Jefferson Green office building solves space shortage in Albuquerque, N.M.

As soon as the new Jefferson Green office building was conceived, it became the obvious choice for Dekker/Perich/Sabatini’s (D/P/S) new Albuquerque headquarters. The growing A/E firm of 192 professionals includes architects, interior designers, landscape architects, land planners, and structural engineers. The firm had outgrown its current offices and had even been forced to lease a secondary office annex nearby. With more expansion anticipated, the firm desperately needed a larger home to accommodate the entire staff. The site ultimately chosen sits along a tree-lined boulevard in Albuquerque’s Journal Center area, close to the firm’s existing offices. The south property line borders a landscaped, park-like public space, with trees and grass making it a rare shaded site in a high-desert environment. After the land negotiations were complete, the developer hired a contractor who in turn brought all of the major subcontractors, creating a design-build-assist collaborative venture.

The design team and the developer were all interested in creating a "green" building and focused on achieving a minimum of a U.S. Green Building Council’s Silver Leadership in Energy and Environmental Design (LEED) rating for both the building’s core and shell and the D/P/S tenant improvements. The building is expected to use 45 percent less energy and 30 percent less indoor water than a conventional building. Features that contributed to energy and water efficiency include a high-performance façade that provides excellent daylighting and views while minimizing heat gain, a high-emissivity roof, a highly efficient mechanical system utilizing underfloor air distribution, energy efficient lighting and appliances, operable windows, low-flow plumbing fixtures, and use of nonpotable water for irrigation. Product selections emphasized the use of recycled content and regionally fabricated materials, and a comprehensive construction-waste recycling program diverted almost 4,000 tons of waste from landfills. Low-emitting materials were also used for all interior adhesives, sealants, paints, carpet, and composite wood to protect the health of occupants. Over the course of design and construction, LEED goals and requirements were at the forefront of many design decisions. Much of the actual certification process involves carefully documenting design decisions and calculations and ensuring the use of correct materials and processes during construction.

The building pro-forma called for approximately 85,000 square feet on three stories. A rectangular floor plan, approximately 90 feet by 300 feet, was determined due to the suitability to the site, as well as to create an efficient floor plate for multi-tenant office use. The aggressive construction schedule favored utilization of a structural steel-braced frame superstructure with composite framing and metal deck slabs. After the building footprint was established, a column layout was collaboratively developed between the structural team, architects, and interior designers, with input from the steel fabricator. Bay sizes were chosen to maximize the efficiency of office layouts while bringing daylight and views to as many occupants as possible. The perimeter bays span 34 feet while the center bay is only 22 feet. Along the longitudinal building axis, 30-foot bays allow for efficient modular construction. The available lateral bracing locations were ultimately distributed around the building core elements, again to optimize the open-office plan.

Sustainable site

The geotechnical engineers determined early on that the site would likely receive a Site Class D for use with International Code Council’s 2003 International Building Code seismic design calculations. Since this would have a significant impact on the building structure, shear wave velocity testing was performed on the site. This testing confirmed their preliminary findings, and the team moved forward with Site Class D. Combining the site class with Albuquerque’s geological setting and the building configuration, Seismic Design Category D was deemed necessary; this triggered special seismic detailing for the lateral-force resisting system, ceiling supports, and other components.

A thick layer of engineered fill was specified beneath spread footings as an alternative to a more costly drilled-pier foundation system. This common geotechnical recommendation is ordinarily very easy to accomplish in Albuquerque. Because of LEED goals to minimize site disturbance and the design team’s desire to maintain a lush green shaded area behind the building, the overexcavation and engineered fill site preparation was a challenge. Ultimately, the team decided to move the building slightly away from the tree line and the extent of earthwork beyond the building perimeter was adjusted. This minor compromise allowed five large cottonwood trees to remain on the south side of the building, providing valuable summertime shading for the building, and a large outdoor deck used by employees for breaks, meetings, outdoor lunches, and special events.

Structural system

Initially, a lateral-force resisting system consisting of Special Concentric Braced Frames appeared to be the best choice for this building. As the bracing system design developed, it became obvious that large brace members, heavy gusset plates, and extensive field welding would be required to satisfy the latest AISC seismic design criteria. An updated pricing exercise showed that the steel fabrication and erection cost had exceeded the original budget and the design team was challenged to find a more cost-effective system. After a brainstorming session with the general contractor, the steel fabricator, and the concrete subcontractor, the team decided to study two alternative bracing systems: substitute buckling-restrained brace members in lieu of the conventional tubular steel braces, or utilize 10-inch-thick concrete infill shearwalls in the bays formerly occupied by steel bracing. This pricing exercise showed the original braced frame to be the most expensive, while the buckling-restrained braces and concrete shearwalls were virtually the same cost.

The Dekker/Perich/Sabatini architectural and interior design teams were informed of the situation, and decided to not only go with the shearwall option, but to architecturally expose them throughout the building shell. The concrete walls proved to be thinner than a metal stud and drywall-clad steel braced frame, so both aesthetics and floor-plan efficiency factored into this decision. The added benefit is a beautiful architectural/structural expression of the lateral bracing system. Normally, concrete shearwalls in a steel-framed building are constructed independently of the steel frame, and then the steel frame is erected around and attached to the concrete. This option was dismissed due to the amount of time required to form and pour the various wall elements, preventing other construction activity on the site. AISC code provisions required boundary elements on these walls, and the engineering team suggested erecting a complete steel frame, then simply infilling concrete walls between steel columns in the bays already "reserved" for lateral bracing. Wide flange shapes in the 10-inch by 10-inch range were already determined to be efficient columns around the building core, so the concrete shearwalls were designed to be 10 inches thick, and aligned to be flush with the edges of most columns. The concrete was tied to the columns with a combination of headed anchor studs and welded rebar dowels, which activated the steel as boundary elements for the shearwalls. Double beams flanking the shearwalls at each level allowed the walls to be poured easily, even after metal decking was largely in place. Shear transfer at the floor and roof diaphragms was achieved with a combination of headed anchor studs on the flanking beams and rebar dowels at the wall/floor intersection.

The shearwalls are located entirely around the building core. This facilitated use of an exterior curtain wall on the north and east elevations. A system of punched openings with 25-foot-wide, full-height tall window units in each 30-foot bay occur along the entire south wall of the building. Aluminum sunshades provide sun control and clear, high-performance glass provides natural light and views. Smaller punched window openings in deep recesses on the west exposure provide an added degree of sun control.

As the structural drawings approached completion, electronic file exchange was utilized between Dekker/Perich/Sabatini and the steel fabricator. Shared information included AutoCAD framing plans as well as 3-D structural frame model created using the RAM Structural System software package, from RAM International. The fabricator used this information to speed up pricing, shop drawings, and to rapidly respond to framing changes required for tenant improvement work within the building.

Blending mechanical with structural requirements

The developer and design team decided to incorporate a raised floor system for power and data cabling, as well as underfloor air distribution. Architectural, structural, and mechanical disciplines discussed opportunities to reduce the floor-to-floor height in response to the absence of overhead ductwork. Maintaining a clear-return air path into the twin-return air chases posed the biggest challenge. Return air needed to pass between 9-foot, 6-inch ceilings and the 24-inch-deep floor girders running longitudinally along each side of the middle bay of the structure. This was primarily a problem on the second floor since the first floor had a higher ceiling height requirement in the lobby area, leaving a more generous air path in areas with lower ceiling heights. The third floor also had larger clearances due to the sloped roof framing used to facilitate roof drainage. The floor-to-floor height at the second story was eventually set at 13 feet, 6 inches. After subtracting the 6-inch slab thickness, 16-inch raised floor system height and the designer’s desire for 9-foot, 6-inch ceilings, girders that were adjacent to return air chases were reduced from W24 to W21 shapes to allow more air to pass into the core area where the mechanical chases were located. Additionally, a lowered drywall soffit was constructed surrounding the building core. This allowed for an ample return air path. Along most of the building perimeter in Dekker/Perich/Sabatini’s office space, the suspended acoustic ceiling was deleted altogether to enhance the volume of the space and provide a direct path for air to return to the chases. It had the added visual benefit of exposing more of the structural system and increasing the height to allow indirect lighting along the perimeter.

In several locations, floor-level shearwall penetrations were required for supplemental supply air distribution into the underfloor plenums. Most of the air was supplied along sides of the chases that were not bounded by concrete walls, but careful placement and control of the duct size ensured that only minimal special reinforcing detailing was required around the wall penetrations. On the roof, much of the center bay was constructed with a concrete metal deck slab. This area supports the large rooftop, mechanical air handling units. The additional concrete mass serves to dampen vibrations and enhance acoustic isolation of the equipment.

The lobby

The building lobby combines a dramatic exposed structural steel stair, which is behind a clear glass curtain wall, and a two-story space that opens into Dekker/Perich/Sabatini’s second floor level. A stainless steel cable rail enhances the open feeling at the lobby overlook, and the beams framing the perimeter of the opening are flush with the second floor, creating a very thin profile when viewed from the lobby. The stair within Dekker/Perich/Sabatini’s office area was designed to allow easy circulation between the firm’s ground-floor lobby and conference rooms and the open, second-floor office. The staircase needed to be economically designed but significant enough to serve as the visual centerpiece of the open lobby. After several design charettes, a simple design utilizing four bent tubular steel stringers and treads made of glulam beams laid flat was chosen. It proved easy to construct and enhances the views through the lobby to the outdoor deck beyond.

Conclusion

Dekker/Perich/Sabatini moved into the building on September 5, 2006. The entire staff has been reunited in a facility that is an environmentally responsible and collaborative workplace. All of the disciplines shared in creating a space that respects and celebrates architecture, structural engineering, and interior and landscape design.

Chuck Hanson, P.E., is the principal in charge of Dekker/Perich/Sabatini’s structural engineering department. He has practiced structural engineering in Chicago, San Francisco, and has been with D/P/S since 1998. His primary goal on any project is to help create an integrated and honest architectural/structural solution. He can be reached at 1-505-761-9700 or chuckh@dpsdesign.org. Tim Hightower, P.E., is a project engineer with D/P/S and has been with the firm for more than four years. He can be reached at timh@dpsdesign.org.

Design & Construction Team

Project name: Jefferson Green
Owner: JCC-One, LLC, Albuquerque, N.M.
Architect and Structural engineer: Dekker/Perich/Sabatini, Albuquerque, N.M.
Contractor: Enterprise Builders, Albuquerque, N.M.