City of San Jose
Richard Meier & Partners Architects
Englekirk Structural Engineers
Curtainwall Design Consulting
Turner Construction Company
18 stories, 550,000 sqft
Design/assist-design/build program including a custom unitized curtainwall system featuring louvers, sunshades and operable windows for the tower; cable truss system with point-fixed glass forming a 21,000 sqft rotunda
Rotunda glass is point-fixed and perforated at corners, tempered and laminated with a high performance low-e coating, with panels in the barrel area measuring approximately 6’ x 10’ with 13/16” IGUs (_ x .060 x _); by Cricursa
Richard Meier & Partners Architects are well known for uncompromisingly modernist designs both formal and monumental, featuring light-filled spaces and sweeping expanses of metal, stone and glass. Enclos has collaborated with Meier on many past projects, including the sprawling Getty Center museum in Los Angeles. For the San Jose City Hall project, Meier designed a slim 18-story metal and glass tower with an adjacent public plaza dominated by a free-standing dome topping a 10-story glass rotunda.
Michael Palladino, partner with Richard Meier and lead architect on the San Jose project, laid out the program for the dome. While the dome capped rotunda heralded the old tradition of building form in public buildings, Palladino wanted to combine this aspect with the use of state-of-the-art technology “beyond any skylight ever built.” His vision to “take the next step in dome design” with a highly transparent all glass structure by using a filigree tension based support system was truly monumental.
The decision was made to bid the tower curtainwall and rotunda as a single design/build facade package. With Enclos providing design-assist services, a concept was represented in the architect’s drawings and a performance specification was included in the project tender documents. Enclos was ultimately the successful tender for curtainwall contractor.
Curved glass is used in the lower barrel of the rotunda, with simple curvature required in one direction only. Compound curved glass to provide true curvature to the dome surface was considered but ultimately rejected for budgetary reasons. Instead, the dome surface is faceted with flat panel shapes hung from cable trusses. The rotunda's enclosure is unusual in its use of an exterior structural system to support the glass. Stainless steel cable trusses span horizontally between structural steel columns in the rotunda and the arched beams that form the dome. The sole compression elements in the system are the stainless steel spreaders that, along with approximately 2.5 miles of stainless steel cable, comprise the trusses. Spider-type fittings attach to the inside end of the spreaders, providing the point fixings that secure the glass. A detailed installation method statement was developed to facilitate assembly and installation of these cable truss systems, and required pre-tensioning forces up to 22,000 lbs. Hydraulic equipment was used to achieve these pre-stress forces.
Arguably the most challenging design aspect of this project was accommodating the large inelastic building drifts required by the new California Building Code in areas of high seismic activity. Conventional point-fixed systems can be inadequate in these applications, which lead Enclos to develop a new system involving a custom spider design capable of providing for large in-plane movement. The system allows for up to 3 inches of in-plane movement at each fixing. A custom spider component was required to accommodate this movement. Enclos developed a custom spider that is investment cast of a special heat-treated stainless steel alloy with mechanical properties well beyond the 316 stainless alloy typical to conventional spider fittings. An extensive testing and mockup program was undertaken for the spiders and dome structure, in addition to seismic, water and air infiltration.
At 100 feet, the rotunda’s diameter surpasses that of the U.S. Capitol building, and is virtually all glass. Through the structure's 12 bays — each 26 feet wide spanning between AESS structural steel arched beams, rising to a height of 108 feet — the project is able to reflect the transparency and openness of the democratic government in which the United States prides itself.