Structurally sustainable ways to transform existing buildings: CSU Lory
What is the most sustainable way to renovate existing buildings? Keep most of the existing structure and all of its embodied energy and upgrade and add onto the building. Upgrade the building structure’s floor capacity to provide flexibility for all of its possible future needs. Harvest daylight deep into the existing building where it was never experienced before to transform the users’ experiences and increase their well-being.
Studio NYL explains how they achieved this at the Lory Student Center on Colorado State University’s Fort Collins, CO campus.
Photo courtesy of Colorado State University. The Lory Student Center in 1981
Photo courtesy of Colorado State University. The Lory Student Center in 2019 following a 160,000 square foot renovation and 40,000 square foot addition.
The original 1962 building, designed by Architect James Fisher, was the new student hub of the campus, a mid-century building with clean lines, regular grid and open floor plans. Over the decades building additions had masked many of these features and wayfinding and orientation for students was confusing. Perkins + Will as the design Architect, with ALM2 as the local Architect of Record, envisioned preserving the integrity of the original design while expanding its capacity on the growing campus. The Student Center’s goals were to provide a more welcoming building and drive more student visits to the new vibrant hub at the center of campus, increase building size to add more student services, open up views to the mountains to assist in easier wayfinding, expand the ballroom (the largest gathering space in Northern Colorado) and upgrade the building to be one of the most sustainable student centers in the country.
Many strategies were required to achieve these goals. The energy usage was challenged by building mechanical systems that were still original from the 1960s as well as by single glass pane exterior envelope and minimally-insulated walls. Upgrades to all of those systems to state of the art practices, plus the addition of large PV roof arrays, meant that ‘the new building, even though 50,000 sf larger than the original 300,000sf building now uses less energy,” according to Mike Ellis, Lory Student Center’s Executive Director.
The structural challenge was that the budget didn’t allow for wholesale demolition of the existing building, replacement of it with a new, larger building to allow CSU to provide the increased services it wanted to give the student population. Studio NYL suggested 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 solved two things simultaneously: It upgraded the floor’s live load capacity in lower capacity areas, so the University would have ultimate flexibility of spaces for the future – any building use could be placed anywhere inside the building. Secondly the FRP strengthening bonded to the underside of the floor slabs took up only ¼” of space (unlike a typical 12” deep fire-proofed steel beam grillage below the slab, as is traditionally used), so headroom throughout the building was not compromised as the floor to floor heights were only 12’ and ceiling heights only 10’ typically, minimal per the Architects for the uses required and proposed around the building.
The FRP systems are easily applied by small crews of 2-3 people after lightly preparing and cleaning the existing concrete surface to remove concrete laitance. An epoxy bonding agent is then applied that the FRP (an epoxy polymer matrix reinforced with carbon fibers was used at CSU) is laid into. FRP comes in sheet wrap or narrow strip forms and a variety were used on this project in various orientations, spacing, and number of layers to suite the given load demands in each area of the structure. The underside of the slabs were reinforced in the middle of the bays, the top side of the slabs were reinforced around the column locations where the slabs go into negative bending. Studio NYL likens it to applying “structural wallpaper” to strengthen structures.
The other benefit of using FRP systems was it provided strengthening of the concrete floors along the structural column lines that allowed large openings in the middle of the structural bays of the concrete floors to be removed. This meant that daylight could penetrate down through the building’s three levels and be harvested at the lowest level, areas that had never before had daylight. This activated the spaces architecturally and increased the well-being of the users in the level previously known as the “dungeon”.
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FRP strengthening systems can be used on many materials such as concrete, masonry and timber. Studio NYL has proposed using these systems on a variety of renovation projects for a variety of structural reasons (increasing bending and shear capacity, confining column axial loads, enhancing lateral loads though shearwall upgrades), but in all cases it is to save the embodied energy already existing in the building structure. Studio NYL used FRP systems at the 1911 Walsenburg High School to transform the concrete floor at the main level classrooms into the Spanish Peak Library (with an increased floor loading for library book stacks). Studio NYL also used FRP systems on the existing concrete shearwalls at CSU Lory’s Theater (Phase 1 of the Student Center project above) to create a large window opening to allow daylight into the new multi-function theatre/banqueting space.
As energy use becomes more important and developers and owners look to their existing building stock the structural engineering industry can help revitalize these buildings and adapt them for new or alternate uses, many not perceived when the buildings were originally built.
