace forces at T,e and at the full-bar-area period, which should stay below the LBH slip force. The SLS point on the ADRS below is the displacement demand at T,e. ULS travel is limited to 33 mm; at CALS the QD may travel to its hard stop at 50 mm.
| kN | LBH | Nominal | UBH |
|---|---|---|---|
| F,slip at 1 mm | 87.3 | 97.0 | 106.7 |
| F,ult at 50 mm | 190.3 | 200.0 | 209.7 |
| F,restoring | 131.7 | 122.0 | 112.3 |
| F,residual | 28.7 | 19.0 | 9.3 |
| F at 33 mm | 154.6 | 164.3 | 174.0 |
F,max for capacity design is the UBH force at 50 mm: 209.7 kN (163.7 kN along the direction of loading).
Step 3
Locking checks for QD155 + DB20
The QD must stay locked for SLS earthquake and ULS wind: the SLS brace force is compared with the lower-bound (LBH) slip force, and 1.3 × the wind brace force with the nominal slip force.
| Locking | Brace force kN | F,slip kN | Ratio | |
|---|---|---|---|---|
| SLS earthquake, Fb,SLS | 52.4 | 87.3 LBH | 0.60 | Pass |
| 1.3 × ULS wind, 1.3 Fb,wind | 52.0 | 97.0 nominal | 0.54 | Pass |
Step 4
One-point checks for QD155 + DB20
Governing ULS limit: Roof: Δ,stop / 1.5, Δ,lim = 86.2 mm. Activation at Δ,y = 32.9 mm; hard stop at Δ,stop = 129.3 mm.
| Check | λ | Δ mm | T s | ξ | S,d mm | Limit | |
|---|---|---|---|---|---|---|---|
| ULS, at Δ,lim | 1.00 | 86.2 | 0.866 | 11.4% | 74.2 | ≤ 86.2 | Pass |
| ULS, device at 33 mm | 1.00 | 95.9 | 0.884 | 11.3% | 76.2 | ≤ 95.9 | Pass |
| CALS, at δ,stop | 1.50 | 129.3 | 0.931 | 10.9% | 123.8 | ≤ 129.3 | Pass |
| Ductility μ > 1.25, at 1.25 Δ,y | 1.00 | 41.2 | 0.722 | 8.0% | 68.3 | ≥ 41.2 | Pass |
The ductility check confirms μ above 1.25 from one spectrum reading. The actual ductility at the ULS performance point is μ = 2.15.
Preliminary Step 7
SLS, ULS and CALS performance points for QD155 + DB20
A preliminary version of methodology Step 7, from the estimated backbone; confirm it with the cyclic pushover of your model (Steps 5 to 7). The estimated capacity curve against the damped demand spectra, with the spectrum reduced by S,p,DDBD = (1 + S,p)/2 = 0.85 (Marriott 2018). Each performance point is where the capacity curve meets the spectrum for its own effective damping. The SLS point is on the T,e line of your DonoBrace-only model; the capacity curve includes the small flexibility of the locked QD, so the SLS point sits slightly above it.
| Performance point | Δ mm | δ mm | Brace kN | V/W | T,eff s | ξ,eff |
|---|---|---|---|---|---|---|
| SLS (QD locked) | 15.0 | 0.5 | 46.1 | 0.138 | 0.661 | 5.0% |
| ULS | 70.9 | 20.3 | 137.6 | 0.413 | 0.831 | 11.2% |
| CALS (λ = 1.50) | 121.8 | 46.2 | 192.0 | 0.577 | 0.922 | 11.0% |
ULS drift × k,dm = 1.42% (limit 2.5%); stability coefficient θ = 0.029, so P-delta analysis is not required (NZS 1170.5 cl 6.5.2(c)); DB20 utilisation 0.59. Recentring (preliminary Step 9): the UBH residual force gives a restoring V/W of 0.0279 against the P-delta demand Δ,y,UBH ÷ h = 0.0060, a ratio of 4.64, so the line recentres.
Comparison
The same line with DonoBrace alone
Two DonoBrace-only designs of the same line to NZS 3404:
- Both: S,p = 0.9, period from the full bar area, displacements from the SRF stiffness.
- Category 4 (elastic, μ = 1.0): the DonoBrace method. C,s = 1.0.
- Category 3 (nominally ductile, μ = 1.25, NZS 3404 Table 12.2.4): design action ÷ k,μ = 1.15 (NZS 1170.5 cl 5.2.1.1), elastic displacement × μ (cl 7.2.1.1), and strength × C,s = 1.1 for a 1 to 2 storey tension-braced frame (NZS 3404 cl 12.12.6.3.2).
- Bar size: the smallest bar with N* ≤ φN,t, drift × k,dm ≤ 2.5% (NZS 1170.5 cl 7.5.1), and brace stress at the CALS displacement ≤ 1034 MPa, the bar’s ultimate strength.
| QD155 + DB20 | DB25 alone, Cat 4 | DB25 alone, Cat 3 | |
|---|---|---|---|
| ULS brace force | 137.6 kN | 269.7 kNof φN,t 366.7 | 258.8 kNof φN,t 366.7 |
| ULS base shear coefficient V/W | 0.413 | 0.810C,s 1.0 × C,d 0.810 | 0.777C,s 1.1 × C,d 0.707 |
| Load path (method basis) | 209.7 kNF,max | 299.7 kNelastic, S,p = 1.0 | 458.4 kN1.25 φN,t, (4)(c) |
| End connections (overstrength) | 339.0 kN | 299.7 kNelastic cap, S,p = 1.0 | 458.4 kN1.25 φN,t, (4)(c) |
| ULS drift with k,dm | 1.42%limit 2.5% | 1.35%limit 2.5% | 1.47%limit 2.5% |
| SLS drift | 0.25% | 0.22% | 0.22% |
| P-delta analysis (NZS 1170.5) | θ 0.029not required, cl 6.5.2(c) | θ 0.014not required, cl 6.5.2(b) | θ 0.017not required, cl 6.5.2(b) |
| CALS | 121.8 mmδ 46.2 of 50 mm | 103.9 mm845 of 1034 MPa | 103.9 mm845 of 1034 MPa |
DonoBrace overstrength actions are 1.3 N,t, capped at the elastic response (NZS 3404 cl 12.9.1.2.2(4)(b); for Category 4 the S,p = 1.0 elastic actions of cl 12.9.1.2.2(2) are the upper limit). Where the cap governs a Category 3 connection, cl 12.9.1.2.2(4)(c) then sets it at 1.25 × the brace design capacity, 1.25 φN,t, which assumes bolted, pinned or fillet-welded connections.
Show working
Estimated backbone for QD155 + DB20. The capacity curve is built from your model: its elastic part scales with brace force, QD travel adds δ ÷ cos θ, and the base shear coefficient follows the brace force.
| Backbone point | δ mm | F kN | Δ mm | V/W |
|---|---|---|---|---|
| Activation, Δ,y | 1.0 | 97.0 | 32.9 | 0.291 |
| 1.25 Δ,y | 5.2 | 105.8 | 41.2 | 0.318 |
| Governing ULS limit, Δ,lim | 28.1 | 153.9 | 86.2 | 0.462 |
| Device limit, δ = 33 mm | 33.0 | 164.3 | 95.9 | 0.493 |
| Hard stop, Δ,stop | 50.0 | 200.0 | 129.3 | 0.601 |
K/W = (2π/T,e)² / g load case S,a = K/W × Δ,e F(δ) from the QD loop brace flexibility f = axial elongation ÷ force, scaled by (SRF·A) for other bars Δ(δ) = F (f/cos θ + other) + δ/cos θ, other = (Δ,e − e/cos θ) ÷ F,e V/W = F ÷ F-per-g of the braced line + (other elements' stiffness) × Δ T = 2π √(Δ / (g V/W)) ξ = 0.05 + A(δ) / (π F cos θ Δ) × braced-line share of V S,d = λ × S,p factor × η(ξ) × C(T) × g (T/2π)² (S,p factor per the S,p option chosen)
Disclaimer
For sizing only: the real configuration is checked in the full structural model. Single-storey structures under 15 m with DonoBrace tension-only bracing, X-braced in pairs so one brace is always effective in tension (NZS 3404 cl 12.12.6.6), to NZS 1170.5:2004. Enter the critical brace for each direction or side: one brace's force and elongation only, regardless of how many braces are on the line. Where a braced line has more than one bay, QD is assumed in every bay of that line. Brace lines resisting the same direction are assumed to activate together: they should use the same QD size and have similar stiffness, or check the torsional response after activation with LBH on one line and UBH on the other. Using QD in both the roof and the walls requires a nonlinear response history analysis. Near-fault sites are outside the methodology. The pushover of your model governs. Uses the Quake Defender Indicative New Zealand Single-Storey Design Methodology V26.10 and its product table. Not a Producer Statement or code opinion; the PS1 signatory remains responsible for the design.