The American Institute of Steel Construction (AISC) has awarded the American Physical Society’s headquarters expansion project this year’s IDEAS² Award for projects less than $15 million. This program recognizes projects where structural steel has been utilized in an innovative manner. The innovative use of structural steel may be in:
- the accomplishment of the building’s program
- the expression of architectural intent
- the application of innovative design approaches to the structural system
- the utilization of productivity enhancing construction methods
The American Physical Society (“APS”) has renovated their existing 30,000 SF editorial headquarters and added an additional 18,500 SF above it. This facility employs 150 people and is located in Ridge, NY. APS is a non-profit scientific organization founded in 1899 to “advance and diffuse the knowledge of physics.” The Long Island Pine Barrens Preservation Act prohibited expanding the building’s footprint hence the addition had to occur above the existing structure.
To meet the project’s $11 million construction budget, the leasing of temporary space and the relocating of employees were not planned; for the project to meet the budget, the operation of the facility could not be interrupted while the work was being performed. The entire construction, including columns, floor and roof framing, was built while the facility was occupied and in operation. The structural engineering involvement started in 2009 during unfortunate economic times. To minimize costs the structural steel was purchased and fabricated in advance and stored off-site in a controlled environment before it was required for erection. This strategy proved to be cost-effective even after including the storage cost.
The existing structure – footings, columns, roof framing and lateral system – did not have the capacity to support the loads imposed by a new second story. A long-span “bridge” over the existing structure would allow the new steel to be installed without disrupting the building’s ongoing use. The long-span design with a column grid – up to 38’ x 62’ – resulted in spacious, column-free, and architecturally flexible interiors and required minimal penetrations through the existing ground floor.
The majority of the new perimeter columns were located outside the walls of the existing building, creating an exoskeleton, although a few new columns were located within the existing courtyard. The W12 columns of the new frame are situated 5 to 9 feet outside the perimeter of the existing structure eliminating any interference with the existing foundations and allowing most of the new foundation work to be done outside the building. Only six columns penetrate the interior of the old building. These columns and footings were installed one at a time with limited impact to the occupied building.
The new second floor is elevated 4 feet above the existing roof, providing an interstitial space that serves both the existing building below and new structure above. The mechanical services were distributed efficiently from the rooftop equipment on top of the single-story building. The existing roof served as the working platform for the erection of the second floor framing.
The thermal analysis of the exoskeleton calculated differential expansion and contraction created by the temperature differences between the interior and the exterior of the building. All structural elements that penetrate the building envelope are insulated for the first 8 feet as they enter the building. A series of skewed W8x24 members brace the exterior beam-column connections not only to resist lateral loads, but also to dissipate the increased stresses caused by the temperature differentials.
The long-span design took into account the deflection, vibration and construction tolerances of the steel members. The 57 ft. long W24 filler beams span N-S between W30 – W36 E-W girders which in turn, frame into columns at the interior. At the north side, the girders are offset from the columns, serve as spandrels beams and are located within the building envelope. These spandrels frame into 62 ft long W30 beams at the N-S column line that extend through the envelope and connect to the exoskeleton columns.
The building’s lateral system consists of eight braced frames, which utilize diagonal HSS8x8 braces framing at three locations around the perimeter of the exoskeleton, two locations within the existing single-story section of the structure and three visually exposed locations at the new double-height interior atrium. The original one-story building was laterally upgraded by tying it to the new two-story structure so that the entire structure behaves as one.
New floor slabs consist of 2½” normal-weight concrete on 3” metal deck. To moderate deflection that occurs in long-span frames, the concrete was placed from the center of the diaphragm outward. The design called for slip joints at the top of all interior partition walls so that deflection under snow loads or other live loads would not impose load and cause interior partitions to buckle.
The exoskeleton supports a hung screen or eco-mesh made of 0.135” woven wire mesh with a unique bridge wire for stabilization, and is framed on four sides with durable 16 gage metal channels. These “green screens” will support the growth of native vines, eventually enveloping the complex in a green blanket. The screens also mitigate solar heat gain through the building’s façade.
The remaining exposed portion of the existing roof was converted into a light-weight green rooftop, over which shorter green screens are supported by HSS6x6 “eyebrows” that cantilever from the new second floor roof. A new second-floor terrace is designed to accommodate possible future expansion within that area. A new mezzanine level over the western portion of the atrium is suspended from the upper structure using W6 and W8 hangers. Interior steel was left exposed and fireproofed with intumescent paint.
This project was developed using Revit. While an experienced structural engineer is able to conceptualize how the various structural systems interrelate three-dimensionally, the 3D model enabled the client, architect, and MEP engineers to visualize the structure as well. A BIM consultant facilitated coordination between the design team and the contractors from the outset and reduced the duration of design development by avoiding major unanticipated interferences. It also enabled the structural engineer to verify the alignment of steel members within the construction documents and confirm the connections and load transfers.
The collaboration between the architect’s talent for aesthetic emphasis and the engineer’s innovative structural design resulted in a state-of-the-art, high-performance and cost effective facility. The clients are pleased with their new space, “a design that reflects timeless sophistication.” It is worth noting that the Chicago Athenaeum: Museum of Architecture and Design and The European Centre for Architecture Art Design and Urban Studies awarded The American Physical Society’s Editorial Headquarters with the 2015 American Architecture Award.
Owner/Client: American Physical Society
Owner representative: LePatner & Associates
Architect: Marvel Architects
MEP Engineer: AKF Engineers