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Building Information Modeling (BIM) refers to the process of generating and managing digital representations of physical and functional characteristics of a facility. Generally BIMs are files in proprietary formats containing proprietary data that can be exchanged or networked to support decision-making about a facility. BIM software is used by individuals, businesses and government agencies who plan, design, construct, operate and maintain diverse physical infrastructures, such as water, wastewater, electricity, gas, refuse and communication utilities, roads, bridges and ports, houses, apartments, schools and shops, offices, factories, warehouses and prisons.

The US National Building Information Model Standard Project Committee has the following definition:

Building Information Modeling (BIM) is a digital representation of physical and functional characteristics of a facility. A BIM is a shared knowledge resource for information about a facility forming a reliable basis for decisions during its life-cycle; defined as existing from earliest conception to demolition.

Traditional building design was largely reliant upon two-dimensional technical drawings (plans, elevations, sections, etc.). BIM extends this beyond 3D, augmenting the three primary spatial dimensions (width, height, and depth) with time as the fourth dimension (4D) and cost as the fifth (5D). BIM, therefore, covers more than just geometry. It also covers spatial relationships, light analysis, geographic information, and quantities and properties of building components such as manufacturers' details.

BIM involves representing a design as combinations of objects – vague and undefined, generic or product-specific, solid shapes or void-space oriented like the shape of a room that carry their geometry, relations, and attributes. BIM design tools allow extraction of different views from a building model for drawing production and other uses. These different views are automatically consistent as they are based on a single definition of each object instance.

BIM software also defines objects parametrically; that is, the objects are defined as parameters and relations to other objects, so that if a related object is amended, dependent ones will automatically also change. Each model element can carry attributes for selecting and ordering them automatically, providing cost estimates as well as material tracking and ordering.

For the professionals involved in a project, BIM enables a virtual information model to be handed from the design team (Architects, surveyors, civil, structural and building services engineers, etc.) to the main contractor and sub-contractors and then on to the owner/operator; each professional adds discipline-specific data to the single shared model. This reduces information losses that traditionally occurred when a new team takes 'ownership' of the project, and provides more extensive information to owners of complex structures.

BIM - Project Life Cycle

The use of BIM goes beyond the planning and design phase of the project, extending throughout the building life cycle, supporting processes including cost management, construction management, project management and facility operation.

Following are the application of BIM in the Project Life Cycle:

BIM in Building Management

Building information models span the whole concept-to-occupation time-span. To ensure efficient management of information processes throughout this span, a BIM manager (also sometimes defined as a virtual design-to-construction, VDC, project manager – VDCPM) might be appointed. The BIM manager is retained by a design build team on the client's behalf from the pre-design phase onwards to develop and to track the object-oriented BIM against predicted and measured performance objectives and thereby supporting multi-disciplinary building information models that drive analysis, schedules, take-off and logistics. Companies are also now considering developing BIMs at various levels of details, since to depend on the application of BIM, more or less detail is needed, and there is varying modeling effort associated with generating building information models at different levels of detail.

BIM in Construction Management

Participants in the building process are constantly challenged to deliver successful projects despite tight budgets, limited manpower, accelerated schedules, and limited or conflicting information. The significant disciplines such as architectural, structural and MEP designs should be well coordinated. Building Information Modeling aids in collision detection at the initial stage, identifying the exact location of discrepancies. The BIM concept envisages virtual construction of a facility prior to its actual physical construction, in order to reduce uncertainty and improve safety, work out problems, and simulate and analyze potential impacts. Sub-contractors from every trade can input critical information into the model before beginning construction, and have the opportunity to pre-fabricate or pre-assemble some systems off-site. Waste can be minimized on-site and products can be delivered on a just-in-time basis rather than being stock-piled on-site. Quantities and shared properties of materials can be extracted easily. Scopes of work can be isolated and defined. Systems, assemblies and sequences can be shown in a relative scale with the entire facility or group of facilities. BIM also prevents errors by enabling conflict or 'clash detection' by visually highlighting the parts of the building (e.g.: structural frame and building services pipes or ducts) that may wrongly intersect.

BIM in Facility Management

BIM can bridge the information loss by allowing each group, from design team to construction team and to building owner/operator, associated with handling of a project to add and reference back all information acquired during their period of contribution to the BIM model. This can yield benefits to the facility owner or operator. For example, a building owner may find evidence of a leak in his building. Rather than exploring the physical building, he may turn to the model and see if a water valve is located at the suspected location. He could also have in the model the specific valve size, manufacturer's name, part number, and any other information ever researched in the past, pending adequate computing power. Such problems were initially addressed by Leite and Akinci while developing a vulnerability representation of the facility contents and threats for supporting the identification of vulnerabilities in building emergencies. Dynamic information about the building, such as sensor measurements and control signals from the building systems can also be incorporated within BIM to support analysis of the building operation and maintenance.

BIM Software

Due to the complexity of gathering all the relevant information when working with BIM on a building project some companies have developed software designed specifically to work in a BIM framework. These packages like Bentley AECOsim Building Designer, ArchiCAD, Tekla Structures, Autodesk Revit, VectorWorks differ from architectural drafting tools such as AutoCAD by allowing the addition of further information (time, cost, manufacturers' details, sustainability and maintenance information, etc.) to the building model.

Non-proprietary or open BIM standards

BIM is often associated with Industry Foundation Classes (IFCs) and aecXML – data structures for representing information. IFCs have been developed by buildingSMART (the former International Alliance for Interoperability), as a neutral, non-proprietary or open standard for sharing BIM data among different software applications. Poor software interoperability has long been regarded as an obstacle to industry efficiency in general and to BIM adoption in particular. In August 2004, a US National Institute of Standards and Technology (NIST) report [27] conservatively estimated that $15.8 billion was lost annually by the U.S. capital facilities industry due to inadequate interoperability arising from "the highly fragmented nature of the industry, the industry's continued paperbased business practices, a lack of standardization, and inconsistent technology adoption among stakeholders". An early example of a nationally approved BIM standard is the AISC (American Institute of Steel Construction)-approved CIS/2 standard, a non-proprietary standard with its roots in the UK. There have been attempts at creating a BIM for older, pre-existing facilities. They generally reference key metrics such as the Facility Condition Index (FCI). The validity of these models will need to be monitored over time, because trying to model a building constructed in, say 1927, requires numerous assumptions about design standards, building codes, construction methods, materials, etc., and therefore is far more complex than building a BIM at time of initial design.
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