National Award - Sculptures/Art Installations/Nonbuilding Structures

The unique and innovative design of the East Bridge, utilizing an optimized box girder and suspended deck, results in a remarkably light and transparent structure, particularly given the 150 ft span. —2021 IDEAS² Judge Stephanie J. Hautzinger, SE, AIA, Associate Vice President, CannonDesign, Chicago

The Moscone Center is one of San Francisco’s key economic drivers and serves as a jewel box for the city.

A recent expansion of the center provides a collection of light-filled spaces that accommodate a variety of convention-related activities, vastly improving the facility and its campus while allowing it to meet the evolving needs of a modern city. The project includes two new pedestrian bridges, enhances its lively neighborhood, and attracts both residents and visitors alike with a pedestrian-friendly design that connects the adjacent Yerba Buena Garden’s new and existing open spaces, parks, and cultural facilities.

For the East Bridge and its tapered roof, steel box girders were the only solution that allowed for the required stiffness while achieving a narrow and tapering profile. The profile of the steel roof system was carefully studied, considering both structural and aesthetic drivers, with taper angles designed to minimize the visual profile of the bridge when viewing it from the street. Steel became a key part of the architectural expression of the East Bridge, and the steel rods and gusset plates were exposed in the bridge but also delicately integrated into the faceted glass enclosure.

The East Bridge was constructed on-site and then lifted into place in one day with limited street closures. The enclosed walkway is suspended by hanger rods from a built-up steel plate roof box girder, which achieves the 150-ft span while maximizing traffic clearance below and providing unobstructed views through the bridge along Howard Street. The bridge is seismically separated from the new building superstructure and includes its own steel concentrically braced frame and steel moment frame lateral system on the south side of Howard Street.

The final structure of the East Bridge uses a single optimally shaped, primary-load-bearing built-up steel plate box girder located along a central spine at the roof level. The bridge is integrally connected to the new Moscone South building structure and spans 150 ft to a buckling restrained braced frame (BRBF) on the north side of Howard Street. A system of hollow structural section (HSS) outriggers cantilevers from either side of the girder to support hanger rods at 6 ft on center along both sides of the bridge, and the bridge width varies from 30 ft at the ends to 23 ft at mid-span. The rods support 10-in.-deep rolled steel beams spanning the width of the bridge at Level 2, which act compositely with a 5-in.-thick composite metal deck slab, producing a floor structure of minimal depth.

In addition to the optimally shaped box girder, using HSS for the outrigger cantilevers maximizes the headroom under the bridge by transmitting gravity loads up to the roof level box girder and minimizing the thickness of the structure at the walking level. The width of the bridge is minimized at the center of the span, thus minimizing loads at the location of the maximum moment. These innovations, in combination with the lightweight cladding and finishes, make for a light and aesthetically elegant bridge whose form facilitates the flow of its users between the two buildings.

The West Bridge replaces an existing pedestrian bridge and connects Yerba Buena Gardens and the Children’s Garden. The wide pedestrian deck is supported on two tapering structural steel box girders and stands as a sculptural, open-air walkway that passes over the southwest end of Howard Street, with public art and landscaping to act as a continuation of the adjacent park and plaza spaces.

The West Bridge is also a steel structure, comprising a pair of long-span built-up tapered steel box girders. These girders support conventional rolled steel beams that span between them and cantilever beyond. The beams support a conventional slab on a metal deck, and the bridge is supported by an existing steel structure, with a sliding connection to create a seismic joint. The south end of the bridge is supported by a braced frame and is supported by the reinforced concrete substructure of Moscone South. This bridge was also constructed on the ground and raised into place on one weekend day to minimize the impact on traffic. Similar to the East Bridge, it is seismically separated from the Moscone South structure.

Pedestrians around the Moscone Center now enjoy the mid-block lights they’ll see on Howard Street. These lights change 30 times a second, turning red, yellow, green, orange, blue, purple, pink, and lavender. The idea is to celebrate the design of the bridge, activating the convention center and the surrounding area equally. The permanent LED light show is called Point Cloud and was installed by artist Leo Villarreal, who in 2013 turned the Bay Bridge into a nightly display of constantly shifting white lights. Similarly, Point Cloud is intended to be seen not only from up-close but also from afar, up and down Howard Street, from the nearby San Francisco Museum of Modern Art, and also from the buildings in the Yerba Buena district. The East Bridge also has a daytime presence, thanks to its enclosed steel and metal panel finishes and glass on both sides, adding a unique experience for conventioneers while creating an iconic reflective sky bridge above Howard Street.

Steel fabricator and erector: SME Steel Industries, West Jordan, Utah *AISC Member* *AISC Certified Fabricator* *AISC Certified Erector*
Steel detailer: Pro Draft, Inc., Surrey, B.C., Canada
Structural engineers:
Skidmore, Owings & Merrill, San Francisco
SOHA Engineers, San Francisco
Tipping Structural Engineers, Berkeley, Calif.
Architects: 
Skidmore, Owings & Merrill, San Francisco
Mark Cavagnero Associates, San Francisco
General contractor: Webcor Builders, San Francisco
Owners:
City and County Of San Francisco
San Francisco Department of Public Works
San Francisco Travel