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#426 2026-02-08 15:34:28
- SpaceNut
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- From: New Hampshire
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Re: kbd512 Postings
inputted image and question large double torus stiffness problem over long spans need analyzing
You’re poking right at the hard part of these forms—global stiffness over long, curved spans is where they get sneaky.
Key stiffness issues in a large double-torus truss
Global ring flexibility (hoop modes):
The toroidal geometry wants to “ovalize” under asymmetric loads.Problem: Low in-plane bending stiffness of the ring → large lateral deflections, especially midspan between supports.
Watch for: First few modes being global ovalization or “breathing” of the torus rather than local member bending.
Torsional softness of the ring:
If the torus is essentially a single-layer truss ring, its torsional stiffness is often weak.Problem: Eccentric loads (lighting, rigging, façade panels) twist the ring, causing out-of-plane rotations and secondary bending in chords.
Mitigation: Use a closed box-like section at the macro level—e.g., double chord top/bottom with diagonals forming a tube, or two concentric rings tied with radial webs.
Span-to-depth ratio of the truss:
Long spans with shallow truss depth are inherently flexible.Rule of thumb: For a primary long-span truss, depth ≈ span/15–20 is comfortable; much shallower and deflections dominate.
In a torus: “Depth” is the radial distance between inner and outer chords (or top/bottom chords if vertical). Too small → poor bending stiffness around the ring.
Local member buckling vs. global stability:
Compression chords: Long, lightly braced chords around the torus are prone to elastic buckling if panel lengths are large.
Bracing density: Panel length and diagonal layout control effective buckling length; large toroidal spans often need tighter panelization than straight trusses.
Support conditions and continuity:
Discontinuous rings: If the double torus is segmented (e.g., four quadrants bolted together), joint flexibility can dominate global stiffness.
Support layout: Few supports → large bending in the ring between them; many supports → more statically indeterminate, but stiffer and more redundant.
How to analyze stiffness (conceptual workflow)
Idealize as a ring/torus beam first (macro model):Model: Treat each torus as a curved beam with equivalent ?? (bending) and ?? (torsion) derived from the truss.
Goal: Quickly see global deflections, ovalization, and sensitivity to support layout and span.
Derive equivalent section properties from the truss:
Axial stiffness of chords:??eq=∑???cos2(??)
Bending stiffness: Use chord separation (depth) and chord areas to get an equivalent ? about the ring’s local axes.Torsional stiffness: If you have a closed truss tube, approximate ? from the chord layout; if it’s open, accept that ?? is small and design bracing accordingly.
Refine with a 3D truss FE model:
Nodes: At each panel point along the torus; include both toroids if it’s a “double” system.
Members: Chords, diagonals, verticals, and any cross-ties between the two tori.
Check:
Nodal displacements under worst-case load patterns.
Member forces and utilization.
Buckling factors (linear eigen-buckling) for global modes.
Pay attention to load patterns that “break symmetry”:
Partial loading: Half-ring or quarter-ring loads often govern deflection and member forces.
Eccentric loads: Loads offset from the ring centroid to excite torsion and out-of-plane bending.
Strategies to increase stiffness over long spans
Increase structural depth:Radial depth: Separate inner and outer chords more; larger radius difference → higher in-plane bending stiffness.
Vertical depth: If the torus is vertical, increase distance between top and bottom chords.
Create a true closed tube:
Double torus as a box: Tie the two tori together with regular radial frames so they act as a single closed section.
Benefit: Huge gain in torsional stiffness and resistance to ovalization.
Densify bracing:
Shorter panels: More nodes, shorter members → higher buckling capacity and better distribution of forces.
Diagonal patterns: Use X-bracing or K-bracing patterns that stabilize both chords effectively.
Stiffen joints and segment connections:
Bolted flanges / sleeves: Ensure segment joints are not the weak link; rotational slop here kills global stiffness.
Pre-tensioned connections: Where possible, use preloaded bolts or clamps to reduce slip.
Optimize support scheme:
More supports: If feasible, add intermediate supports to reduce effective span between supports.
Support stiffness: Model support flexibility (e.g., base plates, anchors) realistically—soft supports can negate gains in the truss.
A quick gut-check for your design
If you tell me:Major radius (centerline of torus), Minor radius / truss depth, Number of panels, Chord sizes, and Support locations,
I can walk through a rough equivalent ??, estimate deflections over the longest span, and flag where the double-torus concept is likely to feel “soft” versus robust.
What’s the approximate diameter and depth of the double torus you’re thinking about, and is it for a stage, a roof, or something more permanent?
it indicates that the secondary members made from 30×2 mm is fine. but the primary need to be Much larger chord tubes (think on the order of 150–400 mm OD, with sensible wall thickness), and Real truss depth between chords and between the two tori to build up ?eff.
That is an ouch to support the regolith mass...
150–400 mm OD 4–12mm wall thickness
Truss depth (within each torus) 1–3m between inner/outer or top/bottom chords
Separation between the two tori 20–30m center‑to‑center (this is the single biggest lever on global stiffness)
Panel length 5–10m spacing between nodes
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#427 Yesterday 17:18:31
- SpaceNut
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- From: New Hampshire
- Registered: 2004-07-22
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Re: kbd512 Postings
I believe that I have found a means to our goal in using regolith and thermoplastics powder was used as the binder for solid shaping the Vectren regolith bags.
See the torus topic for using regolith plus thermoplastics powder and the wiki reference that I have put together. Wiki New building materials and method
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#428 Yesterday 23:29:53
- kbd512
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- Registered: 2015-01-02
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Re: kbd512 Postings
SpaceNut,
If available engineering data indicates that regolith-filled Vectran is a lower mass solution which remains long-term viable, then we're rolling with that idea. Your solution seems like it should work well enough. I'm happy with using polymer to bind the regolith together. Most "first ideas" tend to be sub-optimal. The exoskeleton framing was only an idea intended to recycle some of those Starships, since many of them are never leaving after they land. If we don't send Starships all the way to the surface, then they're not "lost" to our inability to deliver enough power and equipment to refuel them. I'm not an architectural engineer, so it was no surprise and of little consequence that the first idea I had turned out not to be the best way to build something large enough to house 1,000 people on Mars. That's why we iterate design concepts until something approaching optimal is arrived at. Payload mass not devoted to heavy but relatively weak steel can now be allocated to other necessary equipment.
Do you think we're going to need to "pre-heat" the regolith for adequate mixing of the polymer binder?
Vectran's maximum continuous service temp is 200C, but ideally it should remain between 149C and -62C to avoid loss of fiber tenacity. Vectran melts at 330C. While Vectran fabric is used over temperatures outside this range in LEO, for this to be a very long-term structure we want to avoid creep, which happens faster to polymer fibers when they're placed under load near the edges of their service temperature envelope. The interior fabric layers will be impregnated with Silicone to seal the interior to prevent loss of atmospheric gases. We may want multiple to use multiple Silicone impregnated layers as insurance against punctures. Vectran fiber is already commonly coated with small amounts of Silicone to reduce fiber-to-fiber abrasion, but the kind of Silicone I'm talking about using is a "rubberized" solid. So far as I'm aware, there is no out-gassing issue with these materials aboard ISS, meaning they're approved aerospace materials for human space flight applications. Bigelow Aerospace's BEAM module uses these materials and is presently attached to ISS, but many layers of fabric are used because they're part of an inflatable structure. There is (obviously) no Martian regolith inside them to provide radiation protection, as ISS is largely shielded from CME / SPE / GCR by Earth's Van Allen Belts.
I'm going to introduce the idea of using two additional materials for enhanced fire and impact protection:
I feel as though some sort of thermally and electrically insulating liner material should be applied to the interior wall of the habitat to inhibit accidental fire damage as well.
1. CarbonX fibers "interlock" when exposed to extreme heating, "sealing" the fabric against further heat transfer. I think the interior should be lined with this fabric. Colors are very limited, dark grey or dark blue or black. That might not be ideal for "ambiance", but it is a near-ideal "fire blanket" to protect the interior from fires.
2. To enhance structural integrity to preclude a collapse under the weight of the regolith, we could embed uni-directional fiberglass "bow staves" laced into the interior structure. At ~1,800kg/m^3 of Martian regolith, presuming 2m of overhead protection, the "load" is roughly 280lbs/ft^2. Even with a polymer binder for the regolith and use of a very strong fabric like Vectran, a little additional insurance against a structural failure won't add that much weight.
Here's a photo of a unidirectional fiberglass composite main landing gear bow used for light aircraft:
Placing these supports bows inside the habitat, and possibly outside as well, would ensure that the structure remains adequately supported following some kind of impact event. Maybe they're not needed, but I don't know how regolith with polymer binder behaves under impact at low temperatures.
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#429 Today 02:16:12
- SpaceNut
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- From: New Hampshire
- Registered: 2004-07-22
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Re: kbd512 Postings
The regolith is heat treated to remove water, co2 ice and any other but that's what we want to do anyways to get these in abundance, Whether we have other sources or not for these. The Regolith is ground to make it a bit finer before adding the plastic powder but I do not think that's outside of the scope for equipment that makes building on mars easier.
Something to note is typical binders ( sulfur) need more heat and from what I have seen does not make for something which does the complete function. Using the even thin plate shaped steel around the Plastic provides more protection.
I did see the temperature range of the Vectren fiber plus the work on the ISS multiple layers to sustain pressure. Mixing parts of each Idea looks promising as the Polymer/regolith use can take on the shapes that we desire.
The only issue I have found is the internal needs to have a support system that does not puncture or cause wear to the inflatables material while its loaded up with floors and equipment as that load is how gravity mass of the items go through.
Looks like a metalized foil for the fire safety.
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