Steel connections transfer forces between beams, columns, braces, and other structural components. Their design affects structural performance, fabrication costs, installation speed, and future maintenance.

Welding, bolting, and riveting are three established methods of joining structural steel. Understanding their advantages and limitations helps project teams select suitable connections for different applications.

1. Welded Connections

What Is a Welded Connection?

In structural steel arc welding, an electric arc generates heat that locally melts the steel and a suitable filler material. The molten metal solidifies to form a permanent joint.

Advantages of Welded Connections

• Compact connection details: Welding can join components directly and reduce the need for overlapping plates or additional fasteners.

• No bolt holes at the welded joint: This avoids the net section reduction associated with fastener holes, although weld access openings and other details still require consideration.

• Versatile fabrication: Welding is suitable for built-up beams, box columns, stiffeners, and complex structural assemblies.

• Potential for sealed joints: Properly designed, continuous welds can provide sealed connections where required.

• Efficient repetitive production: Mechanized welding can improve productivity for suitable joint configurations.

Disadvantages of Welded Connections

• Residual stress and distortion: Uneven heating and cooling can cause shrinkage and changes in component geometry.

• Changes near the weld: Welding alters the microstructure of the adjacent steel. The effect depends on the material and thermal cycle; local brittleness is a potential risk, not an inevitable result. 

• Process and inspection requirements: Reliable results depend on appropriate joint preparation, welding procedures, competent personnel, and inspection.

• More demanding site conditions: Access, weather protection, and working position can complicate field welding.

• Difficult disassembly: Welded joints generally require cutting for separation or replacement.

Common Welding Processes

Manual Metal Arc Welding — MMA/SMAW

Also called stick welding, this process uses a consumable coated electrode. Portable equipment and flexibility make it useful for site work and restricted access. Its limitations include relatively low deposition rates and frequent electrode changes.

Submerged Arc Welding — SAW

SAW uses a continuously fed wire beneath a blanket of granular flux. It is commonly mechanized and suited to long welds in beams, girders, and plate assemblies. It requires suitable access and welding positions.

Gas Metal Arc Welding — GMAW/MIG/MAG

This process uses a continuous wire and an external shielding gas. It supports productive fabrication, but drafts can disturb the gas shield. Solid-wire GMAW does not produce the flux slag associated with stick welding or SAW. MIG uses inert shielding gases, while MAG uses active gases or mixtures. 

No welding process automatically produces a stronger joint than another. Process selection must consider steel grade, thickness, joint geometry, position, required properties, and the applicable welding procedure. 

2. Bolted Connections

What Is a Bolted Connection?

Bolted connections join steel components using bolts, nuts, and washers where specified. The bolts pass through prepared holes in members or connection plates.

Bolt strength and installation condition are separate considerations. A high-strength bolt does not automatically make a connection preloaded or resistant to slip.

Main Connection Types

Non-preloaded Connections

These connections do not rely on a specified bolt preload to resist slip. Under shear loading, force is generally transferred through bolt shear and bearing against the hole surfaces. They can be used in permanent structural connections where permitted by the design.

Preloaded Connections

Bolts are tightened using a specified procedure to develop a controlled clamping force. Where a connection is designed to resist slip, friction between the prepared contact surfaces transfers shear within the specified design conditions. Bolt installation and surface preparation are both critical. 

Advantages of Bolted Connections

• Efficient site assembly: Prepared components can be connected without field welding.

• No welding heat at the joint: Bolting avoids local welding distortion during installation.

• Easier disassembly: Connections can facilitate future alterations, maintenance, and component replacement.

• Suitable for prefabricated construction: Shop fabrication and site assembly can be coordinated through standardized connection details.

Disadvantages of Bolted Connections

• Reduced net section: Fastener holes remove material and must be considered in connection design.

• Additional components: Splice plates, end plates, or angles may increase material use and fabrication work.

• Fit-up requirements: Hole alignment, tolerances, and tool access need careful coordination.

• Installation control: Preloaded connections require appropriate tightening procedures and inspection.

• Movement and fatigue considerations: Slip, cyclic loading, and loosening risks depend on the joint design and installation; high-strength bolts alone do not eliminate them.

Bolted connections are widely used for site assembly. Preloaded arrangements are particularly relevant where relative movement or dynamic loading requires additional control.

3. Riveted Connections

What Is a Riveted Connection?

Traditional structural riveting uses a heated rivet inserted through aligned holes. Its projecting end is formed into a second head, securing the connected plates. Cooling causes the rivet to contract and clamp the assembly.

Advantages of Riveted Connections

• Permanent mechanical fastening: The formed heads secure the connected components.

• Ductile behavior: Suitable rivet materials and properly detailed joints can accommodate deformation.

• Value in restoration: Riveting can preserve the original appearance and construction method of historic steelwork.

Disadvantages of Riveted Connections

• Labor-intensive installation: Heating, handling, and forming rivets require specialist equipment and skills.

• Additional weight and material: Rivet heads, overlaps, and connection plates add to the assembly.

• Fastener holes: Like bolting, riveting reduces the net section of connected components.

• Difficult removal: Rivets usually must be drilled or cut out.

• Limited use in new structural steelwork: Welding and high-strength bolting have largely replaced traditional hot riveting.

Riveting remains relevant to certain historic bridge restoration projects, so describing it as completely obsolete would be inaccurate. 

Comparison of Steel Connection Methods

How to Choose the Right Steel Connection

The best connection method depends on the required forces, stiffness, fatigue performance, fabrication facilities, site conditions, and maintenance needs. Neither welded nor bolted connections should be classified as rigid or flexible solely by the joining method; the complete joint detail determines its behavior.

For project planning, compare the total cost of fabrication, transport, erection, inspection, and future alterations. Final connection details should follow the project specifications and be checked by the responsible structural engineer.

Planning a steel structure project? Contact us with your drawings and project requirements to discuss fabrication and connection options.