Manufacturing Expertise

Structural steel fabrication is where load-bearing designs become physical reality. A machine base that holds a 2,000-pound gantry. A custom equipment frame that survives a decade of daily industrial use. A weld-fabricated support structure that must not deflect more than 0.010″ under load.

Getting structural fabrication right requires more than cutting and welding steel. It requires understanding material grades, joint design, welding procedure, heat distortion management, and inspection standards, before the first arc is struck. This guide covers the full picture.

For a complete overview of metal fabrication processes including structural work, see our expert guide to custom metal fabrication.

What Is Structural Steel Fabrication?

Structural steel fabrication is the process of cutting, fitting, welding, and finishing steel structural members, plate, tube, angle, channel, I-beam, and wide flange sections, into load-bearing assemblies. The finished product may be a machine base, equipment frame, conveyor support, industrial skid, mezzanine structure, or any weld-fabricated assembly that carries significant mechanical or structural load.

Structural fabrication differs from sheet metal fabrication in material thickness, load requirements, and the role of welding. Where sheet metal fabrication uses thin stock and moderate joining, structural fabrication uses heavy plate and structural profiles where the weld joints are the primary load path. Joint design, weld procedure, and inspection are correspondingly more rigorous.

What Is the Difference Between Structural Steel and Fabricated Steel?

Structural steel refers to steel shapes and grades produced to structural specifications, ASTM A36, A500, A572, designed to carry predictable loads in construction and industrial applications. Fabricated steel is the result of taking structural steel stock and processing it into a specific assembly through cutting, drilling, fitting, and welding.

In practice: the I-beam stock you buy from a service center is structural steel. The custom equipment frame your fabrication shop welds from that stock, machined to final dimensions and inspected to AWS standards, is structural steel fabrication. The distinction matters because fabrication introduces variables, heat input, distortion, residual stress, joint quality, that the base material alone does not.

What Steel Grades Are Used for Structural Steel Fabrication?

ASTM A36

A36 is the workhorse of structural fabrication. Yield strength of 36 ksi, tensile strength of 58–80 ksi, excellent weldability, and wide availability in plate, bar, angle, and channel. Per ASTM A36 specification, it is the standard grade for machine bases, frames, structural supports, and weldments where high strength is not required.

ASTM A500

A500 covers cold-formed structural tubing (round, square, and rectangular HSS). Grade B (42 ksi yield) and Grade C (46 ksi yield) are standard for structural tube and pipe applications. A500 tube is common in machine frames, conveyor structures, and equipment skids where closed sections provide good torsional stiffness with lower weight than equivalent open sections.

ASTM A572 Grade 50

A572-50 provides 50 ksi yield strength with good weldability, the next step up from A36 for applications where higher strength allows thinner sections and lower weight. Used when structural analysis drives higher-grade steel to meet deflection or stress requirements without adding material.

Stainless Structural Grades

304 and 316 stainless structural sections are specified for food processing, pharmaceutical, and chemical environments where carbon steel would require ongoing corrosion protection. Higher material cost is offset by elimination of painting or coating requirements and longer service life in corrosive environments.

What Is the Process of Structural Steel Fabrication?

A structural fabrication job moves through six stages:

• Drawing review and DFM: Review fabrication drawings for weld access, joint type, inspection requirements, and fit-up clearances. Flag issues before cutting begins.
• Material procurement and certification: Source structural steel with mill certs confirming grade, heat number, and mechanical properties. Verify incoming material against certs before cutting.
• Layout and cutting: CNC plasma cutting, laser cutting, or saw cutting of plate and structural sections to length. Drill or punch connection holes. Mark fit-up references.
• Fit-up and fixturing: Assemble members in fixtures or on a flat table to control geometry before welding. Critical dimensions are set and checked at fit-up, not after welding.
• Welding: Execute weld procedure per applicable standard (AWS D1.1 for structural steel). Manage heat input and weld sequence to minimize distortion. Preheat as required for material thickness and grade.
• Post-weld inspection and correction: Visual inspection, dimensional verification, and NDT as specified. Correct any non-conformances before finishing.

How Does Welding Work in Structural Steel Fabrication?

Welding is the primary joining method in structural fabrication. Most structural steel welding follows AWS D1.1 Structural Welding Code, Steel, which governs joint design, weld procedure qualification, welder qualification, and inspection requirements.

Key welding considerations for structural fabrication:

• Joint type selection: Fillet welds for most structural connections; full-penetration groove welds for moment connections and high-load joints where the weld must develop the full strength of the base material.
• Weld sequence: Welding sequence affects distortion. Back-step welding, balanced welding (alternating sides), and pre-set camber are standard techniques to control final geometry.
• Preheat: Thick plates and high-carbon steels require preheat to slow cooling rate and prevent hydrogen-induced cracking. AWS D1.1 specifies minimum preheat by material grade and thickness.
• Heat input control: Excessive heat input causes excessive distortion and can degrade mechanical properties in heat-affected zones. Welding procedure specifications define amperage, voltage, and travel speed limits.

Rich Neal, Director of Manufacturing, on what integrated fabrication and machining capability makes possible:

“We got full capabilities to make anything that we need. We got full 5-axis milling capability, two 3-axis mills, a full 4-axis live tooling lathe with a bar feeder, so it allows us to do pretty much anything that we need to get done here.”   Rich Neal, Director of Manufacturing, Bravo Team

Quality Control and Inspection for Structural Steel Fabrication

Quality control in structural fabrication is a staged process. By the time the assembly is complete, the most expensive errors have already been made, or hopefully prevented.

• Incoming material verification: Mill cert review and dimensional verification of structural stock before cutting.
• Fit-up inspection: Dimensional check of assembled members before welding begins. Catching misalignment at fit-up costs minutes. Catching it after welding costs hours.
• Visual weld inspection (VT): All welds inspected visually per AWS D1.1 criteria: size, length, profile, undercut, overlap, and surface discontinuities.
• Dye penetrant testing (PT): Surface-breaking cracks and porosity on non-magnetic materials and complex geometries. Common on stainless structural components.
• Magnetic particle testing (MT): Near-surface discontinuities in ferromagnetic materials. Faster than PT for carbon steel structural welds.
• Ultrasonic testing (UT): Subsurface weld discontinuities in full-penetration groove welds. Specified for moment connections and structural joints where internal quality cannot be verified visually.
• Final dimensional verification: Overall assembly dimensions, bolt hole locations, and critical interface features measured against drawing callouts before delivery.

Build-to-Print Structural Fabrication

Structural fabrication is frequently build-to-print work: the design is validated, the drawing package is complete, and the requirement is a fabrication partner who can execute precisely and deliver on time. For what to expect from a build-to-print engagement, see our guide on build-to-print manufacturing.

When design is still in development, structural fabrication benefits from early fabricator involvement. Structural weld joint design, access for inspection, fit-up sequence, and post-weld machining requirements all affect fabricability. At Bravo Team, our engineering team and fabricators review structural designs together, manufacturability issues surface at the drawing stage, not at fit-up.

“Our machinists have decades of experience. Being able to hear their input and learn from that is very valuable, it allows us to be efficient with our time and learn as we design new parts for a variety of different industries.”   Gregory Helfrich, Mechatronics Engineer, Bravo Team

Welding Distortion Control in Structural Steel Fabrication

Thermal distortion is the most common quality problem in structural steel fabrication. When weld metal cools and contracts, it pulls the base material toward the weld. In a large structural assembly, this distortion accumulates across every weld joint and can shift overall dimensions significantly from the design intent.

Standard distortion control techniques:

• Pre-setting: Set members slightly out of position before welding so that distortion during welding brings them to the correct final geometry. Requires experience and knowledge of how a specific joint design will move under heat input.
• Balanced welding: Weld alternating sides of symmetric assemblies so thermal contraction forces cancel rather than accumulate. A column welded on one side only will bow toward that side; welding both sides alternately keeps it straight.
• Back-step welding: Weld in short segments in the direction opposite to the overall weld progression. Reduces the length of HAZ at any one time and limits thermal gradient across the base material.
• Fixturing: Fixture the assembly in its correct geometry and tack it before welding. Strongbacks, clamps, and tack welds at close intervals limit movement during welding. Release fixtures only after full cool-down.
• Post-weld straightening: Thermal straightening, applying controlled heat to a distorted section, can correct distortion after welding. Mechanical straightening (pressing or rolling) is used on plate and structural sections. Both are secondary operations that add cost and should be designed out where possible.

Secondary Machining of Structural Weldments

Welded structural assemblies that require precision mating surfaces, precise hole patterns, or flat reference planes typically undergo secondary machining after fabrication. This two-step approach combines the efficiency of fabrication for the structural body with the precision of machining for critical interfaces.

Common secondary machining operations on structural weldments:

• Milling weld-fabricated base plates flat for machinery mounting, typically to 0.003″ flatness over the full plate area
• Drilling and tapping precise bolt patterns on structural members after assembly, positioning features off a machined reference rather than off the weld-distorted structure
• Boring precision holes in welded tube or structural section for bearing and bushing fits
• Machining weld joint faces to exact size when as-welded dimensions do not meet the specification

At Bravo Team, this handoff between fabrication and machining happens within the same facility. The fabrication team completes the structural weldment; the machine shop team takes it from there for secondary operations, with both teams reviewing dimensional requirements against the drawing before the first cut. That coordination eliminates the communication gaps and schedule delays that come with sending a welded assembly to a separate machine shop.

Steel Fabrication Services: What Full-Scope Capability Looks Like

A full-service structural steel fabrication capability covers more than cutting and welding. Complete steel fabrication services for custom equipment include:

• Material procurement with certified mill documentation (ASTM compliance, heat number, material cert)
• CNC plasma and laser cutting of plate and sheet to profile
• Structural saw cutting and cold saw for tube, channel, angle, and wide flange sections
• CNC drilling and punching for connection patterns and hardware locations
• Fit-up and fixturing prior to welding
• MIG and TIG welding per applicable AWS standards
• Post-weld inspection: visual, dye penetrant, magnetic particle, ultrasonic as specified
• Secondary CNC machining for precision interfaces
• Finishing: powder coat, paint, primer, galvanize coordination as specified
• Final dimensional inspection against drawing callouts
• Delivery or system assembly at Bravo Team facility

“We are solely focused on getting things done efficiently for the engineers to get things done on time in the most effective way.”   Rich Neal, Director of Manufacturing, Bravo Team

Frequently Asked Questions About Structural Steel Fabrication

What is fabrication of structural steel?

Structural steel fabrication is the process of cutting, drilling, fitting, welding, and finishing structural steel sections, plate, tube, angle, channel, wide flange, into load-bearing assemblies. It produces machine bases, equipment frames, industrial structures, and weld-fabricated assemblies designed to carry mechanical or structural loads.

What is the difference between structural steel and fabricated steel?

Structural steel refers to steel stock produced to structural specifications (ASTM A36, A500, A572) designed for load-bearing applications. Fabricated steel is the result of processing structural steel stock into a specific assembly through cutting, fitting, and welding. All structural fabrication uses structural steel, but not all structural steel is fabricated, it may be used as-rolled or as-extruded without secondary processing.

What type of steel is most commonly used for structural fabrication?

ASTM A36 plate, bar, and angle is the most common grade for general structural fabrication. A500 Grade B and C tubing is standard for machine frames and equipment structures using HSS sections. A572 Grade 50 is specified when higher yield strength is required to reduce member size or weight.

What does a structural steel fabricator do?

A structural steel fabricator receives engineering drawings and produces finished structural assemblies from raw steel stock. The scope includes material procurement with certified mill documentation, CNC cutting and drilling, fit-up and fixturing, welding per applicable codes, post-weld inspection (visual, NDT as specified), finishing, and dimensional verification before delivery.

What are the quality standards for structural steel welding?

AWS D1.1 Structural Welding Code, Steel is the primary standard governing structural steel welding in the United States. It specifies joint design, weld procedure qualification, welder qualification, and inspection requirements. See the American Welding Society for full standard documentation.

Choosing a Structural Steel Fabrication Partner

Bravo Team’s fabrication team handles structural steel fabrication from drawing review through delivery, with machining, welding, and inspection under one roof. For a full framework on evaluating fabrication partners, see how to choose a metal fabrication company.

Structural Fabrication That Meets Engineering Specifications

Bravo Team’s in-house fabrication shop handles structural steel fabrication alongside CNC machining, sheet metal, and full assembly, with 112 years of collective machining experience and our engineering team available throughout the process. From machine bases to custom equipment frames, we execute structural fabrication to spec and on schedule.

Ready to discuss a structural fabrication project? Talk to a machinist today.