The Swinerton Portland team recently embarked on procuring and erecting the largest Cross-Laminate Timber (CLT) project by square footage in the United States. The project is a 156,000-square-foot glulam Beam and CLT class A Office building with a steel brace frame lateral restraint system. Mass timber construction is beginning to turn developer’s heads in the mid-rise construction market, particularly for the creative office market sector.
CLT panels are created from a process of pressing and gluing two-foot by six-foot boards to make a structural floor or wall assembly. These boards are sandwiched in alternating, perpendicular layers that are three, five, seven, or nine layers thick. Manufacturing of the panels are limited to five North American fabricators and a handful of European fabricators. Timely fabrication and procurement of the structural system is critical to minimizing project risk.
The glulam beam-to-column connections are joined together using concealed connectors that allow the beams to slip into place on the columns with no on-site hardware installation, drilling, or cutting. The offsite fabrication of the glulam beams requires a longer procurement period; however, savings is realized onsite with labor and schedule benefits. The key to building with CLT and glulam Beams is to focus on procurement and supply chain management so that there is never a shortage of material onsite.
Traditionally, wood was used and implemented on projects as sticks of lumber. Prefabrication of the lumber was not seen as necessary or advantageous; however, the mass timber buildings that are being constructed today are utilizing fully-coordinated BIM models to treat the construction as prefabrication. As an example, Swinerton’s Oregon project had over 3,200 electrical penetrations drilled into the exposed CLT panels in the factory on a CNC machine. All trade partners and team members bought into this approach to save money and time and reduce the risk of potential quality and safety issues by not having the work performed in the field—ultimately creating a successful installation.
Additionally, the CLT erection on the project is being self-performed by a team of eight people. BIM coordination is utilized to track the placement and timing of installation. The team’s efficiency means it can erect a floor in four days (setting columns is one day, setting beams is another day, and placing the CLT deck is two days).