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Over the past decade, Building Information Modeling (BIM) has almost entirely replaced the conventional 2D drawing method in large scale building structures design. Through 3D modeling and rendering, developers can get a virtual sense of the structures they propose long before they invest in construction, while architects and engineers are able to better convey their designs to contractors before they mobilize. While these benefits are useful in developing the facility during the design process, the primary benefit of BIM is collaboration and coordination between disciplines, especially through the often-underutilized tool of clash detection.

Clash Detection Benefits

Elements clash when they occupy the same space. Clash detection is an automated process that compares various BIM elements to determine and report any potential clashing constructability issues. The user chooses which element types they wish to compare, and the program will find and prepare a report of possible element clashes for the user to analyze. For example, if the mechanical engineer wishes to know if the optimal ductwork configuration conflicts with the structural bracing system, this process will identify and report the possible conflicts so that both the mechanical and structural designs can be revised to accommodate the needs of the facility as a whole. Compared to the outdated conventional process of each discipline reviewing their own design as best they can prior to construction and then resolving conflicts as they materialize in the field, BIM clash detection is a proactive measure that saves the designer and developer both time and resources. However, as powerful as this process is, it is by no means perfect.

Clash Detection Limitations As with all technology, the clash detection process is only as powerful as its user. Without the prerequisite knowledge as to why certain elements need to be placed where they are, the process of clash detection will not prioritize the clashing element or determine which element needs to be moved or to where. Furthermore, because of the current limitations of the software (or the amount of effort each designer has available to develop their BIM) not all building elements are modeled.

For example, while it is industry standard practice for the structural model to contain lateral bracing elements, because of the effort involved, it is not practical for the brace connections to be modeled. It is up to the user’s discretion to allocate space for these elements and alter their design accordingly. Because the clash detection is performed by computer, it also does not discriminate between meaningful clashes and those that can be ignored. Conduit that is nested inside of a partition wall is technically considered a clash by the computer but is standard building practice and easily achieved in the field. For many facility projects, this process can lead to over half of the reported clashes as meaningless. The limitations of clash detection can only be resolved through communication between trades.

Early Clash Detection As the time of this writing, communicating BIM clashes is the most tedious portion of the clash detection process. For large scale projects, the industry standard is for one or more parties to run clash detection, create a report, and then all disciplines collaborate to determine conflict resolution. Because of the monotony and effort involved, most design teams will make the mistake of running this process towards the end of the design phase. Delaying this process not only increases the effort of resolving each individual clash, it also increases the severity of each clash.

For example, moving a heavy piece of electrical equipment to avoid a clash with accessibility requirements at the early stages of design will allow the structural system supporting the heavy electrical equipment to be redesigned prior to the structural foundations design. This potentially saves the structural engineer time and effort of redesign due to circumstances of which they have no control. A proactive approach will not only reduce the number of clashes but will make the clashes that do occur more manageable. For this reason, it is advantageous for each discipline run their own clash detection periodically throughout the design process.

Clash detection technology has made great strides in becoming more user friendly. With the advent of customized searches, focused reporting, and greater detailed models, clash detection is easier to perform and more powerful than ever. The cost and resource savings of detecting clashes prior to construction make this service marketable adding value to design.

About Foresite Group

Foresite Group is a multidisciplinary engineering, planning, and consulting firm providing services to public and private sector clients nationwide. Our team’s collaborative process results in creative products and services that help our clients achieve their goals. Our team takes pride in enhancing and developing the cities and communities where we live, work, and raise our families.


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