Why (and When) to Model Rebar in Revit
Modeling rebar for an entire building is very time intensive and takes considerable effort. Modeling rebar for the purpose of meeting an BIM LOD (level of detail) requirement is not recommended, unless that rebar model is going to be pushed downstream into fabrication/construction and used to save schedule or money.
Why/When to Model Rebar
- Shop drawing production
- Why – construction schedule and material tonnage ($$) savings
- Constructability, congestion, and coordination studies
- Why – better constructability, reduced congestion issues, enhanced coordination
Why/When NOT to Model Rebar
- Because you can
- Why not – you’ll blow your budget
- To draw details for construction documents
- Why not – you’ll end up chasing around bar in other unrelated views, modifications are more of a pain, and you can draw details faster using detail components
|FOUR REBAR REVIT MODELS LINKED TOGETHER, COLOR-CODED BY MODEL|
General Considerations for Starting the Model
One of the first things to consider, in the case of a structural engineer acting as EOR for a project and simultaneously creating a rebar model and shop drawings, is whether to combine the rebar and design models, or create two separate models. We prefer to have two separate models, which are obviously then linked and copy/monitored. Here are the pros and cons of the separate model approach:
- Design modeling vs. construction modeling – different needs and LOD
- File size – these models can get very big, and tougher to work with for the design team
- Possibility of design team messing up rebar
- Duplication of work, possibility of design model not matching rebar model
- Some data and details will need to be generated twice
It may make sense to combine the design and rebar model for some firms or for specific projects. In this case, using worksets is a good way to separate the rebar from the rest of the model.
Before starting on a rebar model, we recommend meeting with the fabricator, installer, and GC (or concrete sub) to kick off the project and determine pour breaks, bar lengths, installation preferences, BOM data preferences, etc..
Multiple Rebar Models?
Another thing to consider is whether or not the project justifies the use of multiple rebar models. This may seem counterintuitive from a workflow, model management, and bar numbering stand point. However, the bar numbering problem can be easily solved by using partitions that are created to work across different models.
- Lighter models
- Avoid unintentional interaction between rebar of different element type, like columns and slabs
- If using these models in Navisworks or as linked models, more models to manage
- Need to jump between models to modify different bar in an area where bar from the different models interacts (i.e. core wall dowels and core wall verticals)
Rebar Parameter Management
When setting up and managing parameters in a large Revit rebar model, it is a good idea to take a step back and think about how to best organize these parameters. The goal should be to use the fewest number of parameters possible, and have those parameters be used across a multitude of tools and processes:
- Sheet / view visibilities / filters
- Bend schedules and bills of material (BOM’s)
- Bar marking and numbering
We use the following parameters for the following purposes. We try to minimize the number of parameters to keep the system simple for users, but also flexible across our processes:
|REBAR INSTANCE PARAMETERS|
This is the parameter from which automatic bar numbering in Revit is set. For each partition, Revit will find identical rebar and assign the same rebar number. Therefore, this parameter is extremely important in managing and defining your bar marking and numbering system. Possible uses of the partition parameter are to organize the rebar numbering scheme in your model by construction sequencing and phasing (pours), host element types, location within a host (i.e. top and bottom bar), or location in the model.
Rebar Number Parameter:
The rebar number is defined automatically per partition. This is really the workhorse in automatic bar numbering, and was a very powerful, game- changing addition to rebar in Revit when it was introduced.
|PARTITIONS AND REBAR NUMBERS|
We assign the ‘Pour’ parameter to all CIP elements, parts, and sometimes views. This is used across rebar bend schedules, BOM’s, view filters, and view templates.
As discussed above, this is assigned to rebar and is used in BOM’s, view filters, and delivery QC views.
Bar Comments Parameter:
This is the parameter that we use for a whole slew of view filters, tags, and QC applications. We try to use keywords in the bar comments such as ‘DOWEL’, ‘TOP’ (or ‘T’), E.F., FS, TH, etc. This can be thought of as any extra information that you would like to automatically show up in a live tag, or information that you would like to use to search the model. For example, if you want to find all field bent bar in a model, you can set up a filter for which Bar Comment does not contain ‘FIELD BEND’, and turn that bar off. This is also used for graphic purposes, such as making all bar that has bar comments = (B) turn dashed on slab rebar plans.
User Bar Quantity:
This is assigned to rebar and is used as a work-around. We recommend using this as little as possible. Our main use case for this is for column vertical bar. We typically model column vertical bar as a rebar set on each face of the column, but Revit will only automatically report the rebar quantity for each set. This is how we tell the rebar that is has ’16 - #9 VERT.’, with the 16 being the value that is set in the user bar quantity.
Use of Parameters Across Model Management
The parameters described above are used across the following tools and processes:
Bar Marking and Numbering:
As described above, automatic bar marking and numbering is accomplished by a combination of the Partition and Rebar Number parameters. Our bar marks are simply a combination of the bar size (which is just a type parameter for each rebar size), partition, and rebar number.
|BAR MARKING BY PARAMETERS|
Sheets / Filters / View Templates and Visibilities:
As described above, the Partition and Pour parameters essentially work together to define what type of element the rebar is hosted by, and when this is poured. This is important for view visibilities and view templates, which are controlled extensively by filters. For example, you usually don’t want your rebar shops to show concrete elements that will not be formed at the time of rebar placement. For something like slab rebar shops, you probably won’t want to see column rebar, so you can easily use a filter to turn off the partition that contains all column rebar.
Bend Schedules and BOM’s:
BOM’s are filtered down to only a specific ‘Delivery’ data input, but bend schedules use a combination of parameters to filter the bar data down to only what we want to see on a specific sheet. We use Partition, Pour, and Grade to filter down our bend schedules to only show the rebar that appears on specific sheets.
We have found it best to keep our tagging scheme as simple as possible, and not let users create new tags for any new use case they come across. Our tags only contain bar quantity, ‘type name’ (bar size), bar length (for straight bar) or bar mark for bent bar, spacing, and bar comments. We do have different tags for where the ‘break’ is shown in the tag, and for bent bar vs. straight bar.
|REBAR TAG OPTIONS|
QC Views and QC Schedules:
The use of the parameters described above in QC view and QC schedules is endless. We use a variety of filters to isolate only certain properties of bar (such as its placement in a slab, its size, grade, etc.), and then often assign color to those filters to make the QC process of a model with tens of thousands of pieces or rebar much more manageable.
REVIT REBAR MODELING OUTSOURCING SERVICE
Our Revit rebar detailers are skilled in developing detailed drafts for rebar installation detailing, and are familiar with construction practices to address the constructability issues that may arise on site.
Our rebar detailing services include:
- 2D and 3D Modelling of Rebar
- Rebar detailing, drawing, estimating, and 3d modeling
- Quality take-offs & As-built drawings
- Bar bending schedules
- Foundation drawings
Please contact us and let discuss about your project.