A gusset plate is a thick sheet of steel used for joining structural steel components. The gusset plate is installed at the intersection of two or more adjacent beams, chords, or columns. It may be fastened to each steel framing member using mechanical fasteners like bolts, or permanent bonds, such as welding. The gusset plates serves as both a method of joining the steel together and of adding strength and support to each joint.

Gusset plates can be found on many types of steel structures. A bridge gusset plate generally consists of a heavy-duty plate used at vehicle and pedestrian bridges. Different types of plates are also used to join steel while framing a building, or constructing a large piece of mechanical equipment. Smaller gusset plates can be found in truss construction. Depending on the size and function of the truss, the gusset plate may consist of a thin sheet of aluminum or a very heavy steel sheet.

Different types of gusset plate design can be characterized by size, shape, and fastening requirements. These plates often feature square or rectangular designs, but some more specialized models may even feature a triangular or custom shape to fit around nearby steel. Each plate may be designed for welding along different edges, or for both welding and bolting. Plate manufacturers typically pre-drill bolt patterns for easier installation in the field, though some may be delivered blank for maximum flexibility.

Structural engineers determine the required size and thickness of these plates, as well as the best fastening method. These calculations are made based on the force and loads applied to each plate, as well as the loads applied to nearby steel components. A gusset plate may be used as the sole fastening method between various beams and chords, or used in conjunction with bolts or welding. In some cases, the plate is added to the structure after completion to add strength or stiffness to joints. Gusset plates offer a fairly easy retrofit option for structures that cannot safely support the applied amount of force.

Gusset plates can be made from cold-rolled or galvanized steel, depending on the application. When the plates are used outdoors or around corrosive materials, they are often galvanized to prevent damage from rust. When these plates will be left exposed, they may be painted to match surrounding steel or other nearby fixtures. On some smaller exposed structures, gusset plates may be constructed from copper or aluminum to give a more attractive finish when minimal support is needed.