Tutorial 36: Reinforcement & Panel Dowels

Everything so far has been something cast into the panel or cut out of it. This lesson is about the steel — the mat that makes a slab of concrete into a panel that can be picked up, and the dowels along its base. One of those you can place today, and it is a bigger thing than its name suggests: the row labelled Slab Dowels is the panel’s permanent connection to the ground.

Feature

What it is

Standard

In ConstructiVision

Slab dowel

The J-shaped bar that completes the panel’s permanent base connection

ACI 318 · ACI 551.2R

built today — the Slab Dowels row, six of them

Panel-to-footing tie

The base connection itself, made by bar or by cast-in plate

ACI 318 §16.3

built today — the same dowel row, or a base embed below finished floor

Welded-wire mat

A factory-welded wire grid used as distributed reinforcement, and its cover

ASTM A1064 · ACI 318

not modeled

Post-installed / epoxy dowel

A dowel drilled and bonded after the concrete has cured

TCA Detail Library

partly — nameable as its own embed type; the drilled-in values are not modeled

There is one dowel feature, not two — and it is the base connection

It is easy to read “slab dowel” as a minor slab-edge detail and go looking for a separate panel dowel that ties the wall to its footing. There is no such second control, and there does not need to be one: the Slab Dowels row is the panel’s permanent base connection. It is the steel crossing the panel-to-foundation joint, it is what resists the panel sliding at its base, and it is what lets the temporary braces come off. Step 3 is a follow-along you can run in your own panel.

The welded-wire mat is genuinely not modeled — Step 2 is marked (planned). The post-installed dowel is half expressible today, and Step 5 says exactly which half.

Note

A browser version covers part of this lesson. Open it here — it lists exactly which steps it does not cover, so you know what to come back to AutoCAD for.

What you will learn

  • Why the reinforcing mat is on the panel drawing at all, when the engineer specifies it.

  • The two values that define a welded-wire mat, which one goes wrong, and why it has nowhere to go in the product today.

  • That the Slab Dowels row is the base connection rather than a slab-edge detail — and what that changes about the numbers you type into it.

  • What the dowel row records, and the three things it does not carry that still have to reach the yard.

  • How the base connection gets to the crew placing embeds in the footing.

  • What makes a dowel post-installed, why that moves responsibility to the field, and how to say so on the drawing today.

Before you start

Watch the lesson

Warning

What this recording does and does not demonstrate. It places the slab-dowel row of Step 3 on TP08-12 at Elevation −3”, Max Spacing 1’-6”, Length 2’-0” and Inset 9”, and zooms in on the redrawn row so its note and elevation marker can be read. The welded-wire mat (Step 2) and the post-installed epoxy dowel (Step 5) are described, not placed: they are not in the product yet.

Lesson

Step 1 — Why reinforcement is on your drawing

The reinforcing design is the engineer’s. So why does the panel book carry it?

Because a tilt-up panel is the one structural element that gets picked up. A wall poured in place never sees a load until the building is on it. A tilt-up panel is lifted flat off the ground, rotated through ninety degrees, and set — and during that lift it is loaded in ways it will never see again. The panel that survives the lift and the wall that stands afterwards are the same object judged against two different load cases.

So the mat has to be on the drawing the crew works from, at the panel it belongs to, because the panel is fabricated in the yard by people holding that drawing. There is no second chance: once the concrete is placed, everything in this lesson is either in the panel or permanently absent from it.

Tip

One nuance worth carrying into the yard: the lift stress itself is checked on the uncracked section, without crediting the mat. Adding mat steel does not reduce what the panel feels during the pick — concrete strength at lift and where the pick points go are what do that (Tutorial 9: Brace Points & Expansion Gaps). The mat is there for the finished wall and for crack control.

Step 2 — Welded-wire mat (planned)

A welded-wire mat is a factory-welded grid of cold-drawn wire, laid in the bed before the pour and held at a set distance from the casting surface by chairs.

Two values define one, and one of them is the value that goes wrong:

  • the mat designation — the wire spacing and wire size, from the engineer, written like 6×6 W2.9×W2.9;

  • the cover — how far the mat sits from the face.

Cover is the one that gets missed. A mat sitting on the bed instead of up on chairs is a mat doing nothing where it is needed, and it is invisible the moment concrete goes in. On a lay-flat casting bed the chairs set the cast-down-face cover, which means the value is decided by a decision made on the ground minutes before the pour, by whoever is placing the steel.

Intended behaviour: a reinforcement entry taking the mat designation, cover, and extent, reported in the materials list by area — mats are bought by the sheet or the roll, and an area converts to both. Where the mat is interrupted by an opening, the extent follows the opening, because that is what actually gets placed.

What you can do in the meantime, and what you cannot. The project embed catalog (Add weld connections → Edit Embeds) will hold anything you can describe as a Type with a width, a height and a thickness, and its Type mark is printed on the drawing and carried into the materials list. That is enough to record that a mat is called for, and it is better than leaving it off.

It is not the feature, and the gap is precisely the value Step 2 is about:

  • A mat is a plane of steel, not a solid block. The catalog describes boxes.

  • Cover has no field. Nothing in the embed record says how far off the casting face the steel sits, and cover is the whole point of this step.

  • The materials list totals embeds by type and count. Mats are bought by area, so a count is not a quantity anyone can order against.

Until the mat is a feature, write the designation and the cover on the drawing as a note and treat the catalog entry as a reminder, not a record.

Recorded, not certified

ConstructiVision records the values you enter and carries them to the drawing and the materials list. It does not design reinforcement, calculate lifting stresses, or check that a mat is adequate for the pick. Those are the engineer’s, and the panel book exists to carry their decision to the yard without it changing on the way.

Step 3 — The dowel row is the base connection

Here is the sentence to keep: a slab dowel is not a tidy-up detail between the panel and the floor. It is what holds the wall down.

Slab dowels are J-shaped lengths of rebar embedded in the panel wall that protrude from below finished floor and extend into the slab, anchoring the panel to the slab and to other floors after the closure strip is poured. Their structural job is two things, and the second one is why this step exists:

  1. They transfer in-plane shear from the panel into the floor diaphragm.

  2. They resist the panel sliding at its base under wind or seismic load. The steel crossing that joint is what makes the friction across it work at all — remove the dowels and the mechanism goes with them.

That second job is the panel’s base load path into the ground, which is why the row is a structural connection rather than an edge detail, and why it is the thing that lets the crew take the temporary pipe braces off (Tutorial 9: Brace Points & Expansion Gaps). Before the dowels are in and the closure strip is poured, the braces are the only thing holding the panel.

The vocabulary trap

“Panel dowel”, “base dowel” and “slab dowel” all name the same steel in the field, and it is easy to conclude from the name Slab Dowels that the panel-to-foundation tie must live somewhere else. It does not. Searching for the industry’s word for a thing is the fastest way to decide, wrongly, that a feature is missing — the same trap Tutorial 38: Corbels, Haunches & Spandrel Seats describes for corbels.

To place a row: click Slab Dowels on the toolbar, or check Slab Dowels in the Main Panel Details feature checklist (Tutorial 2: Panel Options) — either route opens the same dialog. There are six rows. On a free row:

  • Enable — as in every feature dialog, an unchecked row keeps its values and stays out of the drawing.

  • Elevation — from finished floor to the centre of the row. A value below the panel bottom or above the panel top raises a warning.

  • Maximum Spacing — the maximum spacing between dowels. Under 6” or over half the panel width raises a warning, and the actual spacing may be tightened when the panel is drawn so the inset you asked for is kept.

  • Length — “the length that the Slab Dowels extend from the near face of the Panel (into the closure strip)”. This is the projection past the panel face, not the bar’s total length. A negative value raises a warning.

  • Inset — the absolute inset of the first and last dowel from the sides of the panel, or of the row segment. It may be adjusted to centre the array, unless that would conflict with the rule of at least one dowel per row segment.

  • If Dowels intersect openings, they should: — Trim removes the dowels from the intersecting opening entirely; Offset places them around and underneath it; Extend from Top and Extend from Bottom carry them from the opening edge and stub them out at the row elevation.

Confirm with OK. Check the drawing: the length, spacing and inset are written as text along the dowel row, and an elevation marker dimensions the centre of the row. That text is what the yard reads.

What the row handles for you

Worth knowing before you go looking for a bug, because none of this is obvious from the dialog:

  • A row that crosses every opening is segmented and moved down 3” below the opening, and each segment keeps at least one dowel.

  • If there is less than 3” between the bottom of the opening and the bottom of the panel, the segment snaps tight to the frame; under 1”, the dowels in that opening are dropped.

  • A dock leveler gets additional dowels along the vertical sides of its leveler pit, so the panel ties to the pit walls (Tutorial 39: Dock Details — Leveler Pits & Door Guards).

  • The specified spacing and inset are held for each segment independently.

What the row does not carry

Three things the dowel row does not state, all of which still have to reach the yard:

  • No bar size or grade. The dialog gives elevation, spacing, length and inset. The bar size, grade, lap and development come from the structural general notes and the base-connection detail — so a panel drawing showing dowels still needs its detail reference beside them.

  • No embedment on the far side. Length is what projects past the near face. What the bar does inside the panel is not a field here.

  • No line in the materials list. The list totals concrete, form material, anchor bolts, chamfer, feature strips, pick points, brace points, braces, extensions and embeds (Generate a materials list). Dowels are drawn, dimensioned and annotated — they are not a quantity line, so the bar tonnage is counted somewhere else.

One thing to check by eye

The geometry around openings is handled, but you are not warned about it. With Trim selected, a dowel that crosses an opening is simply removed — quietly, with nothing on the drawing saying a length of base connection went missing. A dock leveler pit is the case that catches people, because the pit notches the panel exactly at the base, where the dowels live, and the pit is entered on a different dialog from the dowels.

Look at the panel base after placing a dock or a low opening, and confirm the run that remains is the run the base detail asked for.

Step 4 — Getting the base connection to the footing crew

The bar is one way to make the base connection. The other is a cast-in plate at the panel base, mating to a plate or bolts set in the footing — the connection-to-foundation case in ACI 318 §16.3.

ConstructiVision places that one as an ordinary weld connection at an elevation below finished floor (Tutorial 7: Weld Connections). There is real panel down there to put it in: panel bottoms routinely sit below finished floor — the sample panel’s is 1’-6” below it (Tutorial 2: Panel Options) — and any type in the project embed catalog can be placed at a negative elevation like any other.

What makes a base embed different from every other connection in the panel book is that it has a mate in somebody else’s concrete. A roof-joist plate only has to be right relative to the panel. A base embed has to line up with an embed the footing crew set weeks earlier, and neither crew can fix it afterwards.

That coordination is what the site drawing’s Footing Connection Layout is for: it finds every embed below finished floor across the attached set, dimensions each one from the grid lines and from its neighbours, and produces a plan slice showing only the panel outlines and the footing connections — a sheet you print, in the manual’s words, “to assist your embed placement crew in aligning the embeds in the footing with the embeds in the Panels.”

That layout is not in this release. The panel-side placement works today; the site-side collection does not — Footing Connection reports that it is not available, alongside the Footings, Column Pads and Weld Connections site buttons that are present but disabled (Lay out the site). Until it arrives, do the coordination by hand: dimension the base embeds from the grid on the site drawing yourself (Tutorial 10: Site Drawing), or issue the panel elevations to the footing crew with the base connections marked. Skipping it is the expensive option — a base embed in the wrong place is discovered by a crane holding a panel.

Step 5 — Post-installed epoxy dowel (partly planned)

A post-installed dowel is drilled and bonded with adhesive after the concrete has cured, rather than cast in. It is what gets used when a cast-in dowel was missed, when a connection is added later, or when the sequence makes casting impractical.

Two things change, and the second matters more than the first:

  1. It has a different capacity, from the adhesive manufacturer rather than from the concrete design — so it is specified by an adhesive system and a hole diameter and depth, not just a bar size.

  2. It moves the responsibility. A cast-in dowel is the precaster’s. A post-installed dowel is installed on site, in conditions nobody controlled, and its capacity depends on the hole being clean and the adhesive being placed correctly. It is an inspection item in a way a cast-in dowel is not.

Half of that is expressible today — the half that matters most. The point of the second item is that the drawing has to say which one this is, and saying it is exactly what the embed catalog is for. In Edit Embeds (Add weld connections), the Type mark you give a connection “will be the identifying text printed on the final drawing and included in the Materials List function”, and the Description, Structural ID and Fabricator ID fields ride along into the list for cross-reference. So:

  • define a type whose Type mark names it as post-installed, and put the adhesive system and the hole in its Description;

  • place it at the position it belongs;

  • the drawing carries the callout, and the materials list segregates it by type — which is the separation a field-installed item needs.

That is the same pattern the shear connector wants in Tutorial 35: The Insert Family: same geometry, different callout, and the callout is the point.

The limits, honestly. A dowel is a bar, and the catalog describes a width, a height and a thickness — a solid box. An embed is placed to a point and reported as a count. And nothing anywhere carries a field-installed flag, so these do not sort themselves out of the precast quantities; you do that when you read the list. Treat it as a stopgap, the same way Tutorial 33: Bearing Seats & Embedded Angles treats a long thin embed standing in for an embedded angle.

Intended behaviour, for the part that is missing: a cast-in / post-installed flag on the dowel row itself that changes what is required — post-installed adding hole diameter, embedment depth and adhesive system — and marking the item as field-installed on the drawing and in the schedule, so it appears where field work is tracked rather than in the precast quantities.

Tip

If a set of panels shows many post-installed dowels, that is worth a second look at the panel book rather than a shrug. It usually means cast-in dowels were being missed, and the fix is upstream.

Recorded, not certified

ConstructiVision records the dowel elevation, spacing, length and inset you enter, and the embed types you define, and carries them to the drawing and the schedules. It does not size dowels, calculate sliding resistance, check development length or cover, or verify an adhesive system’s capacity. Those are the engineer’s, and the base connection is one of the places where that line matters most — it is the load path out of the building.

Check your result

You should now be able to:

  • Say why a tilt-up panel’s reinforcement belongs on the fabrication drawing even though the engineer designs it, and why the mat does not reduce what the panel feels during the pick.

  • Name the two values that define a welded-wire mat, say which one gets missed, and say why the embed catalog cannot stand in for it.

  • Explain why the Slab Dowels row is the panel’s base connection rather than a slab-edge detail, in terms of the two structural jobs it does.

  • Place a dowel row, and say what Length is measured from and to.

  • Name the three things the dowel row does not carry, and where each of them comes from instead.

  • Say what happens to a dowel run that crosses an opening under each of the four options, and which one removes base connection without telling you.

  • Say why a base embed is different from every other connection in the panel book, and what you have to do by hand in this release because of it.

  • Explain the two things that change when a dowel is post-installed, say which one is about people rather than capacity, and record that one on the drawing today.

Where next