The bolted end plate joint at the eaves of a portal frame to EN 1993-1-8: why it is haunched, its bolt rows, the compression zone, the column web panel, stiffeners, welds, and the reversed moment under uplift, with the STATIX haunch calculator.
1. Learning outcomes
After this lesson you can:
say why the eaves is haunched and what the haunch does to the joint;
read a row-by-row end plate check (6.2.6, 6.2.7);
check the compression zone and the column web panel;
decide when the column needs stiffeners, and check the welds;
The same lesson in the SA course: Steel Design 2, lesson 5 (the same EN method, with SANS cross-checks).
3. The joint
Why a haunch. At the eaves the moment is the largest in the frame. A haunch deepens the rafter there, so the bolt rows sit much further from the centre of compression at the haunch flange: the same bolts give a much larger moment resistance, and the plain rafter beyond the haunch can stay light.The parts. The column, the rafter, a haunch usually cut from the same section, an extended end plate welded to rafter and haunch, tension bolt rows near the top, and a row near the bottom. The STATIX haunch calculator lays the rows out itself from the number of rows, the pitch and the haunch depth.What the haunch calculator uses. Its method is the component method of EN 1993-1-8 6.2 alone (its code picker is fixed), with the recommended partial factors, the fu of the plate and the members by thickness from EN 1993-1-1 Table 3.1, the column as it is (unstiffened) and the axial force kept in the force balance.
4. Tension rows
Bolt rows as T-stubs (EN 1993-1-8 6.2.4; Steel Design 1 lessons 5 and 6). The end plate and the column flange each act as a T-stub round every bolt row: the plate yields, plate and bolts fail together, or the bolts break. Rows close together can also fail as a group.Row by row. The calculator takes each row’s resistance (plate, column flange, column web in tension, bolts) and the groups of rows, then checks the row forces of a linear distribution about the compression centre, and sums the moment resistance Mj,Rd (6.2.7).
5. Compression, panel and stiffeners
The compression zone. The tension in the rows is balanced at the haunch flange, which pushes on the column web opposite it. The column web may crush or buckle (6.2.6.2), and the haunch flange and web must carry the force (6.2.6.7); the smaller sets the compression limit.Column web panel shear. The pull at the top and the push at the bottom of the joint shear the column web panel between them. In a one-sided joint like an eaves the whole joint force goes into the panel (β = 1).Stiffeners. Where the column flange, the web in tension or compression, or the web panel is too weak, stiffen the column: plates level with the rafter flange and the haunch flange, a supplementary web plate or a diagonal. The STATIX page checks the column as it is, unstiffened; if a column row fails, stiffen (the showcase frame’s interior eaves has column stiffeners) or choose a heavier column.
6. Welds, the haunch and reversal
Welds. The rafter flange welds carry the flange force; the web weld is designed full strength (Steel Design 1 (Eurocode) lesson 6); the haunch is welded to the rafter and its web to its flange, each checked for the shear flow. The page checks them with the EN directional method.Haunch rules. EN 1993-1-8 6.2.6.7(2) lets the haunch count in the joint when its steel matches the rafter and its flange is no steeper than 45°. At the toe the haunch flange force turns into the rafter web, checked by EN 1993-1-5; the plain rafter there is lesson 3’s haunch-tip section.Moment reversal. Under uplift (lesson 3) the eaves moment changes sign: the bottom row goes into tension and the rafter top flange pushes on the column. The STATIX haunch page takes M as + for gravity and − for uplift, and checks a negative (reversed) moment on the mirrored joint: the bottom row and its T-stub in tension, the rafter top flange and the column web opposite it in compression, and Mj,Rd of the reversed sense.
7. Example A: the eaves under gravity
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8. Example B: the eaves under uplift
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9. Do it in STATIX
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10. Common mistakes
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11. Exercises
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12. Self-check quiz
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13. Lesson 4 on one page
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Next: Lesson 5, the apex connection and the baseThe apex under both signs of moment, and the pinned base with its anchors under compression and uplift. Go to lesson 5
A worked example for learning, not a design. Check every value against the current code, your national annex and your own project, and have the design checked and signed by a registered professional engineer.
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