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Figure 2.11 Lateral brace frame
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defining loDs or assigning the proper personnel to operate the tools. in the sidebar
“the Dangers of Undefined loD,” who is at fault? the owner had “virtual modeling”
in the requirements for design and construction but didn’t define loD. the project manager relied on the structural engineer’s model and assigned an inexperienced intern to run coordination. the mechanical subcontractor didn’t review the structural drawings to route his duct. the mechanical engineer approved the drawings. a number of people could be at fault, but in the end everyone loses. the more BiM is used and relied on for drawings and system coordination, the more important it will be to clearly define expectations and align the loD requirements during the design and construction phases (see Figure 2.12 for a sample loD matrix).
clash test, the mechanical detailer provides shop drawings to the mechanical engineer to review and approve. The shop drawings are approved and installation begins in the field.
As the steel is being erected, the mechanical subcontractor comes into the jobsite trailer and asks, “What are those kickers for?” “Kickers!” the intern exclaims. The intern goes out to the field and realizes that there are kickers in the beam pockets where the mechanical contractor had routed his duct. He goes back to the trailer to look at the model. “There’s nothing shown,”
he says. He decides to open up the permit set of structural drawings sitting under his desk that have now collected a nice layer of red dirt from the jobsite. He flips to a plan view and notices that there’s a 2D annotation for kickers in multiple places on the floor and it references Figure 2.11.
His stomach turns into knots. The structural engineer had used a hybrid approach to create the construction documents; modeling major structural components but annotating the kickers at LOD 100. The mechanical duct has no option but to be lowered due to the kickers, so an RFI is drafted and an unhappy owner is faced with lowering the beautiful 12‐foot ceilings to 9 feet.
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Model-Based Scheduling
another common use for BiM is tying the model (design or construction) to a schedule to animate the sequence of work and display where a project should be at any given time. this has become a common tool for selling work to owners, looking at logistics of construction for efficiencies and safety, as well as throughout construction for justifying subcontractor billings to the owner for completed work. the reason this has become such a popular feature of BiM is its ability to give immediate clarity to all stakeholders in understanding the project schedule. typical gantt chart schedules can be hard to understand, but when you watch a simulation of the building being built, the logic becomes more tangible.
loD plays a role in this use depending on the scheduling methodology (critical Path Method, line of Balance, etc.), but the aia e203 basically says that you can have more precise model-based schedules as the model becomes more precise. While, that’s right: the more developed the model, the more detailed your schedule simulation can be. you could show the bolts going in if you wanted to. however, the potential return on the time investment required to link model elements to the schedule diminishes at a certain level of detail.
Model-based scheduling can be used at all stages of the project, whether it’s during conceptual design to discuss site logistics or used during construction for demonstrating the sequence of work and validating costs of completed work. it doesn’t require a high skill set to create model-based simulations, but it does require a competent person who understands the sequence of construction and scheduling logic. For this reason, it is important to integrate personnel who can achieve both into the project team.
Model-Based Estimating
Model-based estimating has been redefined over the past five years. originally, it meant that the model-based schedule had costs associated with the elements so it could track time and cost with the animation. the owner would be able to know the exact amount the contractor should be billing at any given time, provided the subcontractor’s scope was quantified in the model. although this method can still be used, more companies use model-based estimating in the form of a takeoff. this is where you use the model to extract quantities of materials and associate costs with those materials for estimating purposes.
Using the model for cost estimating should be handled with the same caution as model-based coordination. the loD has to be defined before you can rely on the model for accurate estimates. you can use the same scenario we considered earlier with the kicker example. if the structural engineer delivered the hybrid loD model and you used it to extract quantities of steel, your estimate would be off by the cost of every kicker required on the project if the model was the sole source of information. Similar to model-based coordination, experienced personnel in both the technology and in
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Model-Based Facilities Management
Model-based facilities management focuses on leveraging the model information to reduce the owner’s costs over the life cycle of a structure (see Figure 2.13). a common figure that is used to describe life-cycle cost of a building states that around 20 percent of life-cycle cost is designing and building and 80 percent is operating and maintaining.
Design and Construction Cost Operations and Maintenance Cost 20%
80%
Figure 2.13 Life‐cycle cost of a building
that means that there is a high level of importance in making the structures as efficient as possible when it comes to operations and maintenance. hypothetically, in the kicker example, information could have been added to the actual weld element, shown in the loD 400 example in table 2.3, describing it as a fillet weld that needs to be done by a certified welder using e70XX electrodes and that should conform to the latest revision of the american Welding Society’s D1.1. additionally, hyperlinks could have been added to approved websites that sell equipment and to a youtube video of a worker creating a fillet weld.
the model has unlimited potential to contain all of that information. apply that same scenario to a light fixture, though. a building can contain hundreds of different light fixtures that are constantly being replaced throughout the life cycle of a building.
if the fixture in the model had the serial number, manufacturer, warranty information, bulb requirements, instructions for ordering the bulb, and a video of someone replacing the bulb, then it might not seem so ridiculous, mainly because it is applicable. the information contained within a model can be helpful in reducing costs associated with maintenance and is less likely to be misplaced, deteriorate, or get coffee spilled on it like paper documents. (these concepts will be covered more in chapters 6 and 7.)
Note:
There’s another important lesson to be learned in this example on LOD. In the “Caveats” section of the BIMForum’s “Level of Development Specification,” they state that “there is no strict correspondence between LOD’s and design phases. Building systems are developed at different rates through the design process. For example, design of the structural system is usually well ahead of the design of interior construction.” This means that the structural steel model could be at LOD 400 the same time the architectural model is at LOD 300. They go on to say that “there is no such thing as an ‘LOD model.’” In other words, the architectural model could have doors at LOD 200, ceilings at LOD 300, and walls at LOD 350.Chapter2:Project Planning ■
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can you imagine how cumbersome it would be for architects, engineers, and subcontractors if they had to put all that information into every element in the model?
loD can be misinterpreted this way, and when it is, it becomes ridiculous. For this reason, it is important to understand the purpose of an loD matrix. it allows the owner to define and organize what elements require a certain level of information for use in the life cycle of the building at the onset of a project with the BiM addendum. once these elements are identified, it is necessary for the aec firms to align with one another and collaborate with the facilities director on how he or she will leverage that information for maintenance and operations of the building. this collaboration is necessary to make sure that the information contained within the model and related linked database are delivered in the right format to communicate with the building management software.
Note:
Model-based facilities management is not a click‐of‐the‐button process, nor is it typical of most projects, so it requires a high level of expertise. It’s a best practice to get the team involved early on to set clear goals for how the model will inform facilities management, and may require a third‐party expert to assist in outlining the procedure in the contract or execution plan (discussed later in this chapter). Writing “all trades are to deliver LOD 400 models” or “the model will be used for facilities management” in a contract is just as open‐ended as writing “virtual modeling” as a requirement.Model-Based Analysis
Model-based facilities management is often driven by the financial cost to the owner, whereas model-based analysis has more to do with the qualitative costs to the tenants and the environmental costs to our planet. there are some aspects of this analysis that will reduce financial costs to the owner in regard to operation fees, but sustainable designs aren’t always the most maintenance-friendly solutions.
For example, windows are proven to promote better production and health among tenants through natural daylight (qualitative costs). in order to have more daylight, you have to have more windows. if you have more windows, there will be more window-cleaning costs (financial costs). the idea, however, is that if the building is designed and analyzed properly, the operational savings far exceed the cost of maintenance for a few extra windows. BiM can play a key role in this analysis.
During conceptual-schematic design, an architect can create simple models at loD 200 to analyze the location of the site, orientation of the building for heat gain, wind direction for natural ventilation, and the shape for daylighting indoor spaces. once the conceptual design is vetted out, the model can then be further enhanced with information for material selection, mechanical systems, and electrical systems, which often push the loD to 300–350. this information is required to analyze loads and project how much energy will be required for a building to operate and keep the tenants comfortable.
that analysis is an ebb and flow between the designs of the architect, electrical