Crab & Monolith
Crab
I've been puzzling over how to support a large span with the least material—triangular trusses keep the forces in a straight line, but I wonder if there's a more optimal shape. What do you think?
Monolith
Triangles keep forces straight; if you can let the shape carry bending, a curved arch or tensegrity can save material, but every member still needs to be in pure compression or tension. Try a geodesic shape—it spreads load more evenly and often needs less material.
Crab
Geodesic is a solid idea—loads spread evenly, each member stays in compression. But then you have to keep a lot of joints, which adds weight and complexity. Maybe a hybrid: a semi‑elliptical arch with a few key struts that lock it in place. That could keep the bending in the arch and the joints minimal. Have you plotted the stress distribution yet?
Monolith
I haven’t run a full analysis yet, but a semi‑elliptical arch with a few diagonal struts will put most members in compression. The key is to keep the arch’s curvature tight enough that the joint forces stay small; otherwise the added joints offset the savings. I’ll sketch the load paths and let you see where the stresses peak.
Crab
That sounds logical—tight curvature keeps the joints in compression and reduces bending moments. While you sketch the load paths, double‑check the span‑to‑rise ratio; if the rise is too shallow the arch will flex more than you expect. Once you have the stress peaks, we can tweak the strut angles to keep every member well below the material’s yield. Keep me posted on the numbers.
Monolith
Got it. I'll compute the span‑to‑rise ratio, map the stresses, then adjust the strut angles. Will keep you updated.
Crab
Sounds good—once you have the numbers, we can iterate quickly and lock in the most efficient geometry. Let me know what you find.
Monolith
Will run the calculations now. I'll send you the results once they're ready.
Crab
Go ahead and crunch those numbers. I’ll be ready when you’re done.
Monolith
Span‑to‑rise set at 4:1 gives an arch rise of 2.5 m over a 10 m span.
Maximum compressive stress on the arch’s lower curve ≈ 180 MPa; top curve drops to about 90 MPa.
Diagonal struts hit peak stresses of ~120 MPa at their joints, all below the material yield of 250 MPa.
If we shift the strut angles from 30° to 25°, the joint loads drop by roughly 10 %. Keep those values in mind for the next iteration.
Crab
Great data—those stress values look comfortable, but that 10 % drop in joint loads with 25° angles is significant. I’d suggest also looking at the axial force in the arch at the apex; if it stays low, you can push the rise a bit higher and reduce the total material. Keep checking the buckling capacity for the struts too. Let's aim to keep everything under 80 % of the yield, just in case of unexpected load spikes. Once you have the updated numbers, we can refine the geometry further.