BIM at LOD400: Why Level of Development 400 matters for design and virtual construction
Today’s fast-paced world of design and construction is fractured. Risk aversion, shortened construction timeframes, and more complex projects are creating a gap of information between what was designed and what should be built, costing time and money.
At Walter P Moore, our solution is to solve design virtually, by producing a building information model (BIM) at Level of Development 400 (LOD400). By broadening design to anticipate construction issues and delivering a fabrication-ready model, engineers can create more certainty in cost, schedule, and design intent.
Nearly 50 years ago, Boyd Paulson created a simple yet powerful rubric for understanding the relationship between the influence of decision-making for project outcomes versus the committed project costs. The following holds true for every project every time: over the course of the project schedule, the influence to change outcomes steadily decreases, and the committed project costs go up.
By supplementing Boyd’s analysis, at any point in time, the final cost of the project is an uncertain/unknown. It is estimated, but it will not be known exactly until the project is complete. It is this uncertainty that is the breeding ground for risk, unmet cost and schedule expectations, and loss of trust between project partners.
One way to combat this problem is to improve the shape of the influence curve. If engineers can maintain a higher level of influence over project outcomes and hold off on the committed project costs, it is one way to ensure the final cost and schedule better aligns with initial estimates. This article will discuss a method to improve the shape of the influence curve.
What is LOD400, and what does it mean for BIM models?
Over the past 10 years, a number of AEC industry stakeholders have contributed to the development of a common language for BIMs used with increasing frequency and reliance in the industry. The BIM Forum publishes annually a Level of Development (LOD) Specification that provides guidance on the expectations of the BIM for the project. This is performed by applying a numeric value to specific components within the BIM based on the specific criteria those elements satisfy. In general, the higher LOD numeric value, the further along that element is on the spectrum from concept to fabrication ready.
This common language helps reduce barriers to understanding the nature of the BIM, and therefore increases confidence and the right level of reliance by those who need the information in the BIM to construct the building.
In this article, any references to LOD400 are a reference to the definition provided by the BIM Forum (2021 version quoted): “The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of size, shape, location, quantity, and orientation with detailing, fabrication, assembly, and installation information. Non-graphic information may also be attached to the Model Element.”
Here also is the common language interpretation, also from the LOD Specification: “An LOD400 element is modeled at sufficient detail and accuracy for fabrication of the represented component. The quantity, size, shape, location, and orientation of the element as designed can be measured directly from the model without referring to non-modeled information such as notes or dimension callouts.”
It is clear the definition LOD400 represents elements that are fabrication ready. All information sufficient to fabricate the element is contained in the modeled element. This exceeds the LOD of a BIM element universally accepted by the design industry as acceptable for permit-level documents. The modeled elements are not merely sufficient for bidding, procurement, or mill order. The modeled elements are ready to be fabricated.
A snapshot of the industry today shows that different building elements are advanced to various LOD endpoints prior to fabrication. Further, certain structural elements—reinforcing steel, for example—are frequently not even modeled before they are fabricated:
- Structural steel: estimated greater than 90% modeled before fabrication
- Rebar: estimated 10% or less modeled before fabrication
- Light gauge steel: estimated 5% or less modeled before fabrication
Why the disparity? It is speculated this is due to necessity being the mother of invention. For each structural material, the specific elements themselves benefit variably from an LOD400 in order to be fabricated. For instance, connecting a steel beam or brace to a steel column benefit from all the specific elements—the beam, the column, the connecting plates, the welds, the bolts—being modeled to a fabrication level.
Conversely, specific pieces of reinforcing steel do not have such demanding connectivity requirements—or frequently zero connectivity requirements—and therefore there is little advantage gained per bar by modeling individual bars versus fabrication based on a 2D bend diagram drawing.
What are the benefits of LOD400? Let’s look at ‘first order benefits’
“First order benefits” are those that provide value to the single trade or structural material directly. One has been discussed already: determining intra-trade connectivity requirements.
To understand other benefits, below are two additional examples:
- Bringing the structural steel to LOD400 yields the first order benefit of preserving design intent. A structural steel frame used as part of a new baseball stadium will be exposed to view in the permanent condition. Therefore, multiple stakeholders—the owner, architect, sponsors—will care about the aesthetics of the frame: its columns, beams, braces, and connecting elements. Bringing these elements to LOD400 will give the stakeholders a realistic and comprehensive understanding of what these elements look like as well as the ability to iterate/adjust them through the design process. This process allows more control over the design intent of these elements and minimizes the risk that the final product will not align with this design intent. There will be significantly reduced uncertainty by the steel fabricator for what is required to satisfy the design intent and provide the owner what they expect to see once the project gets built.
- Building virtually at LOD400 yields the first order benefits of revealing accurate levels of complexity and reducing risk during construction. A new high rise utilizes concrete shear walls as the lateral load-resisting system, arranged around the elevator bank in the central core of the building. Such shear walls will have elevator and MEP openings at nearly every level. The wall areas around such openings, including the link beams over the elevator openings, are typically among the most complex and congested areas of reinforced concrete on the entire project. An LOD400 model of the reinforcing in this area yields a better understanding of this complexity, and therefore provides more opportunity to plan for how to manage it once the project goes physical. Furthermore, modeled reinforcing will immediately reveal if the area is too congested—if bars are clashing with each other—and can serve as a platform for resolving such problems. This process of figuring out the project will happen either way: either in the field, or, preferably, in the model. When it is in the model, this process is called “virtual construction.” In this case, bringing the reinforced concrete to LOD400 yields two first order benefits: revealing an accurate level of complexity to the work, and providing an opportunity to perform virtual construction, which is less expensive, faster, and less risky than physical construction.
‘Second order benefits’ of LOD400
“Second order benefits” are those that provide value to multiple stakeholders beyond the single structural trade. In these cases, in combination with other adjacent services on the project, the combined impact of an LOD400 model yields arguably greater advantages to the sum of the stakeholders than the benefit to the relevant trade. Specifically, when the creation of an LOD400 model occurs as an overlay of the structural design, several benefits accrue to the team.
Traditionally and per typical contracts on the design side, the Engineer of Record only needs to issue designs for these and indeed any portion of the structure, at such a time as when they are prepared to affix their seal to their design documents. Now, whether that is consistent with a presumed construction schedule, prepared and managed by others, is uncertain.
However, the issue is that the owner cares about the schedule. It is one of three essential values to the owner of any project: the design, the cost, and the schedule. Additionally, the pace of project schedules is only going one direction—faster. The shorter the project schedule, the more chance that a disconnect in the design and construction activities will not just appear but become problematic and sometimes intractable. This is the breeding ground of additional cost, schedule delays, unmet expectations regarding the final outcome, and, many times, litigation.
Time is such a precious commodity that it is hard to imagine project schedules slowing down. Therefore, a solution must be found that reformats project delivery into something that looks different than the past.
How can the LOD400 BIM model help project teams?
Faster Schedules
Simply put, it is possible to overlay the creation of the LOD400 with the development of the design. In many cases an LOD400 will form the basis of the fabrication because it represents, at some point, a step on the critical path of the project. Therefore, starting these activities earlier in the project schedule allows them to end earlier in the project schedule. The time savings drops to the bottom line.
Reduced Risk to the Schedule
This is related to the first benefit but is slightly different. When a structure has been brought to fabrication level, it represents a form of “virtual construction.” When the requisite technical expertise has been brought to bear—engineering, constructability, etc.—then the end product LOD400 represents the “first construction” of the project. Because it has been done in a virtual environment—where the structure can be moved, supplemented, or even wholesale deleted—it is dramatically less risky to work through “figuring the project out” in this way, versus in the physical environment.
No one wants to show up on a job site where objects are clashing with each other. This is a recipe for disaster in terms of time, money, re-design, and the like.
When the structure has already been built once, the team has greater certainty on how the project will proceed the second time, i.e., the “physical twin” of the structure. This is what is meant by reduced risk to the schedule – the entire team has greater certainty in the schedule once the project goes physical.
Walter P Moore’s experience indicates that for the large majority of projects, certain aspects of the structural design are known, or at least can be known, earlier in the project timeline than others. Infill composite steel beams and pad footings supporting gravity columns are two simple examples of elements that can be built first virtually to add speed to the schedule.
Tighter Bids
As a general rule, the greater the unknowns that exist on a project, the increased number of assumptions contractors and subcontractors need to make when preparing their bids. The project is open to more interpretation. Sometimes this can be beneficial, such as when a subcontractor conceives of a novel way to develop the means of construction. The resulting winning bid provides value to the owner. But whatever advantage exists by leaving certain elements up to the subcontractor to figure out is more than offset by the risk that the design intent has not been understood by those who need to execute it.
However, if trade partners are provided an LOD400 model they can use to prepare their bids, the volume of information they can use to inform their price and schedule increases substantially. There is very little room for misunderstanding design intent. Quantities and level of complexity can be understood readily from the model, sometimes through automated queries. As a result, there is less risk that the low bidder has missed an important piece of the scope that will eventually need to be part of the built project, or that the high bidder had cost or schedule to cover a piece of scope that was not actually required.
Facilities Management
Creating a model at LOD400 has benefits to the structure long after construction. Facility managers can use the information within the model to more accurately space-plan to create the best use of space available, which can aid in real estate expense efficiency.
Additionally, the level of detail provided in LOD400 can aid in asset management of building equipment and systems through planning regularly scheduled maintenance, durability, and life cycle management.
Today’s construction projects are moving at a faster pace, with more complexity. While creating an LOD400 model at the outset may seem to increase costs and time spent in design, the benefits have repeatedly proven to outweigh these issues, providing significant cost and schedule savings along with reduced risk.
About thr Author:
Stephen E. Blumenbaum, PE, SE, is a Senior Principal and Director of Construction Engineering at Walter P Moore. He can be reached at [email protected].