BIM is playing an ever-increasing role in complex construction projects and is now an expected part of preconstruction activities for many projects in every market. While typically used for clash detection, planning, scheduling, and cost estimation, it is the virtual modeling that changed the direction of an entire project.
The Challenge
Originally constructed in 1962, the United States Air Force Academy Cadet Chapel is currently undergoing a renovation to restore the most visited manmade tourist attraction in Colorado. Tasked with restoring a National Historic Landmark that comes with unconventional components as well as the geographic challenges the mountains bring, the JE Dunn team had to come up with a solution to keep work moving through various weather challenges including rain, snow, and high winds.
Because the scope involves removing all exterior metal skin, glass, and windows, the building interior will be exposed to the elements. This causes concerns not only for the work to be performed, but also for the products that have temperature limitations. As such, the team had to come up with a solution to ensure weather would not affect the ability to complete the work or the overall quality of the work.
The Solution
The original design documents for this renovation called for a commercial-type roofing system and special raised floor to redirect water to temporary gutters when it rains or snows. This would create a protective measure for the building interior but would not allow work to actively progress during these weather events. To solve both, the team came up with another conceptโa โcocoonโ that would enclose the entire chapel. By conยญstructing a building over the Chapel, workers can remain dry and safe on the inside despite the weather conditions outside.
One other positive outcome of the cocoon will be to provide an opportunity for a more robust hoisting system. Because of the geometry of the Chapel as well as its location being surrounded by retaining walls, the ability for cranes to both access the high points as well as lift material in high winds was also a concern. By designing an overhead bridge crane system to be integrated into the under-side of the cocoon roof structure, yet another potential problem was solved.
Due to the unique procurement method of this project, JE Dunn was provided the opportunity to present this concept to the Air Force Civil Engineering Center (AFCEC) prior to project bid. JE Dunn utilized their VDC Group to develop renderings which visually communicated the intent of the cocoon, as well as helped to show the interface of other complicated construction systems such as aerial lifts and complex scaffolding.
The Implementation
With such a unique enclosure, the building model played a key role in early decisions on design, construction, erection sequencing, and interface with other components of the project. The original structural design of the enclosure included cable stays anchored to the roof trusses, which were splayed and attached to the ground via soil anchors for stability. However, as the team was developing design of the enclosure utilizing BIM, in conjunction with the structural engineer (Bob D Campbell), they quickly realized that the cable anchors would be structurally inadequate and would also provide potential safety concerns for USAFA Cadets and the public. Based on these findings, the design was amended to provide robust steel kickers to strengthen the building, increase the factor of safety, and ensure the entirety of the enclosure supports remained within the confines of the project fence to limit potential safety concerns.
In addition to the enclosure itself, BIM also allowed the construction team to communicate with the government regarding crane placeยญments to provide a visual of what to expect, ensuring they were able to gain the acceptance from the Academy.
Lastly, the space between the exterior of the Chapel and the parapet of the existing retaining walls is very minimal. Despite this, large 185โ aerial lifts are required to access along the plaza to provide personnel access to the highest points of the Chapel. While these lifts are able to drive in a straight line across the plaza, the bodies of the crane pose a collision risk with the retaining walls when rotating to access the Chapel itself. By gathering BIM information from JLG, the lift manufacturer, JE Dunn was able to show these plaza areas, with the model of the actual lifts to be used, to ensure the body of the lift would clear the retaining wall without causing damage to the existing historical fabric.
The Results
Many projects leverage BIM for clash detection of complex MEP systems, but this particular renovation does not have much of that work type, with the primary purpose being skin-related. However, the early impact of BIM and JE Dunnโs VDC efforts will be felt in the years to come during this historic renovation.
While the accuracy of the virtual model aided in the construction of the enclosure, it was the ability to communicate visually with the owner and trade partners during the project planning stages that was the true game-changer. Without specifications or previous documentation of an enclosure of this kind, the model clearly showed the owner what to expect and relayed to the trades the type of environment they could expect to work in.
