Fire Tower (Tier 1 test build) — slenderness vs. load capacity

The problem: the first small, illustrative test tower for the Fire Tower Network, before scaling to the full four-tier spec. 16 ft to platform, 4 corner legs, small 4×4 ft platform for one person + gear.

Load check: total weight ≈ platform framing (150 lb) + occupant/gear (300 lb) = 450 lb ÷ 4 legs ≈ 112 lb per leg — trivial axial load on its own.

New concept this chapter — slenderness ratio as its own, separate check: load capacity and slenderness are two different questions. A member can pass one and fail the other.

4×4 leg (3.5" actual) at 16 ft unbraced

• Le/d = (16×12) ÷ 3.5 ≈ 54.9
• Euler buckling capacity: Pcr ≈ 4,686 lb — ~40× the actual 112 lb load, passes easily by raw strength
• Fails anyway: NDS caps sawn-lumber columns at Le/d ≤ 50 regardless of load. Above that, a post is considered too whippy/unstable to trust, independent of what the stress math says.

Fix (either works)

• 6×6 leg (5.5" actual): Le/d = 192 ÷ 5.5 ≈ 34.9 — clears the limit with room to spare
• Or keep 4×4 legs and add cross-bracing partway up, shortening the unbraced length each leg actually sees

Answer

For a small test tower, 6×6 legs are the simpler build — no bracing geometry to get right. Carry that spec into Tier 2+ as the towers scale up.

Field evidence behind the rule: if a leg flexes noticeably under your own body weight/muscle, wind will move it too — wind hits more area, more often, for far longer than one person leaning on it. The Le/d = 50 limit is the code's version of the same test; a hands-on "can I make it whip" check catches the same problem without a calculator.

Open items for a later pass

Wind load at height (matters far more up here than at ground level — both the force and its overturning moment arm grow with height) and occupant live load code values for an observation platform, once a taller tier is actually being built. Breyer Chapter 5 checks both fixes with the NDS column method and the timber values: the 6×6 leg carries about 7,590 lb at 16 ft (against 112 lb), and 4×4 legs braced at mid-height carry about 6,170 lb.