In this session, we are going to use the “Interference Check” tool for clash detection. As we have already demonstrated interior and exterior decoration in the previous module, let us use it as an example to explain why do we need clash detection. In the real world, unless we pay attention to the relative sizes between the equipment and the space for placing them, we may sometimes accidentally place equipment that is oversized while making the design plans. For example, we may discover at some stage of design or construction that an oversized bathtub cannot fit into a bathroom with limited space. In this case, the wall and the bathtub are overlapping; this is what we call “interference” or “clash.” In construction engineering, interferences that are missed during the design phase are often uncovered during the construction phase, which requires changes in design, resulting in delays in construction. In Revit, we can fully make use of its “Interference Check” tool to detect clashes. Let us assume that each MEP design team has completed its own MEP models based on the completed architectural design. We need to make sure that there are no clashes among all designs from different design teams. To introduce how we can use Revit to achieve this, let us explain how Revit links existing models first. Let us create a Revit project file. Select “Mechanical Template,” then under the “Insert” tab, select the “Link Revit” tool. The pop-up window allows us to select a Revit project file. Let us select the file called “302_architecture.rvt" which contains a simplified architectural model provided for you. In the “Positioning” drop-down menu, remember to select “Auto – Origin to Origin.” Click on “OK.” Now we can see that the model we are trying to link successfully appear on the screen, but what’s different from our previous experience is that the linked model can be treated as an individual, grouped object, which means you cannot select any single elements like beams, columns, and walls within the object. But for using the model as a reference for the subsequent design requirements, it is more than enough to be able to see the reference model. MEP design teams only need to know where their equipment is fitted, and which walls the connecting piping should follow. So, once the architectural model is linked, they can design mechanical equipment and corresponding piping or other MEP systems in the project. We can also use the “Manage Links” tool to view all models linked to the project and link more models into the project. In this operating mode, we can click on the “Add” button to link more models. The “Unload” button can temporarily unlink the linked model to make it invisible; it can be reloaded when needed. The “Remove” button, on the other hand, can permanently delete model links. Here, we provide two sample files for practicing linking and clash detection: “302_watersupply.rvt” and “302_drainage.rvt.” These two files represent part of the water supply and drainage systems. Next, let us play the role of the designer of the water supply system. Open the file of “302_watersupply.rvt,” then use either the “Link Revit” tool or the “Manage Links” tool to link the drainage system model. Its filename is “302_drainage.rvt.” Please note, both the water supply system and the drainage system have been pre-linked to the sample building model “302_architecture.rvt” because they are designed based on the completed architectural model. When we attempt to link the water supply system model to the drainage system model, we can see a notification message stating: “The following nested links will not appear….” This is because the drainage system itself carries links. Links within links are referred to as nested links. But Revit sets a default linking mode called “Overlay,” which automatically gets rid of the nested links; this is exactly what we want because the water supply and drainage systems both link to the same architectural model and we do not wish it to be double linked. Once the drainage system model is linked to the water supply system project, let us check if there are interferences between the two systems. Due to the complexity of piping, using our eyes to identify all interferences is very difficult. So let us use the “Interference Check” tool to automatically complete the task. Under the “Collaborate” tab, on the “Coordinate” panel, click on the “Interference Check” tool. In the drop-down menu, select “Run Interference Check.” In the pop-up window, choose “Current Project” in the left-hand side “Categories from” drop-down menu. Then in the right-hand side “Categories from” drop-down menu, select the drainage system model “302_drainage.rvt.” For a simple demonstration, we only perform interference check for the pipes, therefore we tick “Pipes” for both sides and then click on “OK.” Then an “Interference Report” window will pop-up. Below the “Interference Report,” there are two essential functions: “Show” and “Export.” The “Show” function takes us to the locations of the interferences with zoom-in views. The “Export” function let us export the entire interference report as an HTML file, which can be opened by MS Word or internet browsers. For example, the drainage pipe and the water supply pipe have interfered in three locations. Let us choose the first case and select “Show;” Revit will highlight the elements that are interfering with each other. We can see that, in the piping closet, a horizontal water supply pipe interferes with a vertical drainage pipe. If the designer of the water supply system has known that the drainage pipe already occupies that space, he or she would consider moving the water supply pipe to avoid interference. From the above operational and simulating process, we can understand that the technique of model linking in Revit is essential; this is because every person in the cooperating team is developing and changing their models at all times. If they could continuously update their models and provide the information to the other team members through model-linking, any changes would immediately be displayed. After all the models are designed and adjusted, we would like to demonstrate how to merge the models into one single project file, instead of linking the models. Up to this point, we have linked “302_drainage.rvt” and “302_architecture.rvt” within “302_watersupply.rvt.” Because the linked drainage system model is treated as a grouped object, if we select it, the whole linked model will be highlighted. Under the “Modify | RVT Links” tab, on the “Links” panel, we can click on the “Bind Link” option to convert all the drainage pipes in 302_drainage.rvt into grouped elements in the project of “302_watersupply.rvt” and the drainage system model no longer appears in the linking list. But after binding the link, we need to remember to ungroup the elements. Click on the model, then in “Modify | Model Groups” tab, on the “Group” panel, select “Ungroup” because before this is done, the pipelines are considered a singular group of elements. Once we ungroup it, we can select and adjust each individual element.
