How to use the eccentric bolt group shear calculator
When a load lands away from the centroid of a bolt group, as it does on a bracket or a gusset plate, each bolt carries direct shear from the load plus torsional shear from the moment that tries to rotate the group. This calculator takes the eccentric shear load, the eccentricity, the bolt layout and the spacing, and returns the polar moment of inertia and the maximum bolt resultant using the elastic vector method.
The math is short. Direct shear is the load divided by the number of bolts. Torsional shear is the moment times the distance from the centroid, divided by the polar moment of inertia. Adding the two as vectors makes the corner bolt farthest from the centroid the critical one, which is the value reported.
Spreading the pattern beats adding bolts. Because the polar moment of inertia is a sum of squared distances, widening the spacing reduces the peak bolt force faster than adding another bolt near the centroid. Edge distance, plate width and erection clearance set the practical limits.
The instantaneous center method would credit more capacity but requires the AISC Manual coefficient tables, so only the conservative elastic method is used here. Bearing and tearout, net section rupture, block shear and the bracket plate itself are separate limit states, so have a licensed structural engineer confirm the connection before it is built.
Frequently asked questions
The elastic vector method adds direct shear and torsional shear as vectors, can be done by hand, and gives a conservative answer. The instantaneous center method credits the load-deformation behavior of the bolts for higher capacity but needs the AISC Manual coefficient tables, so this calculator uses the elastic method only.
Torsional shear is inversely proportional to the polar moment of inertia, which is the sum of squared distances from the group centroid. Spreading the pattern grows that sum quickly. Edge distance, member width and erection clearance still set practical limits.
No. Bolt shear is only one limit state. Bearing and tearout at the bolt holes, net section rupture, block shear, and the gusset or bracket plate itself all remain, so have a licensed structural engineer confirm the connection.