A Nelson stud is a short steel pin that gets welded to a steel beam and then embedded in concrete, creating a mechanical bond between the two materials. It functions as a shear connector, meaning it transfers horizontal forces (shear) between a steel beam and a concrete slab so they act as a single composite unit rather than two separate layers. You’ll find Nelson studs in bridge decks, composite floor systems in buildings, and other structures where steel and concrete need to work together.
How Nelson Studs Work
Steel and concrete are strong in different ways. Steel handles tension well, and concrete handles compression well. When you pour a concrete slab on top of a steel beam, though, the two materials can slide against each other under load. That sliding weakens the structure significantly because the beam and slab aren’t sharing the work.
Nelson studs solve this by physically locking the concrete to the steel. The stud is welded vertically to the top flange of a steel beam, with its head sticking up into the concrete slab. When a load pushes the concrete sideways relative to the steel, the stud resists that movement. Hundreds of these studs along a beam turn what would be two independent layers into a composite section that’s much stiffer and stronger than either material alone. This composite action lets engineers use smaller, lighter steel beams while still meeting load requirements.
Sizes and Materials
Nelson studs are manufactured from cold-drawn steel, specifically ASTM A29 Grades 1010 through 1020. They come in six standard diameters: 3/8, 1/2, 5/8, 3/4, 7/8, and 1 inch. The most common size for building construction is the 3/4-inch diameter stud, while bridge projects often use 7/8-inch studs for higher shear capacity.
Each stud has a flat, round head slightly wider than the shaft. That head is important because it provides mechanical anchorage inside the concrete, preventing the slab from lifting off the beam (a force called uplift). The length of the stud varies depending on the thickness of the concrete slab it will be embedded in, but it must extend far enough into the slab to develop its full strength.
Nelson studs are classified as Type B studs under the American Welding Society’s Structural Welding Code (AWS D1.1), and installation must also comply with AISC 360, the steel construction specification published by the American Institute of Steel Construction.
The Stud Welding Process
Nelson studs aren’t attached with conventional stick or MIG welding. They use a specialized process called drawn-arc stud welding, which fuses the entire base of the stud to the steel beam in less than a second. Here’s how it works:
- Loading: The stud is placed into the chuck of a stud welding gun, and a ceramic ferrule (a small cylindrical collar) is fitted around the base of the stud.
- Arc strike: The gun is pressed against the steel surface and triggered. It lifts the stud slightly off the workpiece, creating an electrical arc that melts both the end of the stud and the surface of the steel beneath it.
- Plunge: After a precisely timed interval, the gun plunges the stud down into the pool of molten metal. The weld solidifies almost instantly, forming a full-penetration connection with a visible fillet (a rounded ring of metal) around the base.
The entire lifting and plunging action happens inside the ceramic ferrule, which plays several roles at once. It contains the molten weld metal like a mold, keeping the fillet neat and uniform. It vents gases produced during welding, such as oxides and hydrocarbons, that would otherwise weaken the joint. It limits the volume of air around the weld zone so the flux on the stud tip can effectively remove oxygen. And it shields the operator from the intense ultraviolet light the arc produces. After welding, the ceramic ferrule is knocked off and discarded.
A skilled operator can weld several hundred studs per day. The process is fast enough that it’s typically done on the construction site, with the stud gun powered by a portable welding unit. Quality is verified through bend tests: a random sample of studs is bent 15 degrees from vertical using a hammer or pipe. If the stud bends without cracking at the weld, the batch passes.
Where Nelson Studs Are Used
The most common application is composite steel floor decks in commercial buildings. Steel beams support corrugated metal decking, and Nelson studs are welded through the decking into the beam below. When concrete is poured over the decking, the studs embed in the slab and tie everything together. This composite floor system is standard in office towers, hospitals, parking garages, and similar structures.
Bridge construction is the other major use. Nelson studs connect steel girders to reinforced concrete bridge decks, allowing the deck to act as the top flange of the girder. This dramatically increases the load-carrying capacity of the bridge without adding significant weight. Highway overpasses, pedestrian bridges, and large-span road bridges all rely on this type of composite design.
You’ll also find Nelson studs in industrial settings like power plants and petrochemical facilities, where steel plates need to be anchored to concrete foundations or where concrete linings are attached to steel shells.
Why the Name “Nelson”
The name comes from the Nelson Stud Welding company, which pioneered the drawn-arc stud welding process and became so dominant in the market that “Nelson stud” became a generic industry term, similar to how “Kleenex” is used for tissues. The brand is now part of Stanley Engineered Fastening. In practice, engineers and ironworkers use “Nelson stud,” “shear stud,” and “headed stud” interchangeably, though “Nelson” specifically refers to studs made by or to the specifications of that manufacturer.