Introduction
Modern architecture necessitates complex shapes and atypical solutions for structures. With the growing pace in the construction industry, the time allotted for the building design is decreasing, and designers are also required to make quick and prompt decisions. Traditional 2D design techniques do not meet the needs of customers either in quality or in speed. All of these factors contribute to the transition of design organizations to the full cycle of BIM design. In this article, we will figure out how to combine a 3D structural model, a drawing set, and materials estimation in one platform—Revit—and maintain this relationship throughout the entire project.
Concrete Structure Design in Revit
Current Situation
Often, the design of reinforced concrete structures requires the presence of a 3D model of a reinforced concrete frame, which is used for spatial calculation and coordination with adjacent departments. Usually all drawings are developed in AutoCAD using traditional techniques without direct reference to the elements of a 3D model.
How to Organize a Complete Design Cycle in Revit
Revit was created as a tool for complex BIM design with a very flexible interface and tools for modeling and preparation of a drawing set. Moreover, the process of this preparation is more convenient and more logical in many aspects in comparison with AutoCAD.
Design Development (3D - LOD 200 + 2D)
Revit begins to be efficient at the DD stage:
1. The conceptual model is finalized to become the analytical model and is sent to the calculation.
2. At the same time, we are starting to design the basic forms of structural elements in Revit.
3. At the DD stage, there is no need to model the reinforcement and connections in 3D. But this does not mean that we should return to AutoCAD since Revit has a very convenient annotation functionality.
As a result, we get an indivisible BIM model with a drawing set depending on it. We exclude the double work resulting from adjusting the 3D model, the 2D drawings, and all the inconsistencies associated with this.
Construction Documentation and Shop Drawings (3D - LOD 350)
At the construction documentation phase we should properly estimate the volume of concrete, the specific amount of metal per structure, and elements of other connections. To do this, we are developing a 3D model of reinforced concrete structures in the LOD 350.
As a result, we get a detailed 3D model of the concrete frame, a set of drawings, and properly calculated schedules. As a result, when making changes, all the data both in the drawings and in the model and in the specifications remains relevant, which significantly improves the drawing set quality and the entire project.
Construction Support (3D - LOD 450)
We finalize the model obtained during the design process. After that, customers can use it in the construction process:
1. Сonstruction site planning
2. Material requirements planning
3. Сonstruction process superintendence
Possible Ways of Developing Construction Documentation in Revit
We have to divide the structural model in Revit into several links if the building has more than 5,000 square meters (53,000 square feet) in total area. Work files are typically 200-400 MB and should not be more than 500 MB. Otherwise it will be impossible to work even with a powerful and expensive computer.
Free-standing buildings and structures with less than 53,000 square feet (5,000 square meters) in area
As a rule, small buildings and structures in which there are no standard and duplicate elements are developed in a separate file.
Buildings with 53,000-160,000 square feet (5,000-15,000 square meters) in area
Standard elements usually appear in objects with such area, but the number of design participants does not exceed one to three people. To increase the speed of preparation of a set of drawings, we develop and execute drawings for each structural element in a separate file.
There is no need to create sheets, prepare views, draw up drawings, and adjust specifications each time. It is enough to copy an already developed element and make changes.
Buildings larger than 160,000 square feet (15,000 square meters) in area
Work with large objects is characterized by:
1. Large volumes and tight deadlines
2. A large number of participants
3. A large number of standard designs and, as a result, division of labor
There is a need to create a process of "flow design" in Revit. Thus we divide the building into separate files by type of structure (all vertical structures at the ground floor level, all floor slabs of the first floor). Several designers work on each file through Revit Collaboration tools.
This method is considered the most effective: we significantly accelerate the design process and create a single BIM model for coordination with all participants in the design.
Ways of Designing Cast-in-Place Structures in Revit
Going deeper into the topic, we consider 3D practical methods of reinforcing monolithic concrete structures.
The Common Method of Reinforcing Using Standard Revit Tools
Every year Revit developers add more functionality to Structural Rebar. In turn, we widely use this tool in practice, especially during monolithic structures design.
Work with "IFC-rebar" Families
By “IFC reinforcement,” we mean using parametric families for reinforcement. Due to the fact that there are a large number of prefabricated units (cages, mats, embedded parts) in monolithic structures, designers have found a way to create a family of the Structural Rebar Revit category, which can be part of other families.
The use of such parametric families significantly accelerates the work in comparison with the use of Groups and Assemblies and allows you to create combined families of embedded parts.
Combined Method Using Both Common and IFC Methods
Currently, the combined method is widely used. All the reinforcement mounted by individual rods at the site is developed by means of system families, and the prefabricated reinforcement assemblies and embedded parts are made of IFC reinforcement.
Ways of Designing Precast Structures in Revit
I would like to divide the design of prefabricated concrete structures into the assembly of a 3D model of the building frame and the preparation of a set of unit’s shop drawings.
Assembling 3D Models and Installation Drawing
1. To build a 3D model, you must first create a family of concrete unit. An important feature is that at this stage we do not add 3D reinforcement to the family; otherwise, this will make the 3D model heavier to the extent when it is impossible to work even on a high-performance computer.
2. Next, we prepare the installation drawings, draw them up in Revit, and adjust specifications.
3. Joints for connecting the cast units are parametric families, which we additionally place on the installation drawing.
As a result, we have a developed 3D model of the entire building:
• We know for sure that the elements fit together.
• We have a clear idea of what certain design decisions will look like.
• We know exactly how many and what products to put on the construction site.
• We can accurately calculate the number of materials needed to make the connections between the panels.
Development of a Set of Shop Drawings
The development of a set of shop drawings is different from the preparation of installation drawings. A lot depends on the factory of the manufacturer on the volume of output, on whether it is equipped with robotic machines or not, and of course on whether the plant personnel are ready to accept files made in Revit. Two ways to design shop drawings can be drawn from this:
1. 3D—In the event that the customer needs a 3D model, product development is carried out in a separate file in Revit, and drawings for each product are executed in the same file.
2. 2D—In the event that the manufacturer has its own debugged system for creating drawings and files for robotic machines, there is no need to perform 3D reinforcement of products. In this case, we transfer the 3D unit families to the manufacturer, and they, in turn, develop the documentation in 2D.
Cases That Use 3D Rebar More Efficiently Than 2D
From all of the above, it becomes obvious that the full cycle of 3D design is superior in quality and speed to traditional 2D methods. In this case, why is it not widely used in the industry?
Costs of the 3D Work Approach
In order to effectively design reinforced concrete structures in the full BIM cycle, it is necessary to:
1. Have efficient computers and software.
2. Implement BIM technology and staff training.
3. Have accumulated experience, a library of elements and solutions. This experience is achieved by great effort within two to three years. And many organizations and designers give up after the first unsuccessful attempts to implement BIM.
Pros of Working in 2D
1. A wide range of software such as AutoCAD and analogues.
2. A huge baggage of knowledge, which began in the 1990s.
3. Relative simplicity of work in 2D software (for basic AutoCAD training three to five days are enough, while three to five weeks for Revit).
4. The vast majority of modern engineers know how to use AutoCAD. As a result, there is a situation in which it is much easier not to change anything and work the old way rather than to spend energy and money on the study of new technologies.
Is It Worth the Time to Switch from 2D to 3D?
In my opinion, it’s definitely worth it, since with sufficient experience designing in 3D is always faster and more efficient, specialists are highly valued in the market, and organizations have a competitive advantage. The key factor is to gain sufficient experience. If you never try you will never know.
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Nik Makarev holds a bachelor’s degree in Structural Engineering. He is a TrueBIM company leader and author of the Principe for construction designing of large-panel buildings in Revit, author of the Principe for construction designing of cast-in-place concrete building in Revit, and author of the Principe for ventilated façade systems design in Revit. He has three years of BIM engineering experience, two years of BIM consulting experience, and holds a Certificate of Achievement for the successful completion of AEC Building for Technical (June 2018). He is an Autodesk Revit Certified Professional.