Coordinated and Accurate Concrete Detailing with Rebar Constraints in Revit

Concrete Detailing

By Tomasz Fudala

Revit provides tools for Structural Engineers and Detailers for modeling 3D reinforced concrete and generating quantities, shop drawings, and bending schedules in an advanced BIM environment. Revit enables users to design and detail reinforced concrete elements with clash prevention features that improve coordination in the preconstruction and site execution project phases.

Modeling tools in Revit allow Structural Engineers and Detailers to define accurate reinforcement for standard and non-standard shapes of building and infrastructure concrete elements.

In Revit you can use rebar tools to create reinforcement that reacts to changes according to your specified rules—and you can precisely adjust the results.

Shape driven rebars, like the name implies, have their geometry defined from rebar shape families that you can load or create from scratch in the project. These bars expand to fill the concrete host on placement and are automatically constrained to the concrete or to other bars (standard bars to stirrup bars).

Rebar Snapping to Cover

For the concrete element to work as expected (corrosion resistance, etc.), it is very important for bars to respect the concrete cover.

When placing rebar—either directly or by sketching—the bars will automatically snap to the concrete cover or nearby bars. This behavior also applies when adjusting the bars by dragging individual bar handles.

Figure 1: Automatic snapping of the bar to the cover when sketching a rebar.
Figure 2: Automatic snapping of the bar to the cover when dragging an individual bar handle to the element cover.

Shape driven rebars snap intuitively to the concrete cover when you copy or move them (e.g. nudge, mirror, array, etc.). When you move or copy a rebar set, the rebar doesn’t snap to the concrete cover. By not snapping automatically, very small segment length adjustments are eliminated, and the rebar geometry remains consistent. This also prevents new rebar positions (or rebar numbers) from being created. In versions of Revit prior to 2020, a rebar would snap to the cover if closer than half the bar diameter from the cover.

Figure 3: Example – Copying stirrup (A) to produce 3 identical stirrups (B) without the segments snapping to the slightly varying concrete cover.

Rebar Automatic Selection of Constraints

Shape driven rebar segments are automatically constrained only to the concrete host faces that are in the range of each segment (i.e. the segment passes over the face). This ensures that bars do not connect to faces that are far away and subsequently react to changes of those faces. If desired, you can manually select any face (constraint target) parallel to the bar segment, even if it is not within range.

Figure 4: Example – Faces (1), (2), (3) are parallel to the bar segment, while (1) and (3) are also in range of the bar segment; of the two, (1) is closer, so it’s set as the auto constraint

The ends of the bars are automatically constrained to the closest (infinite) surface. The bar ends search for constraints to faces of the host or neighboring elements of the host to which that end belongs.

Figure 5: Stirrup ends automatically constrained to closest (infinite) surface

Standard bars snap to stirrups automatically only if the standard bars pass through the stirrups (i.e. if the stirrups are within range of the standard bars).

Figure 6: Examples – Standard bars snapping to stirrups when passing through the stirrups (i.e. stirrup segments are within range of the standard bar segments)

When a standard and stirrup set are distributed in the same direction (i.e. have parallel bending planes), the standard bar will not snap to the stirrup.

Figure 7: No auto snapping when sets are parallel

Preserve Selected Constraints on Copy

When you manually select a constraint target, that constraint is set as preferred.

If the constrained bar segment is parallel to that face, it will keep that constraint when moving the bar in the same host (even if that face is outside the range of the bar).

Figure 8: Example – Corresponding faces (constraint targets)

When copying the bar from one host to a similar one, the bar will automatically match the selected (preferred) constraints from the source target to the destination host.

Structural hosts are similar if their corresponding faces are parallel and oriented in the same way.

Figure 9: Examples – A varying rebar set with the bar ends manually constrained to face B1 will match that constraint to face B2 when copying to a host with a similar face

Edit Constraints

You can adjust the dimensions of rebar, the distances to concrete elements or other bars, and/or relationships between bars using the Edit Constraints command. Select a bar or a rebar set and click Modify | Structural Rebar > Edit Constraints.

You can change the bar constraint between the cover  or the element face  when the bar segment is constrained to a concrete element.

Control the display of the edited bar in the drawing area via File > Options > Graphics > Rebar Editing.

TIP: Use Space bar to quickly cycle between the visible handles (Shift + Space cycles the opposite way), and Finish editing by pressing Enter. Discard all changes at any time by pressing Esc.

For the selected bar handle, change the distance to its target directly by inputting the offset and confirming using Enter.

This quick navigation between visible handles, as well as direct offset editing is applicable to both shape-driven and free form rebar.

Use the predefined shortcut keys for the specific options (e.g. constraint to face or cover) or add your own key combinations. Click View > Windows > User Interface > Keyboard Shortcuts > Filter and select the Drawing Area Controls category.

Constraints between bars

You can constrain together—at a specified distance—any shape driven rebar sets in the project, regardless of the bar shape or style. This parametric association makes it easier to reuse and adjust rebar patterns throughout the project and ensures that the bars maintain your design intent by reacting correctly to changes of layout, bar sizes and rebar set geometry.

Select a rebar set and Edit Constraints > [select the desired bar handle] > [select a constraint target of one of the bars in the same host as the bar being edited] > [edit the offset and/or other options] > Finish.

Figure 10: The constrained bar will react to changes of the target bar

To select another constraint target, hover the cursor over other bar and valid targets will highlight for selection. These targets can be bar ends, bar segments, the bar plane or out-of-plane extents (i.e. where the set ends).

You can specify constraints between bars in any suitable view (2D or 3D).

Figure 11: Example – (1) current selected handle, (2) constraint target

You can define constraints to bar segments that are perpendicular to the view, e.g. U-shaped bars in a column footing.

Figure 12: Example – Constraining the transverse bars’ bottom segments to the longitudinal bars’ bottom segments in a section view

Clear bar spacing vs distance between bars

When constraining bars together, you can choose whether to specify the clear bar distance or the distance between bar centers when constraining bar segments together.

By default, when constraining a bar segment to another, the bar handle is shifted next to the target segment at a clear distance of 0.

Sign convention

Move the constrained bar segment in the positive direction indicated by the arrow shown on the constraint target by inputting a positive offset (negative moves it the opposite direction).

Overlap bars by constraining the bar start or end to a target bar set’s start or end.

When you constrain a bar end to another bar’s end or to a rebar segment, the end stays in place and doesn’t snap.

A positive offset overlaps the bars, while a negative offset moves the bar ends apart.

You can specify an overlap between (linearly) varying rebarsets as well; the distance between the ends is measured as depicted below.

Two-way constraints

When enabled , a two-way constraint ensures that both handle and target move together when moving or dragging either one. When disabled , only the handle follows the target (not vice-versa).

This option is enabled by default when constraining bar ends together, and it is optional when constraining a bar end, segment or bar plane to another segment or bar plane.

Constraints to any bar or host in the project

You can constrain rebar sets to any bar or concrete host face in the project.

Automatic constraints are set only to faces in the host and “first neighbors” (i.e. concrete elements joined directly to the host) and stirrups in the same host.

Valid constraint targets

Each bar handle is defined by a plane that controls that constraint. Go to a 3D view and edit a bar’s constraints to see a representation of such a plane.

A rebar target is considered valid if the plane of the current bar handle and the plane of the target are parallel. This applies to segments, bar planes (where the set starts and ends) or bars’ start/end.

Figure 13: Example – (1) current selected handle, (2) valid target – parallel segment or concrete face and (3) invalid target (not parallel) – not highlighting when hovering

If a target is not valid, it will not highlight and cannot be selected.

Bars that are already constrained to the current bar (even through other bars) are shown in halftone, and their references cannot be selected, as this would result in a circular reference.

Figure 14: Rebar set (3) is constrained to (2), which is constrained to (1)

In summary, these rebar constraint features help keep designs coordinated by enabling reinforcement to be updated correctly and automatically based on calculated changes. Engineers and detailers can spend less time modelling and documenting reinforced concrete structures—achieving outcomes faster with improved quality and fewer coordination errors.

To learn more, please check the Revit for Concrete Structures YouTube playlist.

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