Magnificent Metal Mondays

pressbox.FOOTE_

With the college football season right around the corner we thought it would be great to feature one of the most picturesque stadiums in the country. Today, we travel to Berkeley, California 

which is home to the Golden Bears. Yes the stadium is a beautiful place to watch a Pac-12 game but what is most impressive is the Press Box. To read more about the press box see below:

Excerpt taken from The American Institute of Steel Construction names its 2013 IDEAS2 winners. AISC – October 01, 2013

Building Team

Owner: The University of California, Berkeley, Calif.
Architect: HNTB Architecture, Inc., Los Angeles
Architect: STUDIOS Architecture, San Francisco
Structural Engineer: Forell/Elsesser Engineers, Inc., San Francisco
General Contractor: Webcor Builders, San Francisco
Steel Fabricator: The Herrick Corporation, Stockton, Calif.
Steel Detailer: SNC, Compton, Calif.
Steel Erector: The Herrick Corporation,Stockton, Calif.
Consultant: Hassett Engineering, Inc., Castro Valley, Calif.
Photo: Tim Griffith

Built as a memorial to fallen alumni of World War I, California Memorial Stadium has been endured as one of the most picturesque venues in college football from its opening in 1923 to the present day. After it was discovered that the stadium was at particular risk in an earthquake, which is further exacerbated by the fact that the stadium sits directly over the Hayward Fault, the university undertook a large project to seismically retrofit as well as modernize the stadium. As a part of this project, the western stadium bowl was seismically retrofitted and modernized while keeping the existing historic perimeter concrete wall in place.

The “crown-jewel” of the project, however, is the new long-span two-story structural steel press box that floats atop the new west portion of the stadium. One of the main architectural design goals was to achieve a floating effect to the press box by reducing the number of press box supports to a bare minimum. The resulting press box structure is 375 ft long with two main spans of 100 ft long and end-span cantilevers of 33 ft.

The press box arches to follow the curvature of the existing exterior wall and is supported by four concrete cores (two at each end) and four center structural steel columns. The press box is two-stories with the first floor housing the print, radio, and TV media functions and the second floor housing a club space with views and seating facing the field as well as a dramatic 25-ft cantilevered balcony with a glass deck that faces campus with panoramic views of the San Francisco Bay and Golden Gate Bridge.

The main structure of the press box consists of a story deep space truss that is comprised of radial trusses that are supported by primary trusses which span between the concrete cores and center columns. The occupant load for the entire press box is over 1,700 people, and over 1,350 tons of structural steel were used in its construction. The overall construction cost for the project was $215 million, with the press box portion being $40 million.

Due to the close proximity of the active Hayward Fault, the seismic design of the press box and supporting concrete cores utilized several design innovations to allow for good seismic performance. The cores and press box structure were seismically separated from the surrounding bowl and allowed to move completely independent of the main bowl structure.

To alleviate large bending and shear forces and economize the design, the press box was supported on steel pins at the center of each core. These pins allow the press box to pivot on the cores and minimize damage to the steel structure. Each 7-in. diameter high-strength steel pin is sandwiched by five 100 ksi steel gusset plates. The entire press box structure is supported on 12 of these high-strength pin assemblies.

The top level club space of the press box has a 25-ft cantilever balcony framing off the main press box space truss supporting a walkable glass deck. This balcony structure is also a space truss comprised of numerous small diameter pipe sections. This balcony truss system, which includes seismic and out of plane bracing, has several multi-member joint connections with some joints connecting up to eight pipe members. Due to the complexity of these joints, coordination had to take place in a 3D platform between the fabricators and design team.

Due to the complex nature of the site and surrounding neighborhood, there was limited space on site to allow for erection and construction of the press box. To address this issue, one of the largest crawler cranes in the country (750-ton Liebherr crawler crane with 276-ft boom and 65-ft counterweight extension) was used to erect the main press box truss in five large segments. The main space truss of the press box was assembled and welded on the playing field, adjacent to the seating bowl. Carefully selected splice locations were determined to ensure each of the five truss segments would be within the cranes capacity for weight and reach. Each of the five segments exceeded 75% of the cranes capacity and therefore were considered critical picks. The largest pick of the five truss segments was 165 tons at 160-ft reach, which took the crane to over 95% of its capacity.

The modernization and seismic upgrade of California Memorial Stadium required careful coordination and collaboration between the construction team and design team to bring this state-of-the-art press box to rest elegantly on top of the renovated stadium bowl. The stadium was able to re-open on time for the 2012 football season.

 

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