什么是BIM?

  “BIM”指建筑信息模型(Building Information Modeling),是一种建筑行业信息化方案,也是建筑行业的发展趋势。目前,有些软件都开始宣称其支持BIM功能,那么到底什么是BIM呢?

  下面引自美国佐治亚理工学院Chuk Eastman教授的一篇文章,很浅显地讲述了BIM的概念,由于篇幅较大且也比较易懂,就不翻译了^_^

BIM is a huge buzzword in AEC. It shows up in every magazine; there are multiple conferences a year about it; software developers headline their products as BIM tools. What is it? How is it different? Why should an architect or contractor care about BIM?

What BIM is and Why is it Different?
For all of the history, design and construction of building have relied on drawings for representing the work to be done. They were defined as contracts - legal documents, were assessed by building codes, and used to manage the facility afterward. But there are two strategic limitations of drawings: (1) they require multiple views to depict a 3D object in adequate detail for construction, making them highly redundant and thus open to errors; (2) they are stored as lines, arcs and text that is only interpretable by some people, they cannot be interpreted by computers.

BIM involves representing a design as objects - generic or product-specific, solid shapes or void-space oriented (like the shape of a room), that carry their geometry and attributes. The geometry may be 2D or 3D. The objects may be abstract and conceptual or construction detailed. Composed together these objects define a building model. If an object is changed or moved, it need only be acted on once. BIM design tools then allow for extracting different views from a building model for drawing production and other uses. These different views are automatically consistent - in the sense that the objects are all of a consistent size, location, specification - since each object instance is defined only once. Drawing consistency eliminates many errors.

Modern BIM design tools go further. They define objects parametrically. That is, the objects are defined as parameters and relations to other objects, so that if a related object changes, this one will also. Parametric objects automatically re-build themselves according to the rules embedded in them. The rules may be simple, requiring a window to be wholly within a wall, or complex defining size ranges, and detailing.

Why BIM is Important
Because 3D objects are machine readable, spatial conflicts in a building model can be checked automatically. Because of this capability, at both the design and shop drawing levels, errors and change orders due to internal errors are greatly reduced. Thus as a building representation, BIM technology is far superior to drawings.

But the larger implications are not just consistent drawings and clash detection. Because building models are machine readable, it becomes practical to use that data in many other ways: to generate bills of material - that can be used for cost estimation or automatic ordering and tracking, for energy, lighting, acoustic or other analyses - not as post facto checking if an almost finished design is "OK", but rather to provide feedback while designing, informing the designer of the effects of changes. Thus building models allow for better integration of many processes, allowing the kind of tracking and control that computers allow in manufacturing and your local grocery or department store, tracking every item from creation to delivery. Many of the uses of BIM data are waiting to be discovered and developed.

While building modeling first gained popularity because it was the only way to get blob buildings and exotic forms constructed, big payoffs can be gained for even simple buildings. Building models can save costs, save construction time, and support better building performance and control. It can potentially beneficially impact all parties in the construction process - designers, engineers, contractors, fabricators, facility operators. the whole construction industry. In this sense, BIM is similar to the automation of manufacturing in the 1980s, when most manufacturing industries first adopted 3D modeling and digital representations. The changer of ways of operating in manufacturing are still evolving.

These capabilities also facilitate much improved coordination and collaboration. Designing a building once for contract drawings, then developing a set of detailed drawings for shop fabrication later is recognized as involving much waste and inefficiency. Design-build and other forms of architect-contractor teaming have been recognized as more efficient - in terms of cost, time, and for reducing the potential for litigation. Building models tremendously facilitate this process. A 3D model is easier for all parties to interpret and visualize. Design or fabrication work can be coordinated in person or at a distance using web conferencing tools such as Webex and GoToMeeting and virtually walking through the 3D model.

Definitions of "BIM"?
Some people have called the building model "a BIM" - that Revit or ArchiCAD or Bentley generate a BIM. Others say that the representation is not as important as the process of going to machine readable model(s) because machine readability opens up so many opportunities for further integration. Above, I have referred to a building model as the basis for BIM, and implied that BIM is a process. This definition is consistent with that outlined by GSA, on their BIM website, at: http://www.gsa.gov/bim The process of BIM is revolutionary because it provides the opportunity to migrate from practices that are centered around human craftsmanship to a more augmented and modern machine craftsmanship - and all that this might imply.

Will it Become Standard?
BIM tools are as different from CADD tools as are a slide rule from a computer, as different from a set of toy soldiers to a battle-oriented computer game. BIM supports on-line simulation of a design, on-line simulation of construction - called 4D CAD. The BIM processes provide better building products at lower costs to the owner. Early case studies have shown these benefits by users who have applied BIM well. It will certainly become the standard for construction within most of our lifetimes.