Tutorial 38: Corbels, Haunches & Spandrel Seats

Three ways of making a panel thicker in one place so something can land on it. They look alike in section, they are built the same way, and the standards keep them apart — because what they carry, and where the load goes afterwards, is different in each case.

Feature

What it is

Standard

In ConstructiVision

Corbel

A horizontal bracket projection

ACI 551.2R

the Lintel

Haunch

The thickened section where a pilaster or lintel extends from an edge to support a joist or beam

TCA

a pilaster or lintel extended past the panel edge

Spandrel seat

A seat for a spandrel panel or member

Field practice

a Recess/Blockout or Standard Opening snapped to an edge

All three are placeable today — and only one is called what the catalog calls it

What this lesson mostly teaches is vocabulary, because the single most likely way to conclude ConstructiVision cannot do something is to search for the industry’s word for it.

ConstructiVision calls a corbel a Lintel. The user manual says so directly — “A Lintel (Corbel) is…” — and everything corbel-shaped is placed through Pilaster / Lintel Details. The haunch has no control of its own by design, and Step 2 explains why that is the right design rather than a gap.

The spandrel seat has no tile of its own — ss_dlg ships with no entry point (CV-2036) — but it is not missing: the manual names it as something you make with a Recess/Blockout or a Standard Opening snapped to an edge. Step 3 shows that route.

Note

This lesson also exists in the browser. Work it in ConstructiVision on the web — same steps, same values, so you can follow either and end up with the same panel.

What you will learn

  • That the control you want for a corbel is called Lintel — and why searching for the industry’s word is the fastest way to conclude, wrongly, that a feature is missing.

  • Why ACI treats a corbel as a distinct element from a lintel, when both are horizontal projections.

  • How to make a haunch without a haunch control, and why there deliberately isn’t one.

  • Where a spandrel seat fits, and how it relates to the pilaster and lintel you already know.

Before you start

Watch the lesson

Warning

What this recording does and does not demonstrate. On TP08-12 it places two rows in Pilaster / Lintel Details. Row 1 is a corbel, entered as a Lintel: Snap To B cleared, 10’-0” from the left, elevation 13’-0”, 2’-0” wide, 1’-0” high, 8” Add’l Thk. Row 2 is a pilaster snapped to the bottom, 2’-6” wide and 16’-0” high, with a Distance of −1’-0” meant to carry it past the edge as a haunch. On this build that Distance is greyed out by Snap To B, so the pilaster draws at the edge and the haunch does not appear (see the warning in Step 2). The spandrel seat (Step 3) is described, not placed.

Lesson

Step 1 — Corbel versus lintel

In the standards these are two elements. In ConstructiVision they are one control, and knowing why tells you what to enter.

Both project horizontally from the panel. The difference is what is above them:

Lintel

Corbel

Spans

across an opening

nothing — it is a bracket

Supported at

both ends

one end only, by the panel

Carries

what is above the opening

whatever lands on it

Governed by

flexure across the span

shear friction at the panel face

That last row is why ACI 551.2R treats a corbel as its own element. A lintel is a beam and behaves like one. A corbel is a cantilever with a very short shear span, and it fails at the interface with the panel rather than in the middle. It is reinforced differently for that reason.

For our purposes the consequence is dimensional: a corbel’s projection and its bearing width are the values that matter, and the bearing point’s distance from the panel face is the number the engineer designed around.

To place one: open Pilaster / Lintel Details and enable a row. The columns are Distance, Elev Left, Elev Right, Width, Height, Add’l Thk and U/D.

  • Add’l Thk is the projection — how much thickness the element adds to the panel. That is the value that makes it a bracket rather than a line.

  • Elev Left and Elev Right are separate, exactly as on the feature strip (Tutorial 29: Feature Strips & Reveals), so the top can step or slope.

  • U/D decides which face it projects from.

There are 24 rows across four pages, and a Calc button for working the values out.

Step 2 — Haunch

A haunch is what you get when a pilaster or a lintel does not stop where the panel does — it extends out from the edge, thickening the section, to carry a joist or a beam.

There is no haunch control, and that is the right design rather than a gap. A haunch is always the extension of something else; placing one on its own would describe a lump of concrete with nothing behind it. So you make a haunch by making a pilaster or lintel that runs past the panel edge.

Take a pilaster row and give it a Distance and Width that carry it beyond the edge. The section thickens out past the panel and you have a haunch. The user manual puts it plainly: “Pilasters or Lintels may also be extended from either edge of the Panel to produce supporting haunches for roof joists.”

Warning

On the current build a bottom-snapped haunch draws at the panel edge. Ticking Snap To B also greys out Distance (the manual says it disables only the elevations), so a negative Distance on a pilaster row is ignored and the pilaster starts at the edge rather than past it. The video shows this. Until it is fixed, check the redrawn panel: a haunch that does not reach past the edge has not been drawn.

Tip

Because the haunch is its pilaster rather than a second object beside it, moving the pilaster moves the haunch — automatically, with no chance of the two disagreeing. Worth noticing: the usual failure, where a haunch stays put after its pilaster is revised, cannot happen here.

Step 3 — Spandrel seat

A spandrel is a panel that spans horizontally between supports — above an opening, or as a band across a facade — rather than standing from the floor. A spandrel seat is what it lands on.

You place one with a Recess/Blockout or a Standard Opening, snapped to an edge. The user manual names it directly in both places — “…Throughs, and Spandrel Seats. A Recess or Blockout can be snapped to either Left or Right and/or Top or Bottom” — and the same sentence appears for Standard Openings. Snapping to an edge is what forms the seat.

There is no tile literally labelled Spandrel Seat — the ss_dlg dialog ships in the build with no entry point (CV-2036) — but the capability is not missing, only the shortcut. Give the blockout the bearing width you need and snap it to the side the spandrel lands on.

A spandrel can also sit on a corbel or a haunch from the steps above, or on a steel seat angle from Tutorial 33: Bearing Seats & Embedded Angles. Which one gets used is an economics and detailing decision, and the drawing has to say which was chosen, because they are built by different trades.

Step 4 — Reading them apart in section

All three appear in section as the panel getting thicker. Tell them apart by asking two questions:

  1. Does it continue below? If yes, it is a pilaster or a haunch on one. If no, it is a corbel or a seat.

  2. Is something spanning across it, or landing on it? Spanning means lintel. Landing means corbel, haunch or seat.

A drawing that does not let a reader answer those two questions has not communicated the detail, whatever the dimensions say.

Recorded, not certified

ConstructiVision records the projection, bearing width and elevation you enter and carries them to the drawing and the schedules. It does not calculate shear friction, size the corbel reinforcement, or check the bearing. Those are the engineer’s, and a corbel is one of the places where that distinction matters most — the reinforcement detail is what makes a corbel work, and it comes from the structural drawings.

Check your result

You should now be able to:

  • Say which ConstructiVision control places a corbel, and why it is not named “corbel”.

  • State why a corbel is a distinct element from a lintel, in terms of how each is supported and how each fails.

  • Place a corbel through Pilaster / Lintel Details and say which column is its projection.

  • Make a haunch by extending a pilaster past the panel edge, and say why there is no haunch control.

  • Place a spandrel seat, and name the three ways the same load could have been carried instead.

  • Tell the three apart in a section drawing using the two questions in Step 4.

Where next