How a beam cage and a column are put together: main and top bars, curtailment, link zones, closed and open links, cranks, side bars and the joint at a column; then column starters, laps, link arrangements, a change of section and the top of the column.
1. Learning outcomes
After this lesson you can:
lay out a beam cage and curtail bars the way the RC beam calculator’s detailing checks them;
set link zones and choose closed or open links;
add side bars to deep beams and detail the joint at a column;
arrange column bars and links, and detail starters, laps and the top of a column;
A beam cage: main bottom bars, top bars over the supports, hangers to carry the links in the span, and links along the whole beam (4.11.4.5.3), closer where the shear is high. Deep beams add side bars.Curtailment as the RC beam calculator checks it. A bar can stop where the bars that carry on can take the moment (the dotted MR line), but it runs on past that point by at least the effective depth or 12 bar sizes, and either its anchorage length or to where the bars that carry on give twice the area needed.Top bars at an interior support and a cantilever. The top steel over the support must run past the point of contraflexure in the next span and on by max(d, 12φ) where it is no longer needed (4.11.7.1.4 with 4.11.7.1.1). Never stop cantilever top bars at the support face.
4. Links
Link zones. Shear is highest near the supports, so the links are closer there and spaced out towards mid-span. Every zone keeps the limits: spacing along the beam at most 0.75d, legs across it at most 0.75d apart, and the minimum links of 4.11.4.5.3 everywhere. Change spacing in a few clear steps.Closed or open links. A closed link (shape 60, 135° hooks into the core) is needed where the beam carries torsion and where compression steel must be restrained. An open U-link with a closing bar is easier to fix under a slab, but only where neither applies. Each corner of a link must pass round a bar at least its own size (4.11.6.4).
5. Cranks, side bars and the joint
Cranks. Bars are cranked to change level: a bottom bar rising to the top over a support (shape 41), or a bar stepping at a change of beam depth (shape 038). Two bends turned opposite ways out of the plane is not a 38: STATIX schedules it as 99 with a sketch.Side bars on deep beams (4.11.4.4). In a beam deeper than 750 mm, bars along the side faces control cracks over two-thirds of the depth from the tension face: at most 250 mm apart, and each at least √(sb b/fy) in size, with b taken as no more than 500 mm.The support detail at an edge column. Beam bars that end in a column need their anchorage there (4.11.6.3), counted round the bend (4.11.6.8.2) with the bearing check inside it. The bends turn into the joint, inside the column bars, and the legs must fit the concrete; a bend turned out of the concrete earns nothing.
6. Columns
Column link arrangements. Every corner bar and at least every other bar along a face sits in the corner of a link or cross-tie, and no unheld bar is more than 150 mm from a held one; the column calculator checks it. With more bars per face, add cross-ties or a second link.A change of section. Where the column above is smaller, the bars below cannot run straight into it: crank them inside the floor zone or stop them and add starters. STATIX checks that every outer bar stays inside the column above over the lap and flags it when not. Links: at least a quarter of the largest bar, at no more than 12 times the smallest (4.11.4.5.1).The top of the column. With nothing above, the bars run to the top of the roof beam or slab less cover. Where that straight length is less than the tension anchorage, STATIX bends a leg into the beam (shape 37), at least 12φ and as long as the anchorage still needs, rounded up to 25 mm.
Starters and the lap above the floor follow lesson 3: a compression lap where the column stays in compression, the tension lap where it can pull.
7. Example A: beam B2
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8. Example B: column C1
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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, slabs, footings and wallsSlab mats, openings, corners, footings, pile caps and walls. Go to lesson 5
A worked example for learning, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.
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