Many factors affect a project’s construction timeline; the structure’s design, complexity, and location are all part of the equation. One of the most critical factors at play is the building material used, and in nearly every situation, leveraging precast concrete products leads to enhanced speed and efficiency. Such is the case in Cullowhee, N.C., where officials at Western Carolina University (WCU) decided on a total precast concrete solution for three new residential halls. Overcoming weather-related issues and delays arising from the COVID pandemic, the project, which was led by the PCI-Certified precast concrete producer Tindall Corporation of Spartanburg, S.C., leveraged an innovative precast concrete approach and the use of building information modeling (BIM) to successfully deliver a first-of-its-kind structure on time and within budget.
BIM + Precast Concrete = Success
With the school expanding at a rapid pace, WCU clearly needed additional housing. Therefore, WCU officials sought a building material that would not only be able to function for the long term but would also allow the work to be completed quickly. Constructing multifamily structures requires considerable coordination of mechanical, electrical, and plumbing (MEP) components to ensure a smooth build-out and comfort for those who will live, work, and play inside the building. To meet these needs, Tindall Corporation used an innovative prestressed floor slab system developed in Denmark. By casting electrical conduits and boxes into the floor and roof systems and providing options for attaching mechanical and plumbing components into the precast concrete slabs, the project team was able to compress the construction timeline, allowing interior work to proceed earlier than normal.
“Precast concrete allowed for the bulk of the MEP coordination to be completed during the engineering phase of the project,” said Donavon Burns, PE, lead engineer at Tindall Corporation. “It also provided the ability for openings, electrical components, and embeds to be cast in a controlled plant environment. With this floor system, once the slabs were set, the bottom of the surface was ready for paint, reducing the amount of drop ceilings required.”
The system is composed of lightweight concrete blocks that allowed crews to place prestressed reinforcement lengthwise and traditional reinforcement in the transverse direction before the blocks were encased with self-compacting concrete. In some locations, lightweight blocks were eliminated to offer flexibility for mechanical and plumbing penetrations. When compared with more-conventional construction methods, this system required increased collaboration and coordination on the front end, but it ultimately resulted in the trades being able to accelerate on-site work.
The team leveraged BIM heavily throughout the project, from initial design through production, shipping, and erection. During the design phase, BIM was vital for clash detection, locating electrical conduits and boxes, and determining mechanical and plumbing penetrations for casting into the precast concrete slabs. In the manufacturing phase, the BIM software generated code to guide the light-aggregate concrete block machine that was used during the production of each piece of the roof and floor slab system. This code helped control where blocks needed to be omitted from specific slabs to accommodate cast-in penetrations and electrical components. During the erection phase, the BIM software allowed the erector to quickly create an erection sequence by choosing pieces from a three-dimensional model and placing them in the desired successive order.
More than 200,000 ft² of the precast concrete floor system was installed on the project, and 215,000 ft² of precast concrete wall panels comprise the exterior of the new residence halls. These panels were manufactured with an architectural concrete mixture and sandblast finish.
“The wall panels were insulated to provide thermal efficiency, requiring fewer furred out walls for the contractor to construct in the field,” Burns said. “Panels were poured with an architectural precast concrete wythe and set in the field with a finished surface, eliminating the need for paint or a wrap.”
Because the team used a total precast concrete structure and leveraged the power of BIM, the resident housing, which will benefit WCU students for years to come, was constructed over the course of just eight weeks.
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013.