In this module, I would like to introduce BIM application on construction progress management, called 4D BIM. Let us first define what 4D model and 4D simulation are. A 4D model comes from a 3D model linked with project schedule, the fourth dimension: time. A 4D model shows the changes of both geometric and non-geometric information within the lifecycle of the model. Traditionally, a 3D CAD model is used and geometric CAD entities need to be grouped together as building objects or components first, before they can be linked to corresponding schedule items. Nowadays, a 3D BIM model can be used and existing building objects in it can be more easily linked to project schedule items. A 4D simulation is a process that controls and arranges the construction tasks based on 4D models. A 4D simulation may look like this. In the simulation, as the time goes, the statuses of the construction project at specific times are animated with objects in different colors to indicate their different construction statuses. For example, we may use five different colors to indicate different construction statuses. In the case shown, within a period of time for 4D simulation, if construction of the objects is completed before the period of the time, the objects are colored in pink. If the objects are under construction, we color them red. If construction of the objects is just finished, we color them yellow. If construction of the objects are completed with the period of time, we color them blue. If construction of the objects has not been started yet, the objects are colored in orange. To produce good visual effect of 4D simulation, careful selection and assignment of colors for different statuses is needed if the software does not provide good enough default settings. 4D simulation is very helpful for project management. Through a 4D simulation, all activities in the construction process, especially those important or critical ones, can be visualized in a more straightforward way. This helps us identify conflicts, errors, and problems in a virtual environment before actual construction, so we can resolve them in advance. It is obvious to see the benefits of 4D simulation to coordination, collaboration and integration among stakeholders as well as resource management of the construction project. Many software vendors have provided software functions for 4D simulation. In this course, we introduce Navisworks to let you get some experiences on preparing and executing 4D simulation. In preparing a 4D BIM simulation, besides the 3D BIM model with sufficient building objects and a schedule with concerned activities in a period of construction process, the key task is on binding together the corresponding model objects and schedule activities. This task can be tedious and very time consuming, therefore, we may need to device some strategy and take advantage of the functions and tools provided by the software to simplify and automate the task as much as possible. We will discuss this further in later hands-on sessions. 4D simulation can also be used to review the sequence of construction activities. In this case, pseudo time, instead of real time, is used for the fourth dimension because the relative sequence of activities is more important than the real times for the activities to take place. Furthermore, 4D simulation is often used to review critical crane operations in construction, especially when multiple cranes are involved.
