Open-Cavity Trunk Strength Loss (Smiley & Fraedrich)
The open-cavity correction trunk-decay-strength's note warns about: an open face (wound, seam, fire scar) makes the ring a broken tube, far weaker than the closed-hollow Wagener estimate. loss = (hollow_d^3 + R x (D^3 - hollow_d^3)) / D^3 x 100, where R is the opening arc / circumference (Smiley & Fraedrich 1992). Collapses to Wagener at R = 0; validated against the paper's example (4-in stem 70% hollow, 2-in opening -> 45%). A 24-in trunk with a 3-in wall and an 8-in opening loses 48% vs the 42% a closed hollow shows. A screen, not a load rating.
Formula and source
hollow_d = D - 2t; R = min(1, opening_width / (pi x D)); closed_loss = (hollow_d^3 / D^3) x 100; open_loss = (hollow_d^3 + R x (D^3 - hollow_d^3)) / D^3 x 100.
Smiley & Fraedrich (1992) open-cavity strength-loss formula, by name.
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