Building information models can be specified and articulated with great clarity at various stages of the design and construction process according to the Level of Development (BIM LOD) Specification.
The Specification is a thorough interpretation of the Level of Development (BIM LOD) schema created by the American Institute of Architects for its E202-2009 BIM and Digital Data Exhibit and updated for its G202-2013 Project. It defines and illustrates the characteristics of model elements of various building systems at different Levels of Development and is organized in accordance with CSI Uniformat 20103. Its goal is to standardize the BIM LOD framework's usage and aid in its explanation so that it may be used more effectively as a communication tool.
It is crucial to stress several issues here since the BIM LOD Specification follows the LOD schema's design goal as published by the AIA.
BIM LODs and the Design Phase:
The design phases do not define the BIM LODs. Instead, the LOD language can be used to define the completion of the design phase as well as any other milestone or deliverable. This strategy is advantageous for a number of key reasons:
1. The design phases do not presently have any defined standards. Many architects have developed internal standards, however they vary from one company to the next, and requirements are occasionally modified even within the same firm to meet the needs of a specific project.
2. Different elements will be at different positions along the building system evolution at any given moment because different building systems progress from concept to precise definition at different speeds. For instance, the model will have numerous pieces at LOD 200 after the Schematic Design phase is complete, but it will have many elements at LOD 100, some at LOD 300, and perhaps even LOD 400.
BIM LODs and model definition:
Project models at any stage of delivery will necessarily contain components and assemblies at various degrees of development. For instance, it makes no sense to demand a "LOD 200 model" once the schematic design stage is complete. The "100% SD Model" will instead include modeled features at different stages of development.
Definitions of LOD:
With two exceptions, the BIM LOD definitions used in this Specification are the same ones published in the AIA's revised Digital Practice Documents.
1. The working group first recognized the necessity for a BIM LOD that would describe model components sufficiently developed to allow for detailed coordination amongst disciplines, such as clash detection/avoidance, layout, etc. This level was given the designation LOD 350 since the requirements are higher than those for level 300 but lower than those for level 400. LOD 350 is not present in the AIA publications, although it is mentioned in the related Guide and Instructions.
2. The working group did not believe it was necessary to further describe and illustrate LOD 500 in this Specification because it relates to field verification, even though it is contained in the AIA's LOD definitions. As a result, LOD 100–400 is the only range covered by the enhanced descriptions and graphic illustrations in this Specification.
BIM LOD as a Tool for Communication:
When a BIM LOD is used as a medium for communication or collaboration, that is, when someone other than the author extracts information from it, a number of concerns come up that are addressed by the LOD schema:
1. Building systems and components move from a general basic idea to a detailed description during the design phase. There has never been an easy way to indicate where a model element is along this journey before. The author is aware, but others frequently aren't.
2. It is simple to misjudge the level of accuracy at which an element is modeled. The level of precision in a hand drawing can be deduced from the drawing's appearance. Hand drawings can range from rough pen strokes on a napkin to hard lines with dimensions written out. However, in a model, a generic component positioned roughly can appear identical to a specific component positioned precisely, thus we need something other than appearance to distinguish between the two.
3. Unconfirmed dimensions can be measured precisely, assembly information frequently exists before it is finalized, etc., so it is feasible to infer or extract information from a BIM that the author did not intend. The LOD framework enables model authors to clearly state the reliability of given model elements.
4. The design work plan assumes great importance in a collaborative setting when individuals other than the model author depend on information from the model to advance their own work. This is because model users need to know when information will be available in order to plan their work. The LOD framework makes this easier.
The BIM LOD Framework solves these issues by providing an industry standard to describe the state of development of various systems, assemblies, and components inside a BIM. This standard makes it easier to precisely define BIM deliverables and milestones, promoting consistency in both communication and execution. To know more, contact Tejjy Inc BIM consultants in USA at 202-465-4830 or info@tejjy.com.