Engineering & Design
Connection Design in Pre-Engineered Buildings
Connection design in pre-engineered buildings is the engineering of the joints that hold the structure together, including bolted end plate moment connections at knees and ridges, rafter splices, base plates, bracing connections and purlin and girt attachments, so that forces pass safely between members.
Key facts
- Most field connections in a PEB are bolted, while shop connections are welded.
- Bolted end plate moment connections make rigid frames quick to erect.
- Bolt type and installation method, snug-tight or pretensioned, are part of the design.
- Prying action, plate bending and weld size all affect end plate capacity.
- Seismic regions may require special connection detailing and testing-based rules.
Which connections are typical in a metal building
The knee joint between column and rafter and the ridge joint between two rafters are usually bolted end plate moment connections. Long rafters are split into shippable lengths and joined with end plate splices. Columns connect to foundations through base plates and anchor rods.
Secondary members attach with bolted clips welded to the frames, and bracing rods or angles connect through gusset plates or brace clips. Each connection is designed for the forces from the analysis and detailed so that it can be fabricated accurately and bolted up on site.
How bolted end plate moment connections work
In an end plate connection, a plate welded to the end of a member is bolted to a matching plate or column flange. Bending moment is carried by tension in bolts near one flange and compression bearing at the other, while shear passes through the bolts.
The design checks bolt tension and shear, plate bending including prying action, the welds joining plate to member, and the local strength of the column web and flanges. Stiffeners may be added where the column cannot resist the concentrated forces. The bolt arrangement and plate thickness are optimized together.
How US and Canadian codes treat connections
In the United States connections are designed to AISC 360, and AISC publishes design guidance for metal building end plate connections. Bolts are installed to the RCSC Specification for Structural Joints, which defines snug-tight, pretensioned and slip-critical joints. Welding follows AWS D1.1, and in seismic regions AISC 341 and the related prequalified connection standard AISC 358 may apply.
In Canada CSA S16 governs connection design, including seismic requirements in its seismic clauses. Welding follows CSA W59, and fabricators of welded structures are expected to operate under CSA W47.1.
How Australian/NZ and European codes treat connections
In Australia AS 4100 sets the rules for bolts, welds and connection elements, and AS/NZS 1554.1 covers structural welding. AS/NZS 5131 sets requirements for fabrication, bolt installation and tensioning. New Zealand applies NZS 3404 for steel design with the same welding and fabrication standards.
In Europe EN 1993-1-8 covers the design of joints, including a component method that models a joint by the strength and stiffness of its parts. Joint stiffness is classified as rigid, semi-rigid or pinned, which affects frame analysis. Bolting and welding execution follow EN 1090, and welding quality follows EN ISO 3834.
Detailing for fabrication and erection
Good connections are designed for constructability as well as strength. Clear bolt access, consistent bolt sizes, sensible tolerances and slotted holes where movement is required make erection faster and safer.
Shop drawings show each connection, its bolts and any pretension requirement. All connection designs are confirmed by the project engineer to the governing code.
Connection points to confirm
- Bolt standard, grade and whether any joints require pretension or slip resistance.
- Seismic detailing requirements at frames and bracing.
- Fabricator welding procedures and qualifications for the code in force.
- Inspection method for bolt pretension on site.
- Finish of bolts to match the frame coating and environment.
- Any connection to existing or third-party structures.
Frequently Asked Questions
Why are pre-engineered frames bolted rather than welded on site?
Bolting is faster, needs less specialist labor and is easier to inspect in the field. Welding is done in the shop under controlled conditions, which gives consistent quality.
Do all bolts in a PEB need to be fully tensioned?
No. The design specifies which joints are snug-tight and which must be pretensioned. Moment connections and certain bracing joints commonly require pretension, depending on the code and loads.
Can I replace a specified bolt with a different grade?
Only with written approval from the engineer. Bolt grade affects strength, ductility and installation method, so substitution can change the safety of the connection.
Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.
