A turbine-generator table-top foundation's own shipped default inputs fail two checks at once — deck and raft minimum steel — purely because the engine applies the 0.0018 shrinkage ratio to the full member thickness, a real disclosed quirk a good idea to understanding rather than a modelling bug.
Every check above runs automatically inside the Structyze Turbine Foundation module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
The Example We'll Use
- Deck 26 × 16.4 ft × 40 in, on 8 columns, 24 in square, 33 ft tall
- Raft 33 × 23 ft × 60 in
- Turbine weight 562 kip, operating speed 3000 rpm
- Allowable bearing 5.2 ksf
Working Through It
Static bearing, summing deck, columns, raft and turbine weight (≈ 1500 kip) over the raft's plan area, gives q ≈ 1.99 ksf against 5.2 ksf allowable — wide margin, utilisation 0.38.
The vertical resonance check models the 8 columns as parallel axial springs under the rigid deck-plus-turbine mass: fn ≈ 22.7 Hz against an operating frequency fop = 3000/60 = 50 Hz, giving a ratio of 0.45 — safely outside the 0.5–1.5 resonance danger band.
Column slenderness flags as a warning: kℓu/r = 55 against the short-column limit of 22, more than double — expected for 33 ft-tall columns, and specifically the signal that this table-top frame needs wind, seismic and machine-horizontal-dynamic-force design, none of which this module performs.
What Governs, and Why
Deck and raft minimum-steel checks both fail outright (utilisation 1.39 and 1.48) — but this is a real, disclosed quirk of how the engine applies ACI 318's 0.0018 shrinkage-and-temperature ratio to the full member thickness. Cl 24.4.3.2 actually permits capping that steel at the amount needed for a nominal ~18 in thickness on a genuinely thick member; applying that cap (or simply providing tighter bar spacing, like #5 at 4 in in the deck) clears both checks without changing the section at all.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze Turbine Foundation module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
For Turbine Foundation and the rest of the full catalogue — 80+ components across RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
Why would the module's own defaults fail a basic minimum-steel check?
It's a disclosed simplification, not an error in the underlying engineering: applying the 0.0018 ratio to the full 40 in or 60 in thickness overstates what ACI 318 Cl 24.4.3.2 actually requires for a very thick member, since the code itself allows capping shrinkage steel at the amount a nominal ~18 in section would need. The fix is a straightforward bar-spacing adjustment, not a redesign.
Why does vertical resonance matter more here than static bearing?
Static bearing has generous margin (0.38) because a table-top foundation is sized primarily for stiffness against dynamic amplification, not for soil bearing capacity — the real design driver is keeping the foundation's natural frequency well clear of the machine's operating frequency, which is exactly what the resonance check, not the bearing check, is verifying.
Final Thoughts
The deck and raft minimum-steel 'failures' here are a truly useful lesson: a check failing doesn't always mean the design is wrong — sometimes it means the simplified check itself needs a documented code-permitted adjustment before drawing conclusions.