Bolted end-plate connections

Definition and function

A bolted end-plate connection joins two members of the primary frame through steel plates welded to their ends and bolted together on site. In a pre-engineered building end plates are used at the knee (column to rafter), at the ridge (rafter to rafter) and at field splices within long rafters and columns. They are moment-resisting: they transfer bending moment, shear and axial force, so the frame behaves as a continuous portal.

The principal advantage is that all welding is done under controlled shop conditions and the site work is reduced to bolting. This is a key reason PEB frames erect quickly and consistently.

Extended end-plate moment connection with bolt rows above and below the beam flange — Extended end-plate moment connection at a rafter knee.

Connection types and where they sit in the load path

The connection carries the frame moment across the joint: the tension flange pulls on the bolts nearest to it, while the compression flange bears through the plates. The rafter delivers its moment and shear through the knee into the column.

End-plate configurations
Type	Description	Typical use
Flush end plate	Plate within beam depth; bolts inside flanges	Ridge and splices with moderate moment
Extended end plate	Plate extends beyond tension flange with outer bolt row	Knees and highly loaded splices
Stiffened extended	Extension stiffened by a rib plate	High moments, seismic frames
Multiple-row	Two or more bolt rows at each flange	Deep haunches with large moments

Where end-plate joints occur in a PEB frame
Joint	Typical arrangement	Comment
Knee – vertical end plate	Rafter end plate bolted to the column flange or column cap end plate	Most common; column top often stiffened
Knee – horizontal end plate	Rafter seated on a horizontal plate on top of a deep column	Used where the haunch is part of the column piece
Ridge	Two rafter end plates bolted at the apex	Moment usually lower than at the knee; flush plates common
Rafter field splice	Flush or extended plates at transport breaks	Located where moment is low and within shipping length
Column splice	End plates or bolted flange cover plates	Tall columns, stepped crane columns
Interior column cap	Rafter bottom flange bolted to a column cap plate	Bearing and shear connection in multi-span frames

Typical plate, bolt and weld sizes

Indicative sizes (design governs)
Item	Typical range
End-plate thickness	12–40 mm
Bolt diameter	M16–M30 (5/8"–1-1/4")
Bolt grade	ASTM F3125 A325/A490; property class 8.8 or 10.9
Flange-to-plate weld	Fillet or complete-joint-penetration per design
Web-to-plate weld	Fillet welds, both sides

For bolt and fastener material see structural bolts and cladding fasteners. End plates are usually cut from 345–355 MPa plate; through-thickness properties may need attention for thick plates in highly loaded joints.

Design considerations

US: AISC Design Guide 39 (End-Plate Moment Connections, 2023) consolidates and replaces the earlier Design Guides 4 and 16; AISC 358 covers prequalified end-plate connections for seismic moment frames.
Europe: EN 1993-1-8 component method, including T-stub analysis and rotational stiffness classification.
Australia / NZ and Canada: AS 4100:2020 and CSA S16-19 member and connection provisions, with industry design guides.
Prying action on thin plates increases bolt tension – thicker plates or stiffeners reduce it.
Panel zone of the column at the knee may need diagonal or horizontal stiffeners.
Bolt pretension: the design states whether bolts are snug-tight or pretensioned. Moment end plates are typically pretensioned under the RCSC Specification.

Connection design is covered in more detail under connection design.

Fabrication and installation

World Steel cuts and drills end plates on CNC lines, welds them square to the member axis (or at the roof slope for knees and ridges) and checks flatness after welding, because distortion causes gaps on site. Faying surfaces are masked or coated as specified when slip-critical joints are required.

Bring plates together and insert all bolts with washers as detailed.
Snug-tighten bolts in a pattern from the centre outward until the plates are in firm contact.
Pretension by turn-of-nut, calibrated wrench, direct tension indicators or twist-off bolts where required.
Mark tightened bolts and record inspection.

Common mistakes and quality checks

Gaps between plates from weld distortion – check plate flatness in the shop.
Wrong bolt grade or length; mixing grades between connections.
Galvanised or lubricated bolts reused after pretensioning.
Paint on faying surfaces of slip-critical joints not matching the specified slip class.
Bolts left snug-tight when pretension was required – verify with inspection records.

Normas por región

Región	Norma	Alcance
United States	AISC 360-22 / AISC DG 39 / RCSC	Connection design, end-plate design guide and high-strength bolt specification
Canada	CSA S16-19	Bolted connections and pretensioning
Australia / NZ	AS 4100:2020 / AS/NZS 5131	Connection design and bolt installation
Europe	EN 1993-1-8 / EN 1090-2	Design of joints and execution of bolting
International	EN 14399 / ASTM F3125	Preloadable and high-strength structural bolts

Preguntas frecuentes

Do end-plate connections need site welding?

No. All welding of end plates is done in the factory; site work is limited to bolting, which speeds erection and improves consistency.

Must end-plate bolts be pretensioned?

Moment end-plate connections are generally pretensioned. The design drawings state the joint type, and the installer must follow the specified method and inspection.

What causes gaps between end plates?

Mainly weld distortion during fabrication or misaligned members. Plates should be checked for flatness in the shop and gaps limited to the specified tolerance before pretensioning.