In this lesson, students explore how to use 4D simulation to support construction planning and assess the impact of proposed design features on the construction schedule and workflow. This feedback provides valuable information to inform decisions as project teams evaluate and assess potential design features and construction options.
Students will learn how to use a workflow combining models created with the Autodesk Revit platform with the Autodesk Navisworks® TimeLiner tool to create 4D simulations of planned construction processes. They will explore modeling techniques for creating better and more accurate simulations, as well as the importance of modeling building elements to reflect planned construction techniques. They will also learn to use Revit features, such as project and shared parameters, to add information to building model elements that supports additional uses of the data in the building model—in this case, for materials tracking and management.
Applications of BIM Models for Construction Process Planning
Using the Autodesk Revit platform in combination with Autodesk Navisworks Manage creates a workflow that enables project teams to effectively plan construction operations, identify potential problems, and explore and evaluate alternatives. Using these tools, construction planners can simulate planned sequences of construction activities, identify clashes and interference problems, find opportunities for improving construction schedules, track materials and manage the supply chain, and much more.
Some suggested applications of BIM for construction planning include:
- 4D Modeling—simulating the planning sequence of construction activities and space requirements on a building site.
4D modeling provides a powerful visualization and communication tool that gives project teams (including owners and building users) a better understanding of project milestones and construction plans. 4D simulation can help teams identify problems well in advance of construction activities, when they are much easier and less costly to resolve.
4D models can also used to plan the phased occupancy in a renovation, retrofit, addition. Creating dynamic phasing plans of occupancy enables multiple options and solutions to space conflicts to be considered and evaluated.
Site Utilization Planning—using BIM models to evaluate the locations of both permanent and temporary facilities on site during multiple phases of the construction process.
BIM models can be linked with construction activity schedules to explore space and sequencing requirements. Additional information describing equipment locations and materials staging areas can be integrated into the project model to facilitate and support site management decisions, enabling project teams to effectively generate and evaluate layouts for temporary facilities, assembly areas, and material deliveries for all phases of construction
3D Coordination and Clash Detection—identifying potential conflicts by comparing 3D models of all building systems.
The goal of clash detection is to reduce and eliminate field conflicts, which in turn reduces RFI's, reduces construction cost, and increases productivity on site.
Identifying Time-Based Clashes—verifying the planned sequence of construction operations on constrained sites to confirm that the demolition, permanent construction, and temporary construction activities can occur without creating conflicts.
Time-based clash testing provides valuable insights for construction planners as they coordinate the trades, materials, and equipment that must coexist in the limited space available. Construction planning models can be integrated with the composite project model and linked to the project timeline to consider the impact of temporary items (such as work packages, formwork, cranes, installations, and so on) and check for potential time-based clashes.
Construction System Design (Virtual Mockups)—creating a model to design and analyze the construction of a complex building system (for example, formwork, glazing, tie-backs, and so on) to support detailed construction planning.
Creating virtual mockups of a construction system design can increase the constructability of a complex building system and construction productivity on site by effectively planning and communicating the complexities of the process to all participants.
Materials Planning and Management—using 4D modeling and links between the building elements in the project model and the associated task schedule to forecast the dates when elements are needed on site for installation.
Parameters can be added to the elements in the project model to track their ordering and delivery status and manage the supply chain for materials needed on site.
Creating 4D Simulations
By linking timelines of project tasks to model elements, we can create a complete 4D simulation of the construction process from the demolition phase through owner move-in. This simulation can be used to inform critical planning decisions about construction methods, resource allocation, activity sequencing, site space utilization, and so on.
Using the Navisworks® TimeLiner tool, project teams can simulate construction processes by:
- Manually enter information about project tasks or import schedules from many project planning software applications.
- Link elements in the composite model with tasks in the schedule.
- Simulate the schedule and viewing the effects on the model, including planned versus actual schedules.
To simplify this process on large and complex projects, it is common to include key building elements in the 4D simulation and omit less important features. The primary elements that are typically required in 4D simulations include:
- Structural system—structural framing components including foundations, grade beams, columns, load bearing walls, floor and roof decks and support.
- Exterior building envelope—stud wall, exterior panels and assemblies, curtain walls, openings, and glazing.
- Interior partitions—main interior walls, plumbing walls, and wall assemblies.
- Mechanical systems—main ductwork and equipment, separated by floors.
- Roof systems—roof assemblies, major equipment, and openings.
- Site work—excavation work, footings, foundations, and slabs on grade.
- Plumbing systems—main connection lines from site and main plumbing lines.
Maximizing the Effectiveness and Value of 4D Simulations
In order to create accurate and truly useful 4D simulations, it is critical that building elements be model in a way that mirrors the actual construction process planned. Strategies for doing this include:
Using Parts to Schedule the Layers of an Element Independently
Building elements with structures composed of multiple layers that will be installed at different times (e.g. the core structural layers of a wall assembly versus the interior and exterior finish layers) should be decomposed into parts to allow accurate scheduling of individual layers.
Scheduling the original multi-layer element can create simulation errors (interior and exterior finishes being installed at the same time as the structural core), and this inaccuracy diminishes the value of the simulation for detailed construction planning.
Splitting Larger Elements to Model Location-Based Scheduling
Large, continuous building elements that will be installed in smaller pieces (e.g. long wall sections that span the entire face of the building) should be split into segments that match the actual construction process.
Creating overly lengthy tasks to match the building elements builds artificial delays into the simulation and diminishes its value as a planning tool. It is better practice to subdivide the elements into realistic chunks that match actual construction activities.
This approach is commonly used to support location-based scheduling—a strategy that attempts to create smooth, parallel workflows of sequential construction tasks through project locations by adapting the work crews and planned activities to minimize conflicts and delays created by location unavailability.
Advantages of 4D simulation
The ability to forecast and anticipate problems before they occur is essential for effective project management. When the cost of schedule delays or construction rework because of errors is considered, it is clear that project managers need to carefully plan and orchestrate construction operations down to the last detail, both in space and time.
Traditional scheduling methods do not address the spatial aspect to the construction activities nor are they directly linked to a design or building model. Traditional bar charts or Critical Path Method network diagrams can be difficult to understand or interpret. Having the ability to watch the elements of a design come together onscreen gives the design and construction team improved accuracy in construction sequencing.
4D simulation enables project teams to:
- Inform design decisions by considering the impact on construction of proposed design features.
- Identifying and resolving problems earlier (when needed changes are easier and less costly to implement).
- Assess and manage project risks.
- Improve project schedules and bring facilities online sooner, which is typically a great benefit to the owner and users.
After completing this lesson, students will be able to:
- Understand how to use 4D simulations for construction planning.
- Appreciate the importance of accurately modeling building elements to improve construction simulations.
- Identify and explore opportunities to reduce delays improve construction plans using location-based scheduling strategies.
- Utilize and leverage project and shared parameters to track the status of building elements and identify materials availability problems.
Improving Models to Enhance 4D Simulations for Construction Planning
In this exercise, students will learn how to:
- Use the Navisworks Timeliner tool to create 4D simulations of planned construction sequences.
- Link a schedule file to the TimeLiner tool and generate the hierarchy of tasks.
- Create selection sets and search sets to facilitate linking model elements to the schedule tasks.
- Specify simulation settings and run 4D simulations.
- Identify inaccuracies in simulations based on element modeling techniques.
- Divide elements and use parts to improve construction simulations.
Figure 7.2.1. Linking tasks to building model elements
- Create a 4D simulation of the construction process for the building in the exercise dataset.
- Use the construction milestone schedule provided in the dataset to create tasks for the planned sequence of activities.
- Create search and selection sets to link model elements to the construction schedule.
- Run the 4D simulation and save the results as a movie.
- Review the 4D simulation and note the operations that are not be represented accurately:
- Elements being constructed at the wrong time.
- Elements that are grouped that would actually be constructed in separate operations.
- Devise a strategy for reorganizing and dividing the elements to facilitate more accurate simulation of the construction process.
- Return to the Revit model and adjust the building elements to more accurately reflect the planned construction sequence. Adjust the:
- Column and wall top and bottom constraints.
- Wall heights and segmentation.
- Floor and slab divisions.
- Divide multi-layer elements into parts in order to simulate construction of the individual layers at the appropriate times. Create parts for:
- Multi-layer wall elements
- Multi-layer floor elements
- Multi-layer roof elements
- Export the improved construction model to Navisworks and adjust the tasks and selection sets to create a more accurate 4D simulation of the construction process using these parts.
- Run the 4D simulation and note the aspects that need further improvement to accurately model the sequence of construction operations.
Figure 7.2.2. 4D simulation using parts to accurately simulate the construction of multi-layer elements
Segmenting Elements to Model Location-Based Task Scheduling
In this exercise, you will learn how to:
- Use 4D simulations to identify opportunities for improving construction plans.
- Divide building elements into segments to enhance construction workflows.
- Reduce delays and improve construction schedules using location-based, parallel task scheduling strategies.
Figure 7.2.3. Assigning building elements to work areas
- Run the 4D simulation created in the previous exercise and look for items that are delayed, waiting for previous tasks to be completed.
- Devise a strategy for using location-based, parallel tasks to subdivide long tasks and shorten the project schedule by improving workflows. Consider the:
- Assignment of building elements to work areas.
- Column and wall top and bottom constraints.
- Wall segmentation.
- Floor and slab divisions.
- Return to the Revit model and adjust or divide the building elements as needed to model this new construction sequence.
- Export the new construction model to Navisworks and create a new 4D simulation of the revised construction process using the location-based scheduling strategy.
- Run the 4D simulation and note potential opportunities for further improvements to the planned sequence of construction operations.
Figure 7.2.4. 4D simulation of a construction plan using location-based, parallel tasks to improve the project schedule
Using 4D Simulations for Materials Planning and Management
In this exercise, students will learn how to:
- Add shared and project parameters to a construction model to track the status of building elements.
- Create schedules in Revit for planning and managing materials acquisition.
- Use 4D simulation to identify materials availability problems.
- Adjust construction plans and sequences based on materials availability.
Figure 7.2.5. Using parameters to track element availability in a Revit project model
- Run a 4D simulation on the model file contained in the dataset to identify the construction tasks planned for a specific time period – for example, week 11 of the project schedule.
- Create a search filter to isolate the building elements required for this set of tasks.
- Refine the search filter and viewpoint settings to highlight these elements based upon their availability – green for elements that are available, and red for elements that are not available.
- Identify the building elements that are not available and require expediting to allow construction as planned.
Figure 7.2.6. Viewpoint highlighting building elements based on their availability
- What is the advantage of using search sets versus selection sets for selecting model elements in Navisworks Manage?
As model elements are changed, search sets dynamically update to select all of the model elements that meet the search criteria. Selection sets are static. Once defined, they do not change automatically. So, as new elements are added to a model, you must adjust the selection sets manually.
- What is the advantage of adding task IDs to building elements in Revit to manage schedule linking?
Adding task IDs to building elements a Revit model makes it easy to automatically link those elements to construction tasks. By defining search sets that select model elements based on these task IDs, you can quickly select the elements related to a specific task and link them to the project timeline. This approach is much quicker and easer than defining search sets in Navisworks Manage based on element properties, such as name or type. You can use the powerful selection features available in Revit (for example, drag selection, filtering by category, select all instances, and custom search filters) to easily select groups of elements, then control the task linking by editing the values of the task ID parameter.
- How can construction planners use parts to improve construction simulations?
By breaking multi-layer building elements into parts, construction planners can create more accurate simulations of planned construction operations. For example, they individual layers and materials of a multi-layer wall are typically installed at different times—first, the structural core layers, followed by the exterior cladding and weatherproofing layers, and finally the interior finish layers after the building is weathertight. Breaking the wall into parts enables the different layers to be assigned to the right craft crews and scheduled at the appropriate time in the project timeline. While the modeling efficiency of creating multi-layer elements benefits the design process, from a construction modeling perspective, these layers should be separated and worked with independently.
- How do location-based workflows improve construction schedules?
Location-based workflows divide large schedule tasks in smaller ones, based on the work area in which they will be performed. These smaller tasks can typically be sequenced into parallel workflows that greatly reduce the delays of waiting for large tasks to be completed sequentially. Using location-based scheduling, construction planners can optimize and balance crew sizes to create smooth flows of tasks, constrained primarily by the availability of the work areas. And reduction of the delays between individual tasks, typically yields big savings in the overall project schedule?
Activities that appear in the project schedule. These activities can include construction, demolition, or temporary operations.
A simulation of a construction process that maps model elements to schedule tasks, adding the fourth dimension of time to a 3D model.
Planning and sequencing construction activities to optimize the flow of work crews and resources through various construction locations and minimize delays created by waiting for a work area to become available.
The process of planning, ordering, tracking, checking-in, and inventorying the materials needed to support construction operations. Materials management is critical to ensure that planned tasks are not delayed due to materials unavailability.