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AASHTO Requirements for Gusset Plate

Gusset plates are steel plates that connect columns to beams and girders. Fasteners like bolts, rivets or welding or all of three can be used to fasten gusset plates to other members. Gusset plates not only serve as a method of joining steel members together but they also strengthen the joint. They can be used in bridges and buildings along with other structures.

The lateral dimensions of a gusset plate are determined principally by the fastener requirements of the members, which leaves only  the thickness to be based on other considerations.
Gusset Plate Connecting Girders
According to the AASSHTO specifications, “Gusset plates shall be of ample thickness to resist shear, direct stress, and flexure, acting on the weakest or critical section of maximum stress.” This is all very good, but the only practicable method of estimating these stresses is based on the assumption that the elementary formulas for beams apply, and these formulas are valid only for beams whose span is more that twice the depth and at cross sections not closer to concentrated loads than about half the depth.

The ordinary gusset plate falls considerably short of these requirements, so the results
obtained by the application of beam formulas are of questionable value and may be misleading.

In case of truss, Compressive stresses may develop parallel to and at the edge of gusset plates. This is because deflection of a truss tends to change the angles between its members. Therefore, the width of the top edge must not be too large, compared with the thickness, or the plate may buckle. Bending of this kind is called local buckling. The AASHTO specifications require than an unsupported edge of a gusset plate be stiffened if it is longer than 11,000/√Fy.psi times the thickness.

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