3D coordination is now used in most projects to help improve predictability during construction. Usually the geometry is only shown in its final constructed location. While it is a big step forward to improving communication and planning, it doesn’t include the space needed during construction—which limits what can be predicted during the construction process. This article will show how to apply a practical approach to 4D construction simulation, including large equipment routing, clear work areas, on-site material storage, and key milestone indicators. We are using a combination of Revit and Navisworks to visualize and animate these important factors in gaining benefit from virtual construction.
4D Construction Simulation
When virtual construction professionals coordinate 3D models, they are taking models representing the final installed position of all components from all trades. 3D coordination only tells part of the story. So, what are we missing? If our ultimate effort is to better understand the construction site, and thus improve schedule accuracy and planning predictability, we aren’t usually coordinating the right thing. I’d even say we may be missing more than half of the story.
3D coordination shows objects in their final installed position. 4D construction simulation shows the objects and space needed during construction.
Separating 4D Fact from 4D Fiction
90%+ of 4D going on in the industry is for show only. Very few examples exist where 4D is implemented in a way that improves communication and on-site efficiency. It is kind of the ultimate “BIM-washing” (still one of my favorite terms). Most commonly this is an animation to demonstrate skill and sophistication in front of a customer during the interview process. Not to disparage selling the value of these technologies as early as possible and to the right people, it just usually never goes further than that.
This article is about making the “show” of 4D turn into a highly practical and valuable tool, easily enabled with 3D BIM to solve very specific problems. We’ll also look ahead at where this foundational construction site coordination can take us.
Use Cases That Can Benefit from 4D Construction Site Simulation
When 3D coordination was initially used to drive construction value from BIM, we didn’t immediately try to coordinate the entire building in 3D. It started with specific tests/use cases. Structure versus architecture, MEP equipment versus structure. Not all aspects of a building could be understood in 3D right away. As with the evolution of 3D coordination, 4D coordination has to start with specific use cases.
Site Logistics Model
Technically this is just another type of 3D model, and can be used in a project timeline simulation, but also can provide value by planning clear work areas looking for trade overlap as well as helping with on-site material storage coordination. These are topics we always covered with customers, but usually as part of a site preparedness guide buried in the detail of a long document. Raising these site coordination topics in a 3D form greatly improves awareness and communication.
Equipment Routing Animation
An equipment routing animation is by far the most valuable and common type of 4D simulation we have offered. It applies to anything that needs to move through a construction site and is only limited by what you can predict about the actual site condition when the installation takes place.
Project Timeline Simulation
The project timeline simulation is the most recognizable and common 4D service, it is also the primary way 4D “fiction” is spread. To date, we have seen limited examples of overall project simulation as a planning tool or as something the actual schedule could be measured against. Real value can be driven from this type of visualization if you consider the other types of 4D we have listed above (site logistics and equipment routing) in addition to adding geometry to visually track tasks or site readiness requirements that cannot be easily communicated in a 3D building model. For this we apply model text that we call a key milestone indicator. These key milestone indicators can be color coded by the construction planner to clarify responsible parties.
Workflow with Revit and Navisworks for Visualizing 4D Construction Site Simulation
Revit is required to perform 4D simulation for the following services.
Site Logistics Model
Revit is where we add objects that represent the areas we need on the construction site, outside of the final installed equipment location. This is stored in a template to be part of a separate 3D model and includes:
Clear work areas
On-site material storage areas
Staging or delivery areas
1. Link equipment models and architectural / structural models
2. Copy important levels and acquire coordinates
3. Place the site logistics components on each level, as required
4. Hide linked models and export 4D site logistics model to desired format (DWF)
Add generalized crane rigging when lowering items from above
Add installation equipment that is required to move with the equipment during routing (e.g., sleds)
Adding geometry to represent accurate overall size of the equipment in the state it will be routed into place
1. Use the site logistics model as a starting point, if available
2. Insert on-site construction equipment to be used in routing
3. If adding rigging elements to an item, use an in-place model to generate a simplified version of the crane rigging as necessary to more completely represent the size of the routed equipment
Project Timeline Simulation
To achieve a project timeline simulation it may be necessary to use Revit to:
Break model elements into parts / pieces for simulation when it was modeled as a single item for 3D coordination purposes
Add data to model elements that correspond with project sequence task name
Add installation equipment (e.g., cranes, sleds, carts); also done in equipment routing
Add key milestone indicators to represent milestones that cannot otherwise be represented in the 3D model (i.e., site readiness requirements)
Revit family editing may be necessary to split objects that are not normally modeled in two pieces. At KONE, the best example of this is the escalator truss. The only extra geometry you may add using Revit are the key milestone indicators.
1. Working in a 4D template, use model text based component to add notes to the 4D model
2. Position the model text component outside of the building model in an easily viewed area from the standard isometric views
Navisworks is where all the coordination and simulation takes place. It is also important because of the integration with BIM 360 Glue. We have seen many projects use cloud-based coordination / model sharing tools and it saves us a lot of time in downloading and model updating. Regardless, the 4D tasks remain the same: extra models appended to the federated building information model whether that is local or through a central connected repository.
Site Logistics Model
The site logistics models should be a requirement of any practical 4D simulation to clarify site readiness. It is also foundational for computational space planning for construction, optimizing on-site construction traffic, and supply chain.
For now, the model is static. Nothing is animated but Navisworks is still the best place to view, comment, and coordinate the space needed for clear work areas, on-site material storage, and staging or delivery areas. Usually this helps us point out the need for multiple deliveries as well as the topic of project sequencing.
1. Export the site logistics model from Revit to a Navisworks format. This is a different model than your building geometry.
2. Append the site logistics model exported from Revit. We use DWF or IFC.
3. Isolate building floors with site logistics using sectioning tools.
4. Save Viewpoint(s).
5. If necessary, select the object and use the Item tools to Move, Rotate, or Scale.
6. Screen capture or export image formats.
Explicit 4D Simulation Versus a Construction Site Digital Twin
Most project simulation falls into the category of “Hollywood BIM.” It is interesting, and most people enjoy watching a 90-second animated video of their project, but it is for entertainment purposes only.
We can, however, implement 4D coordination and simulation on real projects in a practical way. We are usually doing this with a very specific purpose. If a question is asked and a simulation can help provide an answer, we simulate. We ask an explicit question and simulate to solve. For instance:
If a customer wants to see a high-level animation of equipment being installed, even though it might not be a hardcore preconstruction planning use case, it still is a question that we can help explain through a model and animation.
If a contractor is uncertain that we will be able to lower the escalator truss into place without needing to split the prefabricated truss, we can animate that.
If we need to test the size and movement constraints of material transportation systems, we can animate that.
If we are dealing with a very tight construction site, on-site material storage needs may be best communicated in a 3D model view. We can model that.
If we always apply 4D coordination in this way, we avoid the “purely for entertainment purposes” pitfalls of a lot of 4D being produced.
What Is a Construction Site Digital Twin?
On the other end of the spectrum is an overall digital representation of a construction site. Although the term 'digital twin' has many interpretations, digital twins of the construction site can be leveraged in the following two ways.
Preconstruction Simulation and Analysis
When the construction requirements for all trades can be represented digitally over time, there is an opportunity to plan the construction site computationally. Think of the generative / computational design tools available today applied to the shapes representing work areas, material storage, and egress areas during construction. The process could simulate iteratively showing the progress of different trades through the project and highlighting optimized adjacencies and overlap in similar logical engines.
Real-Time Digital Construction Site
Consider two characteristics of digital twin:
1. The digital representation must exist as a representative of a real object, serving as a container for information about actual live conditions, along with other static properties such as model number, etc.
2. The digital representation does not just receive information but also is able to act on the real equipment, changing its state. It can then be measured or validated through sensor feedback.
The digital twin is not just an accurate 3D representation of something real; it is alive with information and it changes with the real-world conditions over time. The goal of this type of digital twin for the construction site is to more easily consume large amounts of interconnected information about one or many assets. This could be useful to decision makers in order to better assess current conditions and make better future plans. The promise of sensor proliferation, reality capture, and AI object recognition gives us an answer as to what the future may hold for real-time construction site digital twins.
When you accurately simulate and use it as a planning tool during construction, 5D construction cost integration and supply management are near.
The Short Step to 5D
It could be argued that a 4D construction simulation cannot be complete without financially representing the work completed. In fact, the entire 4D simulation could be based on billing / payouts, or what is widely considered to be 5D construction cost integration.
In other words, by attaching models to specific payouts that happen over time (i.e., materials arrive on-site, machine room ready) or interdependent milestones to payouts (site readiness), then we are accomplishing a version of 5D, as a workflow of 4D. This would be most helpful for the owner, so that an easy comparison can be made with expected site conditions at specific payouts.
It is important to identify 5D not as a single solution, but as an explicit solution for the primary building stakeholders:
Designers 5D—Quantity-based counts for GMP study or validation
Builders 5D—Simulating payouts over time through a 4D simulation during planning that can be compared to real conditions during construction
Owners 5D—Lifecycle cost included as data in the model including regular maintenance costs, expected lifespan, and full replacement cost
If you coordinate in 3D today, consider adding key site logistics modeling and large equipment routing to the scope of BIM work on your project in order to improve construction site efficiency. This is incredibly important to the future advancement of BIM use, the smart construction site, and the needed step change improvement to construction productivity. Consider construction site modeling and 4D simulation as foundational to enabling prefabrication and the future robotic methods of delivery and construction.
Ken Flannigan is a technology leader who works with KONE to guide BIM processes and research globally. Ken believes that there are great industry challenges afoot as benefits of BIM have gone mostly unrealized and industry-wide productivity has remained flat. Ken has led technology implementation efforts including BIM automation of configure, price, quote systems, and integrating BIM-centric workflows on an local and global scale. Ken serves on the BIMForum LOD Specification Committee and is a LEED Accredited Professional.