Structural engineering and sustainable design innovations are thriving in the academic climate of the University of Nevada, Las Vegas (UNLV). With the recent completion of Greenspun Hall, the university will likely earn its first Leadership in Energy and Environmental Design (LEED) Certification. And although located on the eastern edge of UNLV’s campus, Greenspun Hall is at the center of sustainable curriculum.

At Greenspun Hall, structural innovations abound. To maximize its prominent location, a 125-foot-tall tower revealing the letters UNLV announces to students, teachers, and the community that they have arrived. A canopy supporting photovoltaic cells cantilevers 70 feet above a suspended plaza to provide relief from the desert climate, and a cantilevered cast-in-place concrete stair brings a sense of airiness into a courtyard that is surrounded by structure.

Greenspun Hall is the $94 million, 120,000-square-foot home for the Greenspun College of Urban Affairs and is the fifth largest academic facility on campus. In addition to providing classrooms, faculty offices, and a 190-seat auditorium, the building will house high-definition media facilities for KUNV-FM radio and UNLV-TV. While these broadcasting facilities will not be ready until the fall, classes began this spring.

Greenspun Hall also bears the honor of receiving the largest single donation in the university’s history, $37 million, from the building’s namesake family. The Greenspun family has been active in the Las Vegas community and its media since the 1950s—the late Hank Greenspun was the founder and publisher of the Las Vegas Sun newspaper—and involved with the university’s College of Urban Affairs since it began in the 1990s. The family’s second generation, Brian and Daniel Greenspun, were active participants in development of the project’s sustainable design. Their passion for an environmentally friendly building has put Greenspun Hall well on its way to achieving a LEED Gold certification from the U.S. Green Building Council.

Structural creativity makes the grade
Two L-shaped towers project up from an almost square-shaped ground floor podium to create this multi-level building consisting of a cast-in-place concrete slab and beam system with ordinary reinforced concrete shear walls. While this scheme was developed to accommodate the architect’s request to minimize column sizes and maximize office space, the overall building layout was organized to address lighting requirements. The L-shaped towers, containing the classrooms and office spaces, are comprised of a single, narrow bay that is ideal for optimizing daylight, whereas the ground level podium is an area where lighting can be controlled. This space not only serves as the central point for the broadcasting facilities, but its roof functions as the floor for a courtyard bordered by the rising towers.

While this layout supported both the program and the LEED requirements quite efficiently, structurally it posed some challenges. For the gravity design, the single span beams had no continuity, reducing economy compared with multiple-span structures. Particular attention to beam sizes and reinforcement ratios provided an optimal design for the given conditions.

In the lateral analysis, which was governed by a Seismic Design Category C classification, the layout resulted in potential structural irregularities that were advantageous to avoid. The plan irregularities, created by the L-shaped towers, were resolved by simply placing expansion joints at the reentrant corners, converting them into separate, rectangular floor plates. The vertical irregularities, caused by uneven mass distributions, however, could not be avoided in the design.

One source of unbalanced mass is the UNLV tower. This monumental structure soars 55 feet above the roof on the building’s east side and consists of a 57-foot-long, 11-foot-wide, steel braced frame system. At the top of this structure, on both the north and south faces, is a 6-inch-thick, 57-foot-long, 15-foot-high precast concrete wall element that serves as the backup system to the red sandstone façade. While light-gage steel is typically used for this purpose, the formation of the UNLV letters carved out of the sandstone called for a different approach. This method resulted in a unique shape that could not easily be framed out of the light-gage material. Instead, precast was used at this location, accomplishing a distinctive figure that now defines the building’s location.

The excessive weight of pavers, planters, and trees at the building’s plaza creates another area with a high mass concentration. Besides hosting creative architectural and landscaping elements, the courtyard displays structural inspiration as well. An 18-inch-thick by 12-foot-long cast-in-place bearing wall covered in red sandstone ascends 42 feet above the plaza floor into the desert air. The function of this wall is to support an exposed cast-in-place concrete stair that cantilevers 6 feet out from the wall to give the appearance that the stair is hovering above the courtyard.

The plaza also offers structural innovation in the form of a 70-foot-tall steel moment frame canopy. Built-up cruciform columns uphold the architect’s vision of a thin structure. The columns are comprised of two WT12 shapes welded to a W24 shape and are connected at the canopy’s top with a network of W21 beams. Each of these canopy members is galvanized, architecturally exposed structural steel. Because of strict provisions required for open, flexible structures, wind loads cause large lateral deflections forcing the canopy to be tied back into the structure. This signature structure serves as a beacon announcing the building’s presence from the ground and the air as the canopy is even visible to the naked eye when flying into the city.

Environmental awareness passes the test
Greenspun Hall was designed from the onset to be environmentally sustainable and to meet numerous LEED criteria. The structural credits being pursued for LEED certification fall into two categories: Energy and Atmosphere (EA) and Materials and Resources (MR).

The most striking feature influencing structural sustainable design is the tall canopy at the plaza level. Covering the majority of the building’s footprint, the signature canopy shades the courtyard, reduces the solar gain on the building façade, and the structure supports an array of photovoltaic cells that is among the largest in the United States. The photovoltaic system is a valuable source of renewable energy that provides 208,437 kWh annually and accounts for an annual cost savings of $21,532, or 13.3 percent, of the total energy costs. This element alone presents the opportunity for two points awarded for EA Credit 2: Renewable Energy.

The canopy is also a key factor in optimizing the building’s energy performance. The photovoltaic cells were carefully oriented and sized by conducting overshadowing studies and manipulating panel angles to achieve maximum utilization. Another factor is the building’s layout. Narrow floor plates allow high quality, natural light to enter the building, thus allowing a low-energy lighting system that uses daylight dimming to further reduce energy consumption. Both of these features, in combination with chilled beams and variable air volume (VAV) mixed demand-controlled ventilation, make Greenspun Hall 50.7 percent more cost-efficient than the LEED Baseline Building. This savings likely provides another eight points through EA Credit 1: Optimize Energy Performance.

A total of six points are expected in the category of Materials and Resources. Three of these points are for using recyclable materials. For MR Credit 4.1, 5 percent of the total material cost for the project must be realized by using recyclable materials, and for MR Credit 4.2, the criteria is 10 percent. These materials fall into two classes: post-industrial and post-consumer products. Fly ash replacement in cast-in-place concrete contributes to the former while structural steel and concrete reinforcement apply to both. The cast-in-place concrete specification requires a minimum of 15 percent and a maximum of 25 percent post-industrial fly ash, while the concrete reinforcement and structural steel specification call for a minimum of 55 percent post-consumer and 30 percent post-industrial recycled content. This combination results in a total of 24.7 percent recyclable materials as measured by cost. Because the building materials used in Greenspun Hall go well beyond the recycled material’s baseline criteria, an Innovation in Design Credit is being pursued as well.

Two of the remaining three points anticipated in Materials and Resources meet the conditions by using locally manufactured and harvested material, as outlined in MR Credits 5.1 and 5.2, while the third is achieved from an Innovation in Design Credit for greatly exceeding these requirements. Materials satisfy this requirement if they are manufactured, extracted, harvested, or recovered within a 500-mile radius from the project site. Cast-in-place concrete, concrete reinforcement, and structural steel were the main contributors. By cost, 50.5 percent of materials have been manufactured regionally and 52.7 percent have been extracted regionally. 

Sustaining the momentum
Greenspun Hall is not only a crown jewel at the University of Nevada, Las Vegas, but it has broken new ground in the discipline of sustainable design. Seismic constraints do not stand in the way. Tall cantilevered structures do not prove too difficult. UNLV has raised the standards for education facilities LEED certification. Though its most predominate feature is made of steel, Greenspun Hall is proud to be gold.

Leslie V. Hemby, P.E., LEED AP, is a senior associate and project manager for Walter P Moore, with 10 years of experience in diversified aspects of structural engineering analysis and design. She can be reached at LHemby@walterpmoore.com.
 

Q&A with the SE

Structural Engineer Editor Jennifer Goupil, P.E. (JG), interviewed Walter P Moore Project Manager Leslie V. Hemby, P.E., LEED AP (LH), regarding the structural challenges of UNLV’s Greenspun Hall.

JG: What was your role?
LH: I was the project manager. I was responsible for the successful project delivery; I led the project and managed the team during the design process.

JG: Who were the other team leaders?
LH: R. John Aniol, P.E, S.E., is the Structural Engineer of Record (SEOR).

JG: What was the size and type of the design team for Greenspun Hall?
LH: Our team included the SEOR, one project manager, three design engineers, and one CAD technician.

JG: What was the first task you needed to do to get started on the design?
LH: We needed to start at the beginning: determine the seismic design category, the structural system, and the structural materials.

JG: What types and how many structural systems did you and your team evaluate for this project?
LH: We evaluated six systems as follows:

• Scheme A: slab and beam concrete framing with shear walls, all mildly reinforced
• Scheme B: slab and beam concrete framing with shear walls, mildly reinforced with post-tensioned girders
• Scheme C: 5-inch slab plus 20-inch-deep pan joist concrete framing with shear walls, all mildly reinforced
• Scheme D: 5-inch slab plus 20-inch-deep pan joist concrete framing with shear walls, mildly reinforced with post-tensioned girders
• Scheme E: 5-inch slab plus 24-inch-deep pan joist concrete framing with shear walls, all mildly reinforced
• Scheme F: composite steel with braced frames

JG: Did your team perform cost estimates to evaluate different systems? If so, what did you learn?
LH: Yes, there was a cost consultant on board during the schematic design phase. We learned that pan joists are not a common type of construction in the area. The owner also had a cost consultant that came on board during design development, and the contractor was brought on board at the beginning of construction documents.

JG: How did you select the final structural system?
LH: Based upon price, a mildly reinforced slab and beam system was selected. The shear walls were preferred by the design architect to minimize column sizes.

JG: What was the most challenging aspect of the structural design? How was it solved?
LH: The wind provisions for open, flexible structures created the biggest challenge in controlling the lateral deflections for the canopy over the plaza. The layout of the beams for the catwalk and the photovoltaic panel support structure created numerous surfaces to accumulate load. In order to meet architectural and LEED requirements, the layout could not be adjusted; therefore, the lateral deflection issue was solved by tying the canopy into the structure.

JG: What lessons did you learn from the design of Greenspun Hall that you will apply on future projects?
LH: The wind provisions for open structures can add up if there are multiple wind surfaces. This is something to investigate early.

JG: Did this project have owner-required sustainable design goals? How did this affect the structural systems selection?
LH: Yes. This project is pursing LEED Gold Certification from the U.S. Green Building Council. To help achieve this, the concrete specifications were edited to include requirements for fly ash replacement (minimum 15 percent, maximum 25 percent). In addition, the concrete reinforcement and structural steel specifications listed requirements for regional (500-mile radius from project) and recyclable material (minimum 55 percent post-consumer and 30 percent post-industrial material).

JG: What engineering ideas did you implement to save project costs?
LH: The design architect wanted a cruciform shaped column at the plaza canopy for the tall cantilevered columns—providing an architecturally aesthetic structure with a thin appearance. Originally, built-up tubes were suggested with a tube frame at the top of the trellis as well. However, tubes were an expensive approach for this project; we recommended using W shapes to save money. We selected W24 built-up with two WT12 for the columns and W shapes for the horizontal trellis members at the top of the canopy as well. Ultimately, we achieved the look the architect wanted while maintaining economy.