BIM technology is built upon computer-aided design (CAD) technology and continues to evolve from this foundation. However, there are still significant differences between CAD and BIM, which can be summarized in five key points:
1. Dimensionality: CAD primarily involves two-dimensional design, whereas BIM is inherently multidimensional, starting from three dimensions. By adding the element of time, BIM extends into four dimensions, and by incorporating cost factors, it further expands into five dimensions.
2. Software Composition: CAD typically relies on a single drawing software to address design tasks. In contrast, BIM encompasses a wide range of software, including core modeling tools, BIM scheme design software, geometric modeling interfaces, sustainability analysis, visualization tools, structural and electromechanical analysis software, clash detection, detailed design, model inspection, cost management, and operational management applications.
3. Form and Function: BIM facilitates dynamic, multidimensional, and integrated information modeling, while CAD is limited to static, two-dimensional planar graphics.
4. Collaboration: BIM supports interdisciplinary collaboration among various professionals and stakeholders. CAD, on the other hand, is primarily a standalone tool that lacks coordination capabilities.
5. Project Lifecycle Management: BIM supports managing the entire project lifecycle, from design through construction to operation. CAD is generally limited to use during design and construction phases only.
Using examples makes it easier to understand the differences between CAD and BIM technologies. In everyday life and work, we often use Word and Excel software. Think of CAD as Word and BIM as Excel. The difference between CAD and BIM is similar to the difference between Word and Excel.
Consider a salary slip, which includes base salary, performance bonuses, welfare subsidies, social insurance and housing fund deductions, and the actual salary paid. The numbers in Word and Excel might look the same, but if a value changes in Excel, the actual salary automatically updates because the formula linking these components is embedded. In Word, changing a single value does not update the total since there is no relationship between the numbers. In essence, Word shows a static, printed page, while Excel reflects a dynamic, interactive state. Changing one data point in Excel triggers automatic updates in related figures.
During the CAD era, designers created multiple views of buildings—floor plans, elevations, sections, and details—manually. In the BIM era, designers build a comprehensive model from which different views are derived. While individual CAD and BIM views may look similar, BIM allows for changes to be made in one place that automatically update all related views. For example, modifying the size of an electrical conduit in CAD requires adjustments in both plan and elevation views. BIM, however, needs only one parameter change in the model to update all views accordingly.
Beyond plans, elevations, and sections, building design also requires structural, thermal, and energy performance calculations and reviews. In the CAD era, these updates had to be done manually and individually, which was time-consuming and could delay projects. With BIM, such changes are processed quickly and efficiently through automated information collection and integration, greatly enhancing project progress.
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