A gusset plate is a flat steel plate that joins two or more members meeting at a point. It is the piece that makes a truss node work: the diagonals, the chords and the verticals all bolt or weld to the same plate, and the plate is what actually transfers force between them.
It looks like the simplest part of the structure. It is not, and the consequences of treating it that way have been severe.
What the Plate Is Actually Doing
Think of the node as a small structure of its own. A diagonal in tension pulls on its bolt group; that force spreads into the plate, travels across it, and has to be delivered into the chord on the other side. Meanwhile a diagonal in compression pushes on its bolts and tries to buckle the free edge of the plate between members.
So a gusset plate has to be checked for several separate failure modes at once, and they do not all point the same way. Making the plate thicker helps with buckling but does nothing for a bolt group that is too small. Adding bolts helps the connection but can make the plate tear along the bolt line instead.
| Failure mode | What happens | What controls it |
|---|---|---|
| Bolt shear or weld failure | The fasteners themselves give way | Number, size and grade of bolts, or weld length |
| Bearing and tear-out | Bolts elongate the holes or rip out to the plate edge | Plate thickness, edge and end distance |
| Block shear | A chunk of plate tears out around the bolt group | Bolt layout and plate geometry |
| Gross and net section yielding | The plate stretches across its full or bolt-reduced width | Plate thickness and width |
| Compression buckling | The free edge of the plate waves out of plane | Thickness and unbraced length of the free edge |
The last one is the mode that gets missed. It is not obvious from a drawing that a flat plate can buckle, and it does not show up until the compression diagonal is carrying real load.
Why This Is Not a Detail to Eyeball
For decades gusset plates were often sized by proportion and experience rather than calculated for every mode, on the reasoning that the plate is generously sized compared with the members it joins. That assumption does not always hold, and where it fails the connection becomes the weakest part of an otherwise adequate structure.
The result is a structure whose capacity is set by a component nobody calculated. A truss designed so its members yield before its connections fail behaves very differently from one where the plate goes first: the first bends and warns, the second can let go without much notice.
Which is why connection design is now treated as engineering in its own right rather than shop detailing, and why a plate thickness on a drawing should trace back to a calculation.
Bolted or Welded
Both are normal, and the choice is usually about where the work happens. Welding is cheap in a shop and awkward in the air; bolting is quick on site and needs holes drilled accurately in advance.
Bolted gussets in steel buildings are governed by the Research Council on Structural Connections, which publishes the 2025 Specification for Structural Joints Using High-Strength Bolts (checked September 2026). That document is what sets how a bolted joint is designed, installed and inspected, including whether the joint is snug-tightened or pretensioned.
Welded gussets fall under the welding codes. The American Welding Society has authored more than 350 standards including D1.1, the Structural Welding Code for steel, which it calls one of the most-referenced codes in the world (checked September 2026). D1.1 covers the weld procedures, the qualifications and the inspection that a gusset weld has to satisfy.
A common arrangement uses both: the plate is shop-welded to one member and field-bolted to the others, which puts the fiddly work indoors and leaves a fast, verifiable connection for the erection crew.
Where You Meet Gusset Plates
Truss nodes. The original use, and still the most common: roof trusses, transfer trusses and bridge trusses all gather their members at plated joints.
Braced frames. Diagonal bracing in a steel building lands on a gusset at the beam-to-column corner. These plates get large, because the brace force is a substantial fraction of the whole building’s lateral load.
Beam splices and reinforcement. Plates also join beam segments or stiffen an existing member, which is related to how a flitch beam works: steel plate acting together with the members around it.
In all three the plate is sized against the members it connects, which is why the connection design starts from the member properties in something like our wide flange beam sizes chart, and why knowing which member is doing what matters before you detail the joint.
Frequently Asked Questions
How thick should a gusset plate be?
It comes out of the checks above: the force in each member, the bolt layout, the free edge length and the steel grade. There is no thickness that is safe by default, and matching the thickness of the members is a habit rather than a rule. A licensed structural engineer sizes it.
What steel are gusset plates made from?
Usually ASTM A36 or A572 plate. The grade matters to the calculation, so it is specified rather than assumed, and substituting a different grade changes the answer.
Can a gusset plate be repaired if it is corroded or cracked?
Often yes, by bolting or welding reinforcing plate to it, but the repair has to be designed. Section loss from corrosion reduces every one of the failure modes at once, and a plate that has lost thickness at its edge has lost buckling capacity fastest.
Why are gusset plates cut into odd shapes?
To reach every bolt group while using the least plate. The outline follows the members and the required edge distances, so the shape is an output of the layout. Trimming a plate on site to make it fit past an obstruction removes material the design was counting on.
Is a gusset plate the same as a connection plate?
Broadly, though gusset usually implies a node where three or more members meet, while a shear tab or connection plate joins just two. The design checks overlap heavily.
The Short Version
A gusset plate is a structural member, not a bracket. It has to be checked for bolt or weld capacity, bearing, tear-out, block shear, yielding on the gross and net sections, and buckling of its free edge, and those checks pull in different directions. It is designed, not proportioned by eye, and that design belongs to a licensed structural engineer.
Reference information only, not engineering advice. Disclaimer.