Bolt Capacity Calculator

Always compute both and take the lower. Shear checks the bolt itself, 0.6 fub A / 1.25; double shear multiplies the bolt resistance by two but does not multiply bearing — a bolt through three plates works on two shear planes, yet each plate still bears separately, so bearing is taken on the thinner plate. A double-shear joint therefore often flips from shear-controlled to bearing-controlled, and checking a single plane or shear alone overstates the connection. bearing checks the plate, 2.5 ab fu d t / 1.25. The bearing factor ab is the smallest of three ratios — edge e/(3d0), pitch p/(3d0) minus 0.25, and strength fub/fu — capped at 1.0. The usual mistake is checking shear only, and using the gross area: an M20 grade 8.8 looks generous at 120 kN on the gross section, but the threaded stress area gives 94 kN, 28% less. Against a 10 mm S355 plate at 40 mm edge the bearing value is 104 kN, so shear governs here; bearing only takes over below about 9 mm plate. Thin plates and short edge distances lose on bearing, so the fix is more bolts, not bigger ones. Several things here do not show up as a reduced capacity but will tear the connection apart: edge distance below 1.5d0 causes tear-out; pitch below 2.5d0 allows block shear along a row; in a long joint (end bolts more than 15d apart) the shear resistance must be multiplied by beta_Lf = 1 - (Lj - 15d)/(200d), floored at 0.75, because the load does not distribute evenly and the end bolts carry more; and an eccentrically loaded group must be split by polar moment of inertia rather than equally. This tool takes the smallest of the three ab ratios, which applies the worst bolt to all of them and is conservative: strictly the end row uses e1/3d0 and inner rows use p1/3d0 - 0.25, and k1 = 2.5 assumes the transverse edge distance is at least 1.5d0, below which k1 = 2.8e2/d0 - 1.7 governs. These are design values with the 1.25 material factor already applied, so do not compare them with tested failure loads.