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  • Structures in Revit

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    Structures in Revit


    One of the promises of BIM (Building Information Modeling) technology like Revit Structure for project design is that much of the busywork of creating construction documents will be reduced so that you can concentrate on the design of the project rather than wrestling with the design software. The use of model elements is a good case in point.

    Two distinct types of model elements exist in Revit Structure:

    • Host elements are generally system families that represent real-world construction elements such as walls, slabs, roofs, and stairs. These elements, as their name implies, often host other elements, such as openings in a wall or reinforcement in a slab.
    • Component elements are used to represent all other real-world construction elements, including beams, trusses, columns, and reinforcing bars. These elements are typically external families that are loaded from the Revit Structure libraries into the project as needed, similar to their real-world counterparts being trucked or shipped to the site for assembly.

    How Much Should I Model?

    How much should you model, and how much should you just add in 2D?

    You need to ask yourself this question quite often as you proceed with modeling your project. You might model the columns but not model the base plate and bolts in your project if you work for a design engineering firm. In that case, modeling a few typical cases of various connection types will be sufficient.

    On the other hand, if you work for a detailing or construction management firm, you might have to model every piece in the structure. The scope and extent of your model-building are relative to the documents that will be derived from it as well as the BIM solution you are trying to achieve.

    The bottom line to knowing how much to model in your project is that you must maintain the essential integrity of the model by creating and maintaining the necessary elements to suit your purposes.

    Most of your modeling will use these elements, so it is important for you to understand their basic properties.

    Datum Elements

    Grids, levels, and reference planes are datum elements. These elements provide the framework in which the building elements are placed and flexed. As you add your model elements to the project, they will become fixed to the datum elements. These basic modeling constraints then become anchors for objects, so that if you need to change a bay width or the story-to-story height of a level, those elements will also move correspondingly.

    For example, beam elements placed in a third-floor plan view are associated with that datum. Changing the elevation of the level will take the beams along for the ride because they are defined as belonging to that level. This makes floor-to-floor clear height adjustments quick and accurate.

    Datum elements also behave in a special way when it comes to the documentation of your project: they automatically appear in all relevant views. As such, datum elements are an essential part of a constraint-based modeling system and are fundamental to how you will assemble and edit the design.

    View-Specific Elements

    View-specific elements are used to annotate and detail specific views of the model for the creation of your construction documents:

    • Annotation elements include text notes, tags, keynotes, dimensions, spot elevations, spot coordinates, and symbols. These elements play a critical role in translating the model into construction documents. Unlike simple annotations found in other platforms, the majority of the annotation elements in Revit Structure have a great deal of intelligence. Tags, for example, are annotations that display specific parameter values contained in the model elements. Change the size of a beam in the model, and all tags that you have already placed will be updated automatically. Adding text is also a view-specific element.
    • Detail elements pick up where the model elements leave off. Some items are not worth the time, effort, or performance overhead to model and can easily be handled with the addition of simple 2D line work or by adding 2D detail components, such as to a section cut through the model. These elements are used to complete in 2D the areas that are not modeled but whose display aids in showing design intent. For instance, you might add 2D earth hatching around a foundation footing.

    As the name implies, view-specific elements exist only in the view in which they are placed, with dependent views the exception to the rule. Dependent views are child views to a single parent view and share all view-specific elements with the parent and its other children.

    An example of a dependent view is a large framing plan that needs to be divided into several sections so it will fit onto your title sheet. If you add view-specific components to the parent view, they will also appear in the child views, which allows you to work in an overall plan view of the building without the added burden of placing annotation in each partial view.

    Model elements, on the other hand, appear in every view whose extent they intersect. That saves a lot of time and coordination effort when you are making significant changes in the design. And remember: you can work on the model elements in any view in which they appear.

    Discuss this article in the Architecture Forum...

    Thomas S. Weir is director of BIM and CAD operations at Brandow & Johnston in Los Angeles. He is co-chairman and founder of the L.A. Revit Users Group, moderates the Autodesk User Group International (AUGI) Revit Structural forum, teaches Revit Structure at Autodesk University, and wrote the first Autodesk Official Training Courseware for Revit Structure.

    Jamie D. Richardson is an associate and CAD/BIM Manager for Ericksen Roed & Associates in the Twin Cities area. He speaks at Autodesk University, is active in his local Revit User Group, and mentors students at local technical colleges.

    David J. Harrington, former president and former board member of AUGI, is currently a structural designer for Walter P Moore. He writes for industry publications, is the technical editor for AUGIWorld magazine, teaches at Autodesk University, and maintains the popular blog CADDHELP.

    This article is excerpted from Mastering Revit® Structure 2010 by Thomas S. Weir, Jamie D. Richardson, David J. Harrington, copyright © 2009, with permission of the publisher, John Wiley & Sons.



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    Some interactive three-dimensional model viewing is also supported in Revit Structure 2010.
    Image: Courtesy John Wiley & Sons

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    Saved views are managed within the Revit Structure "Schedules" menu.
    Image: Courtesy John Wiley & Sons

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    Revit Structure supports component libraries, like this family of columns included with the software.
    Image: Courtesy John Wiley & Sons Extra Large Image

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    A variety of beam shapes can be created by extruding object sections from the library along virtually any common 2D object type.
    Image: Courtesy John Wiley & Sons

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    Detailed properties of a structural object can be displayed and edited.
    Image: Courtesy John Wiley & Sons

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    Revit Structure can display model elements at any of several levels of logical abstraction.
    Image: Courtesy John Wiley & Sons Extra Large Image

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    Although Revit Structure's underlying BIM model allows changes to propagate automatically to any view on any drawing sheet, the sheet creation and individual drawing placement is achieved manually.
    Image: Courtesy John Wiley & Sons

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    Mastering RevitŪ Structure 2010 by Thomas S. Weir, Jamie D. Richardson, and David J. Harrington.
    Image: John Wiley & Sons Extra Large Image


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