Moment Connection Design Calculator

Bolts Required comes from dividing Flange Force by Single Bolt Shear Capacity, and those two quantities respond to different inputs. Flange Force is Beam Moment converted to a force couple using the bolt-group lever arm (bolt rows spaced 3" apart), so it rises with Beam Moment and falls as Number of Bolt Rows grows (more rows spread further apart mean less force per bolt). Single Bolt Shear Capacity, on the other hand, depends only on Bolt Diameter and Bolt Grade -- Bolt Diameter has the larger effect of the two on that capacity, because shear strength scales with bolt area (diameter squared), while stepping from A325 to A490 bolts (Bolt Grade) raises the allowable shear stress by a fixed 24% regardless of size. The 68 ksi and 84 ksi nominal shear values behind that jump, and the 0.75 resistance factor applied to them, are the published bolt design values in Table 5.1 of the RCSC's Specification for Structural Joints Using High-Strength Bolts, not figures invented for this calculator.

Because Number of Bolt Rows also directly sets Bolts Provided (2 per row), it is the single input with the largest real swing on both sides of the Demand/Capacity check across its full 2-12 row range -- from 27 bolts required down to 3 as rows increase from the low end to the high end -- even though that swing does not show up in a small nudge around the calculator's default of 4 rows, since bolt count only changes in whole-row, whole-bolt increments. Note that this calculator's own default inputs (200 kip-ft moment, 7/8" A325 bolts, 4 rows) land on a FAILING connection: they require 9 bolts against only 8 Bolts Provided, a Demand/Capacity Ratio of about 1.09, and a red Connection Adequate = Fail result -- so if you load this page and change nothing, the very first result you see is intentionally a fail, meant to demonstrate what an under-designed connection looks like before you add a bolt row or step up bolt size/grade to bring the ratio back under 1.0. This is a preliminary check using a simplified end-plate-thickness estimate (assuming a fixed 8" plate width and 50 ksi steel); it does not replace a full AISC Design Guide 4 or 16 calculation covering prying action, plate yield-line patterns, or weld design.