Guard Post Load and Base Connection
The load guard-handrail-check names and stops at. IBC 1607.8.1 puts a 200 lb concentrated load AND a 50 plf uniform load on a guard, not concurrently -- so past 4 ft of post spacing the uniform case quietly takes over, and at 6 ft it is 300 lb, not 200. The real finding is where the trouble is: 300 lb at 36 in is 10,800 in-lb, which a 4x4 carries at 1,511 psi of bending, but the base connection has to resolve that same moment across maybe 4 in of bolt spacing -- 2,700 lb per side, NINE times the applied load. The lever arm collapsed from 36 in to 4 and multiplied the force by exactly that ratio, which is why deck guards fail at the rim joist and not at the post, and why lag screws into rim end grain are not acceptable. Allowable bending stress is an input (species, grade, NDS factors). Fastener, rim, and load-path capacity are not checked.
Formula and source
uniform load at a post = 50 plf x post spacing; governing load = max(200 lb concentrated, uniform at post), the two being non-concurrent; base moment = governing load x post height; post S = b d^2 / 6 on ACTUAL dimensions; required Fb = moment / S; connection couple force = moment / fastener lever arm; force multiplier = post height / lever arm.
IBC 1607.8.1 - handrails and guards designed for a 50 pound per linear foot uniform load and a 200 pound concentrated load, with the uniform load not assumed to act concurrently with the concentrated load. Intermediate rails, balusters, panel fillers, and guard infill carry a separate 50 pound concentrated load under 1607.8.1.1 and 1607.8.1.2, which this tile names but does not check. Everything after the load is statics.
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