The last two joints of the portal frame: the bolted apex under gravity and uplift to EN 1993-1-8, and the pinned column base with its anchors to EN 1993-1-8 and EN 1992-4, under compression and under uplift, with the STATIX apex haunch and base plate calculators.
1. Learning outcomes
After this lesson you can:
check an apex joint for both signs of moment;
apply the haunch rules at the apex;
check a pinned base under compression and under uplift;
check holding-down anchors in tension (EN 1992-4) and the shear transfer;
The apex. The two rafters meet at the ridge, each with an end plate; the plates are bolted to each other, usually with a short haunch below to deepen the joint. There is no column: both sides of the joint are plates.The sign at the apex. Under gravity the apex sags: the bolts near the haunch flange are in tension and the rafter top flange is in compression. Under uplift it hogs and the top bolts take the tension. Both cases need checking.The ridge bolt layout. The STATIX apex page lays the rows out in two clusters, half near the rafter top flange and half near the haunch flange, so one cluster is in tension whichever way the moment turns.What the apex page checks. It runs the EN 1993-1-8 component method on the haunched ridge with the moment’s sign kept, so the gravity case (tension in the cluster near the haunch flange) and the uplift case (tension near the rafter top) are each checked as they are.The apex haunch follows the eaves haunch rules of lesson 4: the same steel as the rafter, a flange no steeper than 45°, welds checked for the shear flow, and the toe where the flange force turns into the rafter web.
4. The pinned base
The pinned portal base. Most portal columns stand on a plate with four anchors near the column and a grout layer, treated as a pin: it passes axial force and shear but no moment, which keeps the footing small (Foundations 1) and the frame moments as lesson 3 found them.Actions at a pinned base. Under gravity the column pushes down with a horizontal thrust outward; under uplift the column pulls the base up, and the wind adds to the horizontal force. The holding-down bolts and the shear transfer both need the uplift case.Holding-down bolts in tension. The plate bends round the anchors (a T-stub, as in Steel Design 1 (Eurocode) lesson 7); each anchor needs its steel strength and its anchorage in the concrete: cone breakout and pull-out of the head. The STATIX page checks the anchorage by EN 1992-4, with the anchor steel on its stressed area As.Shear transfer. Friction under the plate works only while the base is in compression (0.20 Nc,Ed for sand-cement mortar, EN 1993-1-8 6.2.2(6)). Under uplift the anchors carry the shear, and anchors that are also in tension count at only 0.4/1.4 of their shear resistance (6.2.2(2) NOTE), or a shear lug under the plate does, with its own concrete and geometry rules.Anchor position. This lesson’s base has its anchors outside the column flanges. Many pinned bases put them inside the flanges, close to the web, to keep the joint flexible; the base plate page takes that layout as a pinned base too.
What the two pages use: the apex page runs EN 1993-1-8 6.2 with the moment’s sign kept and the plate’s fu by thickness; the base plate page, on its “EN 1993-1-8 + EN 1992-4” route, takes fck as the cylinder strength, βj 2/3, kj 1.0 with no pedestal declared, friction 0.20 Nc,Ed, Fvb,Rd by 6.2.2(7), the 0.4/1.4 rule for anchors also in tension, and the anchors by EN 1992-4 with the steel on As.
5. The course
The course on one building: from layout and load paths, through the cold-formed purlins and girts, the frame members and the eaves, to the apex and the base that takes it all into the footing.
6. Example A: the apex, both ways
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7. Example B: the pinned base
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8. Do it in STATIX
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9. Common mistakes
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10. Exercises
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11. Self-check quiz
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12. Lesson 5 on one page
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Course completeYou have finished Steel Design 2 (Eurocode): one portal frame building from layout to the base. Go back to the course page, or compare any lesson with its SANS twin. Back to the courseSteel Design 2 (SANS)
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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