Colorado Real Estate Journal - December 16, 2015
Most architects and builders would agree that saving an outdated building from demolition and repurposing it for a new use is the most sustainable solution structurally, yet this approach isn’t considered often enough. Keeping the majority of an existing structure intact, along with all of its embodied energy, well-designed upgrades and additions can transform buildings into world-class facilities that offer greater flexibility for future needs. Reuse also can save the cost of demolition and substantially minimize the carbon footprint. As developers and owners consider tapping their existing building stock to expand their portfolios and minimize their carbon footprint, the structural engineering industry can help revitalize and adapt these buildings for uses never considered when they were first built. The approaches our firm has used to accomplish this on recent projects in Colorado successfully demonstrate that saving a building does not have to be overly expensive. Take the Lory Student Center (Phase II) on Colorado State University’s Fort Collins campus, for example. The original CSU Student Center designed by architect James Fisher, was a midcentury Bauhaus building completed in 1962 with clean lines, a regular grid and an open floor plan. As time passed, new building additions began to mask many of the building's good features, resulting in increasingly confused wayfinding and orientation for students. In 2010, the university hired design architect Perkins + Will, with ALM2 as the local architect of record, to address these issues and more. The architects envisioned preserving the integrity of the original design while expanding the center’s capacity to meet the needs of a growing campus. They concluded that by increasing the building’s size to grow student services, opening up views to the mountains to facilitate easier wayfinding and expanding the ballroom (the largest gathering space in Northern Colorado), a more welcoming, vibrant hub would drive increased student visits to the heart of the campus. Further, these upgrades would create one of the most sustainable student centers in the country. In addition to wayfinding issues, energy usage was challenged by the building's original 1960's mechanical systems, single-glass pane exterior envelope and minimally insulated walls. CSU's budget didn’t allow for wholesale demolition of the existing building and replacement with a new, larger building, so the architects turned to Studio NYL to come up with structural strategies that would help them achieve their goals. To support the architects’ ultimate vision we proposed using external FRP (fiber reinforced polymers) to enhance the original cast-in-place concrete flat plate floor slabs, while also checking the columns and upgrading the foundation for the increased loads. The FRP solution, which they chose to implement, solved two things simultaneously: • It upgraded the floor’s live- load capacity in lower-capacity areas so uses up to 100 pounds per square foot could be placed anywhere inside the building, allowing the university to have ultimate flexibility for the future; and • The FRP strengthening, bonded to the underside of the floor slabs, required only ¼-inch of space (unlike the more common solution – a 12-inch-deep fire-proofed steel beam grillage placed below the slab). Thus, with floor-to-ceiling heights of only 12 feet and ceiling heights at 10 feet, which is minimal for the uses proposed, this allowed for ample headroom throughout the building. One of the advantages of FRP systems (typically carbon, glass or aramid, with carbon being the strongest) is that they are easily applied by small crews of two to three people after lightly preparing and cleaning the existing concrete surface to remove laitance (a milky deposit or accumulation of fine particles on the surface of new cement or concrete). An epoxy bonding agent is then applied, onto which the FRP is adhered. On this project, a variety of FRP forms, which come in sheet wrap or narrow strips, were applied in various orientations, spacing and number of layers to match the given load demands in each area of the structure. The underside of the slabs were reinforced in the middle of the bays, while the top surface of the slabs were reinforced around the column locations. The engineers at Studio NYL liken it to applying “structural wallpaper” to increase the strength of a structure. An added benefit of using FRP systems on this project was the increased strengthening of the concrete floors along the structural column lines. This allowed large openings in the middle of the concrete floor’s structural bays to be saw-cut out and daylight to penetrate down through the building’s three levels. This activated the spaces architecturally, and increased the well-being of users on the bottom floor – previously known as the “dungeon.” This upgrade of the Student Center’s floor capacity using fiber-reinforced polymer (carbon, in this case) delivered multiple benefits. By reinforcing the floors, openings could be punched vertically through the structure to harvest daylight deep into the lower level for the first time in more than 50 years. This approach also provided greater flexibility and expanded uses for the university without compromising the building’s structural integrity. In addition, student well-being has increased, and the overall user experience transformed, as a result. FRP strengthening systems can be used on many materials, including concrete, masonry and timber. Studio NYL has proposed using these systems on a variety of renovation projects for a number of structural reasons, including increasing bending and shear capacity, confining column axial loads and enhancing lateral loads though shearwall upgrades, but our primary reason is to save the embodied energy already existing in the building’s structure. To this end, FRP systems were used at the original Walsenburg High School (built in 1911) to allow the main-level classrooms concrete floor to be transformed into the Spanish Peak Library, which required increased floor loading for library book stacks. FRP systems also were applied to the existing concrete shearwalls on CSU's Lory Theater (Phase 1 of the Student Center) to create a large window opening where daylight now penetrates into the university's new multifunction theater and banquet space.