Connection design

Connections in a pre-engineered building

A defining feature of the PEB system is that all field connections are bolted. Members are fully welded in the factory – plates, stiffeners, clips and end plates – and on site they are joined with high-strength bolts. This makes erection fast and quality controllable, but places responsibility on connection design: connections are where load paths change direction and where most structural failures in light steel buildings originate. The main connection types are:

• Knee (column–rafter) and ridge connections: moment-resisting bolted end-plate connections.
• Rafter splices: flush or extended end plates at transport-length breaks.
• Column bases: pinned or fixed base plates and anchor bolts.
• Bracing connections: rod or angle bracing to frames via gusset plates, hillside washers or clips.
• Secondary connections: purlin and girt clips, flange braces, eave struts, crane brackets.

End-plate moment connection design

End-plate connections are designed for moment, shear and axial force. Design checks include bolt tension (with prying), end-plate bending using yield-line analysis, column flange bending and web yielding, stiffener requirements, panel-zone shear, compression-side web crippling and buckling, and weld strength between end plate and member.

In Eurocode design, joint stiffness must be compatible with the frame analysis assumption; a nominally rigid knee that is actually semi-rigid will increase frame deflection.

Practical design rules

• Use pretensioned (slip-critical or "TF") bolts where load reversal, fatigue or vibration occurs, e.g. crane buildings; snug-tight or pretensioned bearing bolts elsewhere as the code allows. See structural bolts and fasteners.
• Keep end-plate thickness and bolt diameter in proportion – thin plates with large bolts cause prying; very thick plates add cost and weld distortion.
• Standardise bolt sizes (e.g. M20/M24 or 3/4 in, 7/8 in, 1 in) across a project to simplify erection.
• Check flange-to-end-plate welds for the full flange force where the connection must develop the member; CJP or matched fillet welds as designed.
• Base plates: pinned bases with two or four anchor bolts are typical for PEB; fixed bases reduce drift but increase foundation size.
• Provide erection clearances and match-marking; slotted holes only where specified.

Secondary, bracing and special connections

Beyond the moment joints, a PEB contains hundreds of lighter connections that are standardised by the supplier but still designed:

Clip spacing, hole positions and bolt sizes are standardised so that the cold-formed members can be punched on the roll-forming line; any change to purlin depth or girt position therefore needs to be fixed before fabrication. Uplift and longitudinal bracing forces pass through these small connections, which is why they appear on the erection drawings with the same importance as the primary bolts.

Fabrication and inspection requirements

Connection welds are made under qualified procedures to AWS D1.1, AS/NZS 1554.1 or EN 1090-2 / EN ISO 3834 (see welding processes and consumables). End plates must be flat within tolerance so bolted faces bear; bolt holes are drilled or punched within code limits. Pretensioned bolts are installed and inspected by turn-of-nut, calibrated wrench, direct tension indicators or twist-off bolts per RCSC, AS 4100 / AS/NZS 5131 or EN 1090-2. World Steel fabricates to AS/NZS 5131 CC3, EN 1090-2 EXC3 and ISO 3834-2, and is accredited under IAS AC472 for metal building systems; connection design is part of its design service.

Software and documentation

PEB connection design is commonly automated within frame design software and then verified for unusual geometries with dedicated connection software or finite-element analysis. Each connection is identified on the erection drawings with bolt size, grade, quantity and tightening method; shop drawings show plate thickness, weld sizes and hole details. These are part of the design deliverables.