Scheduling and the 4th Dimension
Scheduling logic can be augmented by the increased visualization that BIM brings to a project. Project teams not only have the ability to view 3D space with BIM, but also have the opportunity to view how their logic looks when simulated with BIM. This enhanced simulation gives feedback that allows team members to adjust their logic to best fit the project’s construction sequence.
Meeting with the project team
Before a project enters into the 4th dimension, it is necessary for the project team to meet with the BIM team to establish the intent of the schedule simulation. Crucial elements such as scaffolding are rarely modeled by detailers, but are necessary for a construction simulation. Once all elements necessary for a full simulation are established, the simulation can be created.
Early Use of the Model
From the beginning of a lean scheduling meeting, BIM can be used to assist the planning session. Geometric relationships can be shown to the project team to further their understanding and to help the team determine the best order of installation. To enhance understanding, visualization techniques such as color coding systems and areas can be used. For example, priority walls could be colored orange and non-priority walls could be colored white. This helps the entire team know where critical areas are located and allow them to better determine how construction will occur.
Figure 1: Lean scheduling meeting
Importing the Schedule
After a lean planning session, the schedule is released to the masses and can be brought into Autodesk® Navisworks® for enhanced analysis. To bring a schedule into Navisworks, open Timeliner Home>Tools>TimeLiner. Select the Data Sources tab and select the Add button. The button reveals a drop-down of data sources that allows you to choose from a number of popular scheduling programs. If the software you use is not included in the list, you can always import a csv format to connect to the schedule. Once you select your link, you will have to map the information with the Field Selector. This form connects the fields from the selected source with Navisworks. If at any time in the future you need to change the mapping, simply right-click the link and select edit.
Figure 2: Adding schedule
Once the link has been created, you can build a link into Navisworks. Right-click the link and select Rebuild Task Hierarchy from link or select the Refresh button. This builds all the items from the schedule into tasks. If at any time the schedule is updated in the authoring software, you can update your tasks by right clicking the link and selecting synchronize or by pressing the Refresh button.
Figure 3: Clash batches
Tasks from the schedule now appear in the task tab of Timeliner. If there are tasks not shown in the schedule, but are part of the simulation you wish to show, you can add them. Right-click and select Insert New Task. Change the planned start and planned end time accordingly.
Connecting the Model to the Schedule
After tasks have been created, it is possible to connect the model to the schedule. There are two ways that this can be accomplished: statically and dynamically.
To attach model component(s) to a task statically, identify the task you wish to connect to the model. Select the object(s) in the model you wish to attribute to the task, right-click the task, and select attach current selection. Selection sets and search sets can also be attached in like manner.
To attach model component(s) to a task dynamically requires special naming conventions and rules. Each task generated from a link has a unique ID. This ID is perfect for setting up a dynamic relationship with the model. To do this, create search sets to find the model components you wish to add to a task. Name the search set the same name as the unique ID of the task. For example, installation of solid core doors on level one has the ID L1a-1001. A search set of all the solid core doors would be made and named L1a-3001. This connection is dynamic in two ways. First, if the model changes, the search set changes with it. Second, if the schedule changes or is even deleted, it can be brought in without having to reform links. If you create selection sets instead of search sets, the connection to the schedule is still dynamic in the sense that the link can be deleted and re-connected; however, if the model changes, the selection set by nature will not change with it.
The second step in connecting the model to the schedule involves the creation of rules. Rules are created by pressing the Rules button on the Tasks tab of Timeliner. Create a new rule and change the rule to align with Figure 4 below. This rule connects the external ID from the link to the selection set with the same name. Make sure the checkbox for this rule is selected and press Apply. After you apply this rule, all the sets you created will attach themselves to your tasks.
Figure 4: Dynamic rules
Configuring the Construction Sequence
The model should now be attached to the schedule; unfortunately, this does not mean that the model will build itself when the simulation is run. This is because each task must have a type defined. The typical types are Construct, Temporary, and Demolish. When a task type is set to Construct, the objects associated with that task will show for the first time semi-transparent as soon as the simulation hits the start date of the task. When the simulation hits the end date of the task the objects will appear completely. Demolish works the opposite way. At the beginning of the project the objects appear completely. When the simulation hits the demolition date the objects become semi-transparent, and when the simulation hits the end date the objects disappear. The Temporary task type works between the two, coming in transparent at the start and disappearing at the end of its scheduled dates.
Navisworks allows you to customize these settings. You can change the colors and transparencies of these task types and even create your own. For instance, you might set up special rules to show the construction of phase 1 and all of its associated items one way, and phase 2 another. This customization allows an added layer of analysis for your scheduling review.
To create a custom rule simply select the Configure tab and press the Add button. Configure the color and appearances according to your analysis needs.
Figure 5: Configuring task types
Running the Simulation
Once the model has been connected to the schedule and had its task type defined, the simulation can be run. Often, it becomes useful for teams to change the start or stop date. To change these dates press the setting button on the simulate tab.
At any time during the simulation you can pause the simulation and walk around the model to see what different activities are being performed at any given location in the model. Not only can you see what systems are being installed, but also what percentage each system installation is at through use of the Gant chart.
The simulation can be exported as a video. Individual pictures can also be exported to clarify installation of specific areas at specific times. This tool enhances visualization and brings the team into the 4th dimension.
After construction begins and the schedule is updated, Timeliner allows tracking of changes between actual and planned. Color differences appear where the schedule deviates,
Figure 6: The 4th Dimension
Managing the 4d Workflow
A lot of up-front work is done by the team to create a dynamic link between the schedule and the model. This work can be reduced if a company has defined naming conventions. In the scenario listed above, the unique ID could be defined in advance. For instance, all interior doors on a level could be named LVX-aX003 where X is the level number. If naming is standardized in the schedule, standard search sets can be created that can be used over and over on projects by utilizing the power of xml. A search set can be exported as xml and then imported into another project. This can take much of the up-front work out of the 4th dimension process.
It is important for a team to recognize the importance of the dynamic environment. Models do change during design and construction. The schedule also changes, but the unique IDs do not typically vary within the same project. Some IDs may be added which may require a new model connection, but deleted items don’t require model maintenance. Scheduling items that change their start and end dates also do not require model maintenance in a dynamic environment.
Michael N. Smith is a BIM Manager for C.W. Driver, a large general contractor in Southern California. The firm is highly regarded throughout the design and construction industry for implementation of BIM innovations on each project, and for creating customized software plug-ins to increase the efficiency of the latest software releases. Michael is also a guest author and technical editor of Mastering Navisworks 2012. He can be reached at firstname.lastname@example.org