LOD Specifications for Structural BIM Processes: Defining Model Elements and Content Requirements
The key benefit of BIM is that it allows structural engineers to share the digital model of a structure with the contractors and fabricators. It also brings the engineers and their design teams closer and enables them introduce improved collaboration and coordination.
It is very important for engineers to develop the models with high level of clarity and reliability for various stages of structural design, fabrication and development.
Here, Level of development specifications comes into picture.
Today, structural engineering contract scopes are well defined due to the introduction of level of development (LOD) specifications from 100 to 500. All structural models are not detailed to a certain specific LOD. For example, it cannot be said that a structural model is LOD 300, or LOD 400.
A structural 3D model is a mix of various levels of development for various components:
- The columns and beams for a structural model can be developed for LOD 300, while other constructible components and elements that require higher amount of detailing, can be at a higher LOD such as 350 or 400.
- Level of development ranges from 100 to 500, and structural engineers need to decide, exactly which level of development they require for all components.
- Structural engineers can simply reference the structural information for LOD 100 by writing a short narrative.
- Hence the vocabulary of the structure gets defined. At LOD 200, the objects, assemblies and other generic systems are shown with approximate quantities, dimensions, shape orientation and location.
- As the specified level of development reaches LOD 500, the models are populated with non geometric information and this information.
However, this information is typically useful for facility owners and managers – i.e. after the building is ready to be occupied.
Structural engineers typically require LOD anywhere between 300, 350 and 400.
- At LOD 300, details regarding the exact dimension, location and orientation – appropriate for permanent sets of permit drawings are populated.
- At LOD 350, model elements contain information for cross trade coordination, and construction layout. These models contain details that are typically included in construction drawings. These are full fabrication models, and they bring clarity to the design and construction process.
- With LOD 400 specification, higher level fabrication models are prepared with complete detailing, fabrication, assembly and installation information.
Structural engineers are increasingly demanding for models with greater details. The BIM technology advancements hence empower structural engineering firms, by lowering the involved risks. If, the models that are sent to the contractor are accurate and have the required fabrication detail, these constructible 3D models provide both engineers and contractors, enhanced control over the project, and hence reduce risks and liabilities.
Better control over projects with constructible structural 3D models will not only reduce risks, but also enable improved coordination between building owners, design teams, general contractors, and the structural engineers, resulting in cost reduction.
Often engineering firms and independent structural engineers do not have the in-house capabilities to develop BIM with the required LOD. Joining hands with BIM experts and outsourcing service providers, can help them develop models with design, fabrication and installation information and communicate the same with contractors.
Just the right amount of details and level of development specifications, translates into successful design communication and coordination between teams. This in turn enables engineers to decrease the time in design and development phase. Besides, any issues in the structural design can be easily identified and revisions can be efficiently tracked. All this, translates into development of high performing and safe structures.