Project Delivery
Fabrication of Built-Up Tapered Steel Members
Fabrication of built-up members is the shop process of cutting steel plates, assembling them into I-shaped columns and rafters with webs that can taper along their length, welding flanges to webs, adding end plates and stiffeners, then cleaning, coating and marking each piece for site erection.
Key facts
- Webs and flanges are cut from plate so depth can vary along the member.
- Flange-to-web welds are commonly made by automated submerged arc or similar processes.
- End plates, stiffeners and clips are added according to shop drawings.
- Welding is carried out to qualified procedures under the governing welding code.
- Each piece is marked to match the erection drawings.
Why PEB frames use built-up members
Rolled sections have fixed depth and flange proportions. Built-up members allow the designer to place steel where bending forces are highest, typically deeper at the knee and shallower near the base and ridge. This tailoring is what makes a pre-engineered frame efficient.
Because each member is made from plate, web thickness, flange width and flange thickness can be selected independently. The engineering team chooses these proportions to the governing code, and fabrication turns them into finished pieces.
Plate cutting and preparation
Fabrication starts with plate cutting. Webs for tapered members are cut on numerically controlled thermal cutting machines, which follow the profile in the shop drawing. Flanges are cut as strips, often by multi-head cutting or shearing.
Cut edges are checked for dimension and quality, and any defects are removed before assembly. Material traceability is maintained so that plates can be linked back to mill documentation where required.
Assembly and welding
Web and flanges are assembled in a fitting machine or jig that holds them square and tack welds them. The member then passes to automated welding, where flange-to-web welds are made continuously on one or both sides as specified. Automated processes give consistent penetration and profile.
Welding follows qualified procedures and qualified welders or operators, under codes such as AWS D1.1, CSA W59, AS/NZS 1554.1 or the EN ISO 3834 quality framework. After main welding, end plates, stiffeners, purlin clips and bracing connections are fitted and welded manually or semi-automatically.
Straightening, drilling and dimensional control
Welding heat can distort a member. Flanges may be straightened mechanically, and members are checked for camber, sweep and flange tilt against fabrication tolerances. End plates are checked for flatness because they form bolted moment connections.
Holes are drilled or punched to shop drawings. Accurate hole location is essential: a misplaced hole in an end plate or purlin clip creates problems on site that are difficult to correct.
Surface treatment and marking
Finished members are cleaned by shot blasting or other methods to the specified preparation grade, then primed or painted according to the coating specification. Where galvanizing is specified, members are sent to a galvanizer with venting and draining holes provided.
Each piece receives a mark number matching the erection drawings. Clear marking speeds up sorting and erection on site and reduces the risk of installing the wrong member.
Points to confirm in the fabrication specification
- Welding code and quality requirements for the project.
- Steel grades for plate and the documentation required.
- Surface preparation grade and coating system.
- Fabrication tolerances and the reference standard.
- Inspection and testing scope for welds.
- Marking and piece identification method.
Frequently Asked Questions
Are PEB frames welded on site?
Usually not. Primary members are fully fabricated in the shop and connected on site with bolted end plate connections. This reduces site welding and improves quality control.
What is the difference between single-side and double-side web welds?
Flange-to-web welds can be made on one or both sides of the web. The choice depends on design forces, fatigue considerations such as crane loading, and the code requirements. The engineer specifies it.
Can built-up members be galvanized?
Yes, provided member size fits the galvanizing bath and the detailing includes venting and draining holes. Thin webs can distort, so this is reviewed during design.
Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.
