Pasadena City Hall Overhaul Is a 'Thinking Man's Project'

The $80 million seismic retrofit and restoration of the 78-year-old Pasadena City Hall will include installation of friction-pendulum, double-concave base isolators, each weighing 2.5 tons. The 240 base isolators will support the entire weight of the 45,000-ton building.

By Greg Aragon

The 190,000-sq.-ft. Pasadena City Hall is located on Garfield Avenue, two blocks south of the 210 Freeway. The "California Mediterranean-styled" building was completed on Dec. 27, 1927, at a cost of $1.3 million (photo by Greg Aragon).

After nearly 80 years of public service, Pasadena City Hall is finally getting some support-structurally speaking, that is.

"This is one of those projects that people want to be a part of because it's seismic [and] the building is old," said Jim McLamb, vice president of operations for Clark Construction of California, about the $80 million effort to seismically upgrade and rehabilitate the city's majestic icon.

"It's a thinking man's project," McLamb added. "You don't go in there like a bull in a china shop. You walk in and strategize for a month and then you start it."

The 190,000-sq.-ft. Pasadena City Hall is located on Garfield Avenue, two blocks south of the 210 Freeway. The "California Mediterranean-styled" building was completed on Dec. 27, 1927, at a cost of $1.3 million.

Building a new foundation

Clark Construction, the current project's general contractor, broke ground in March, when its crews began digging to a depth of 9 ft. to demolish the structure's basement slab. Once this hefty phase is complete, crews will build a new 100,000-sq.-ft. slab and foundation that will sport 240 base isolators, which will protect the building from significant damage during a large earthquake.

"It's hard to give a magnitude scale but this [base isolation] scheme is for a 500-year earthquake," said Steve Marusich, senior engineer with San Francisco-based Forell Elsesser, the company serving as the project's structural engineer.

"The [retrofitted] building was designed to move a maximum of 30 in. for the maximum credible earthquake, which is likely to occur at the site, based on its distance from known faults and the capacity of those faults to generate large earthquakes."

After the 1991 Sierra Madre earthquake, Dames & Moore, a Los Angeles-based engineering firm, released a report that found structural and non-structural damage to city hall's dome and various parts of the building.

Then in 1995, after the 1994 Northridge earthquake, findings by Forell Elsesser found: "The performance of Pasadena City Hall in a major earthquake is expected to be poor; the estimated large, inelastic displacements are typically well beyond the capacity of the existing structure and may result in serious life safety hazards and the potential for localized structural instability."

"When we're done, the building will stay put if there is an earthquake and the ground will move around the building," said Clark project executive Dennis Breen, who is working on his first base-isolation project.

The base isolator used on this project is called "friction-pendulum, double-concave," which means that in the event of a major earthquake, the building will move like the pendulum of a grandfather clock, up the slick sides of the concave isolators and then back to its original position.

Designed and built by Vallejo-based Earthquake Protection Systems Inc., each isolator measures 3.5 sq. ft. and weighs about 2.5 tons. When all of the isolators are installed, they will support the entire weight of the 45,000-ton building.

Preserving the historic integrity

Marusich said that base isolators were used on this project primarily because the building is "historic and very massive," which lends itself to base isolation.

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"If we tried conventional retrofit schemes, which entail putting in concrete shear walls and things of that nature, [which] are very intrusive, we would end up losing a lot of historic features to accommodate the structural strengthening," Marusich added. "And the city wanted to keep [city hall] as pristine as possible. [Base isolation] is one of the few options that's available to achieve that goal."

He said that with this method, at least 75 percent of the structural work is hidden in the basement level and in the foundations.

Listed on the National Register of Historic Places, Pasadena City Hall is constructed of reinforced concrete with stucco rendering, elaborate cast stone ornamentation and tile roofs.

The building was designed by the San Francisco architectural firm of Bakewell and Brown, which turned to the Renaissance style of 16th Century Italian architect Andrea Palladio for inspiration.

Architectural Resources Group of San Francisco is the project architect for the current seismic upgrade and restoration.

Featuring 235 rooms, the rectangular-shaped, three-story city hall stretches 351 ft. between its north and south sides to 242 ft. between its east and west edges. On the east side is a one-story arcade, and on the other three sides are small towers at each corner and a signature, six-story dome towering 206 ft. above the main west entrance.

A friction-pendulum, double-concave base isolators like this one will be installed below Pasadena City Hall (photo courtesy of Forell Elsesser).

The building wraps around a Spanish Colonial-themed courtyard, which features a 22.5-ft.-tall cast stone Baroque fountain; paths of crushed granite-lined flower beds; cloistered arches paved with red Padre tile; and numerous California live oak trees.

Clark's crews recently demolished the arcade and courtyard after removing the fountain (which will be put back when construction is finished) to insert base isolators underneath, and have dug a 6-ft.-wide "moat" around the entire perimeter of the project to allow for horizontal movement in a quake.

Crews also have removed the large steps to the main entrance in order to install steel slider plates beneath them and have covered the original sidewalk in front of the building to protect it during construction.

On the exterior, crews will refurbish all cast stone elements, plaster and copper cladding on the dome. And on the inside of the building, they will restore an original elevator cab, as well as replace all mechanical, electrical and plumbing systems.

The retrofit project was approved by City Council in 2003. It is being paid for through a combination of Federal Emergency Management Agency funding, state grants; local tax revenues; bond sales, private contributions and an increase in the percentage of electricity revenues that are transferred from the city's light and power fund to the general fund annually.

The project is currently about 15-percent complete, with basement demolition finished and excavation in progress. The entire project is scheduled for completion in summer 2007. Until then, all City Hall offices will remain in temporary bungalows across the street.

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