Structural Steel Fabrication
Also: structural steel, steel fabrication, structural fabrication, structural steel fabricator, beams and columns, miscellaneous metals, AISC certified fabricator, AWS D1.1, structural welding, steel detailing, platforms and mezzanines
Structural steel fabrication cuts, drills, fits and welds beams, columns, plate and tube into building frames, platforms and supports, to AISC and AWS D1.1.
336 shops tagged Structural steel among 2,961 welding and fabrication companies in the Noramark directory
Structural Steel Fabrication shops by state
A structural fabricator turns mill shapes into the members of a frame. Wide-flange beams and columns, channels, angles, hollow structural sections (HSS) and plate are cut to length on band saws, drilled or punched on beam lines, coped and profiled by plasma or oxy-fuel torch, fitted with connection plates, clip angles, stiffeners and base plates, welded, cleaned and coated. The work is driven by shop drawings: a detailer turns the engineer's design drawings into one drawing per piece plus erection drawings, and the engineer of record reviews and approves them before steel is cut.
In the U.S. the governing documents are the AISC Specification for Structural Steel Buildings (AISC 360), the AISC Code of Standard Practice (AISC 303), which sets tolerances and trade practice, and AWS D1.1, the structural welding code for steel. Shop welding is mostly flux-cored (FCAW), MIG (GMAW) and submerged arc (SAW), with stick (SMAW) common in the field. D1.1 allows prequalified welding procedures for common joints and requires welders qualified by test. Field connections are usually bolted with ASTM F3125 Grade A325 or A490 high-strength bolts, installed snug tight, pretensioned or slip critical as the drawings specify. Many project specifications require the fabricator to hold AISC certification, an audited quality program with separate categories for building and bridge fabricators.
Structural steel is built to construction tolerances, not machining tolerances. Members that frame to other steel are held to about ±1.5 mm (±1/16") in length up to 9 m (30 ft) and ±3 mm (±1/8") beyond that, and the mill shapes themselves vary in depth, flange width, camber and sweep within ASTM A6 limits. Connections are designed to absorb the variation: bolt holes are 2-3 mm (1/16-1/8") larger than the bolt, and slots and shims take up the rest. A surface that needs machine accuracy, such as an equipment mounting pad or a bearing seat, is machined after welding and has to be called out.
The same shops build what the trade calls miscellaneous metals: stairs, handrails, ladders, platforms, mezzanines, lintels, embeds, equipment supports, pipe racks and skids. Typical finishes are a shop primer over a cleaned surface, a blast and multi-coat paint system, or hot-dip galvanizing for exterior and corrosive service. Erection is done by the fabricator's own crew or by a separate erector, and the fabricator sequences deliveries to match it.
At a glance
| Typical tolerances | Fabrication tolerances follow the AISC Code of Standard Practice (AISC 303) and AWS D1.1. Length of members that frame to other steel: ±1.5 mm (±1/16") up to 9 m (30 ft) and ±3 mm (±1/8") over that; ±0.8 mm (±1/32") on members with both ends finished for bearing. Straightness of compression members within 1/1000 of the length between supports. Hole locations within a connection are typically held to about ±1.5 mm (±1/16"), in holes 2-3 mm (1/16-1/8") larger than the bolt. Mill shapes vary in depth, flange width, camber and sweep within ASTM A6 limits. Anything tighter is machined after welding and must be called out on the drawings. |
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| Size limits | Shipping limits a piece more than the shop does. Loads up to about 14-16 m (48-53 ft) long, 2.6 m (8.5 ft) wide and roughly 20 tons travel on a standard flatbed without permits, with limits that vary by state; longer, wider or heavier pieces ship under permit or are spliced in the field. Rolled wide-flange shapes run up to about 1,100 mm (44") deep, and deeper girders are built up from plate. Shop cranes of 5-25 tons are typical. Hot-dip galvanizing limits a piece to the galvanizer's kettle, commonly 9-18 m (30-60 ft) long. Small fabricators concentrate on stairs, rails and platforms; large ones run thousands of tons on a single project. |
| Surface finish | Steel arrives from the mill with mill scale. Surface preparation is specified by SSPC standard: SP 2 hand-tool or SP 3 power-tool cleaning under a basic shop primer, SP 6 commercial blast for most paint systems, and SP 10 near-white blast for high-performance coatings. Finishes are a shop primer, a multi-coat paint system, hot-dip galvanizing to ASTM A123, or galvanizing plus paint (a duplex system). Steel that will be fireproofed or encased in concrete, and the contact surfaces of slip-critical joints, are often left unpainted. Architecturally exposed structural steel (AESS) is ordered by category, with tighter fit-up, dressed welds and controlled surface quality at added cost. |
| Lead time | Small miscellaneous jobs such as stairs, rails, platforms and equipment supports in about 2-6 weeks. Building frames typically take 8-16 weeks from award to delivery: 2-6 weeks for detailing and approval of shop drawings, then material procurement and fabrication, and longer for large or complex projects. Mill rolling schedules for uncommon shapes, approval turnaround and galvanizing (add 1-2 weeks) are the usual delays; shapes in service-center stock shorten the schedule. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Wide-flange shapes are ASTM A992, with a 345 MPa (50 ksi) minimum yield. Plate, bars, angles and channels are A36 (250 MPa, 36 ksi) or A572 Grade 50. Square, rectangular and round HSS are A500 Grade B or C, or A1085; pipe is A53 Grade B. Weathering steel (A588, and A847 for HSS) is used unpainted for bridges and exposed architectural work. Bolts are ASTM F3125 Grades A325 and A490, and anchor rods are F1554. Filler metals match the base metal, most often E70-class electrodes. High-strength quenched and tempered plate such as A514 needs controlled heat input and qualified procedures. Stainless and aluminum structures are built under different codes (AWS D1.6 and D1.2) and usually by different shops.
What drives the cost
- Tonnage, and the mill or service-center price of steel, which moves with the market
- Connections: fabrication labor follows the number of pieces, holes, copes, stiffeners and welds more than the weight
- Weld type: fillet welds are cheap; complete-joint-penetration groove welds need beveling, more passes and often ultrasonic testing
- Detailing and engineering: shop drawings, connection design delegated to the fabricator, model coordination
- Coating: shop primer, blast and multi-coat paint, or hot-dip galvanizing priced by weight
- Quality requirements: AISC certification, special inspection, nondestructive testing, AESS category, seismic or bridge provisions
- Freight and erection: piece size, permits, site access and crane time
When to use it
- Building and mezzanine frames, platforms, stairs, handrails, ladders and catwalks
- Equipment supports, pipe racks, skids, crane runways and heavy frames
- Trusses, canopies, lintels, embeds and other miscellaneous metals for construction
- Projects whose specification calls for AISC certification, AWS D1.1 welding and mill test reports
- Heavy weldments from plate and shapes where construction tolerances are acceptable
When not to
- Precision weldments and machine frames that need ±0.25 mm (±0.010"): use a fabricator that machines after welding
- Sheet metal under about 5 mm (3/16"): enclosures, guards and brackets belong with a sheet metal fabricator
- Stainless or aluminum structures, unless the shop is set up for them and for AWS D1.6 or D1.2
- Pressure vessels, which are built to the ASME Boiler and Pressure Vessel Code by shops that hold the code stamp
- Repetitive light profiles at volume: roll forming or stamping costs less per piece
Design tips
- Use shapes and sizes that service centers stock, and repeat member sizes and connection types; variety costs more than weight.
- Prefer shop-welded, field-bolted connections; field welding is slower, depends on the weather and needs inspection on site.
- Size fillet welds to the load and use them wherever they work; an 8 mm (5/16") fillet is the largest most shops place in a single pass, and complete-joint-penetration welds cost several times more.
- Name the codes and the materials: AISC 360 and 303, AWS D1.1, ASTM A992 for wide flange, A500 for HSS, A36 or A572 Grade 50 for plate, and the bolt grade and installation method.
- State the coating system and the surface preparation, and mark the surfaces that stay bare: slip-critical contact surfaces, field-weld areas and steel that gets fireproofing.
- For galvanized work, design vent and drain holes into closed sections and keep each piece within the kettle size.
- Send the structural drawings or model, the specification section and the delivery sequence, say who erects, and ask what piece sizes the site can receive.
- Call out anything tighter than AISC tolerances explicitly, and expect it to be machined after welding.
Tools and guides
Frequently asked questions
- What is AISC certification?
- A quality certification from the American Institute of Steel Construction. An independent auditor checks the fabricator's quality management system, procedures, personnel, equipment and records, with separate categories for building fabricators, bridge fabricators and erectors. Many project specifications and public owners require it. It certifies the company's quality system, not individual welders, who are qualified under AWS D1.1.
- What steel grades are used for structural steel?
- ASTM A992 for wide-flange beams and columns (345 MPa, 50 ksi minimum yield), A36 or A572 Grade 50 for plate, angles and channels, A500 Grade B or C for square, rectangular and round HSS, and A53 Grade B for pipe. Weathering grades such as A588 are used unpainted. The mill supplies a certified material test report for each heat.
- Should structural connections be welded or bolted?
- Usually both: welded in the shop and bolted in the field. Shop welding is done under cover, with the work positioned for the welder, and is easy to inspect. Field bolting is fast, works in most weather and needs no welding inspection on site. Field welding is kept for connections where the design requires it.
- How much does structural steel fabrication cost?
- Fabricated steel is usually priced per ton, delivered or erected, and the price moves with the steel market and the complexity of the work. Simple beam-and-column framing costs far less per ton than stairs, rails and other connection-heavy miscellaneous metals, where labor dominates. Ask for the price broken out into material, fabrication, coating, freight and erection so that quotes can be compared.
- What is the difference between structural steel and miscellaneous metals?
- Structural steel is the load-carrying frame: beams, columns, braces, trusses and their connections. Miscellaneous metals are the other fabricated steel items on a project, such as stairs, handrails, ladders, gratings, lintels, bollards and embeds. Many fabricators do both, and some specialize in one.
