In simple, BIM allows for virtual construction of a building to its full details. How this has been made possible is through the global BIM initiatives which are currently lead by buildingSMART. The background of the BIM (specifically the openBIM) technology is discussed above. Several proprietary BIM solutions are also developed to scales not yet matched by IFC (of buildingSMART) probably due to the competition and large budget allocation for R&D as a result of that. However, these developments are usually within limited scope in contrast to wider scope of buildingSMART initiatives.
The objects within BIM are termed “intelligent” because of defined properties and behavioural relationship with other objects. A door knows that it is a door, and when it is placed into a wall the wall knows it has to have an opening to suit that particular door. The parametric properties are inter-related. If the door size is changed, the wall opening will change to suit. All of the physical and functional characteristics of the building model are held in the central database. As the model develops, all of the objects within it parametrically adapt themselves to the new design. These models are therefore rich in information that can be extracted and used for a variety of analyses to assist in design, construction and operational optimization [read Lovegrove].
BIM technology brings in numerous advantages for designing, construction management and cost estimating of building projects. However, it should be noted that BIM may also bring various limitations to the process, which may have been already realized or yet to be realized. Nevertheless, it is evident that limitations get diminished with the advancement of technologies.
Traditional CAD versus BIM
A computer graphic is usually a Raster Image. A raster image is made up of large number of tiny coloured dots (called piexels) which generate the image for the viewer. This is the common type of graphic generated by digital cameras and scanners.
Traditional Two-Dimensional (2D) and Three-Dimensional (3D) Computer Aided Draughting (CAD) programmes made use of geometrical primitives such as points, lines, curves and shapes or polygons, which are known as vectors. Vectors are based on mathematical equations. They lead through locations called control points. Each of these points has a definite position on the x and y axes of the work plane. For 3D graphics, a third axis z is added. Vector generated images are called Vector Graphics. 3D rendering (image generation) in vector graphics uses polygon fill to get the solid state appearance. However, the elements in fact do not have solid state characteristics (i.e. they are not machine readable as solid). There were other 3D authoring applications which could add parameters such as weight and friction to 3D elements, but were widely used in 3D animation industries.
BIM essentially does not require graphical interface. Industry Foundation Classes (IFC) is plain text database readable in any standard text reader. In order to interpret the text, one must know the relevant information schema. Still, the effort will become worthless because even the IFC file of a small building is near infinitely lengthy that makes it far beyond human cognition. However, since geometry is one of the parameter of a BIM element, software applications can generate vector graphics or raster images by reading BIM data. Advanced tools are developed which enables the designers to design buildings in a virtual 3D space without requiring them to have any knowledge on IFCs. Similarly, there are many other software applications developed with interpreters built-in in order to perform various tasks for design, development and lifecycle management of buildings. Some applications read and author IFCs, while others only read them to interpret information for tasks such as those in facilities management.
It should be noted that BIM is not an evolution 3D CAD modelling. Instead, it is s new breed of modelling. Thus, it is not possible to say that BIM is better than 3D CAD in terms of all aspects of 3D CAD. Whether BIM allows same level of flexibility of traditional CAD for designers is yet to be found [read Lockley].
Construction management with BIM
Construction Scheduling is known as 4D BIM, since time is considered to be the fourth dimension of an element. 4D BIM is about use of BIM technology for construction project visualization (often in virtual 3D) and CPM scheduling. Associated processes such as supply chain management, procurement management, and risk management, are also considered within 4D BIM.
A highly welcomed feature of BIM in terms of construction management is Clash Detection. The word "clash," will bring to one’s mind of pipes running into HVAC and cutting through a floor. Identifying and fixing these issues ahead of time has been one of the best uses of BIM technology. While been a useful feature during design phase, clash detection become invaluable when dealing with changes and unexpected physical conditions.
Clashes will not only occur in design, there can be other clashes such as scheduling clashes where too many labour gangs are required working in a limited space. The BIM and allied technology has been advanced to detect all these 2D, 3D and 4D clashes in project execution [see Vico Soft]. Technologies are further extended from linking BIM models with popular project management software to subcontractor evaluation and management.
One of the barriers envisaged getting BIM to the worksite where parties of various financial calibres take-part, was the affordability of the technology. This is thought to be insignificant now since there are affordable (or sometimes free to use) software available for using BIM at site level [see Tekla BIMsight].
BIM and Cost Estimating
The next parameter considered for incorporation to BIM is the cost. Thus, cost estimating with BIM is known as 5D BIM. However, there is no evidence of real integration of cost estimating into BIM. While “Cost” is a standard property of a BIM element, there is no popular usage of it for cost estimating. The possible reason is that summation of cost of elements would not yield the total cost, since there are many other parameters affecting the cost. What is evident is the development of tools for automation of quantity takeoff process by reading (interpreting) the BIM models and employ them in the conventional estimating process, which may also be partly automated. However, some are intuitively advanced that the estimate (or cost model) is visually linked to the 3D model view. For example, when a cost item in the schedule is selected, relevant building elements are highlighted in the 3D visual model [see Nomitech and Exactal]. While most of BIM cost estimating tools can only read BIM models, there are some estimating tools which can write back to BIM models updating its cost properties [see Beck Technology].