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February 27, 2002

Three earthquakes, one tough building

  • The Legislative Building in Olympia was already due for a seismic upgrade. Then the Nisqually earthquake struck.
    Swenson Say Faget

    Legislative Building
    Courtesy of Swenson Say Faget
    In the Legislative Building, over 173 million pounds of stones, bricks and building finishes moved in response to the Nisqually earthquake. Structural damage was limited to the upper rotunda.

    In the 74 years since its construction, the state Legislative Building has withstood three major earthquakes -- in 1949, 1965 and 2001. This remarkable resilience is due in part to the original structural design, and more important, to a series of seismic upgrades undertaken in 1949, 1965 and 1975.

    Designed by New York City architects Wilder and White, the landmark building was completed in 1928 on the site of an earlier attempt at a state capitol in 1893. The House and Senate wings actually utilize the masonry wall and foundations from that first building.

    The four-story masonry structure comprises the House and Senate wings and north and south entrances, all connected to the central rotunda. The rotunda, the defining feature of the building, rises 220 feet above the main structure. Its outer masonry dome covers a similar interior masonry dome, resting atop a four-legged, table-like concrete structure.

    Hidden inside is a structural cone resting between the inner and outer domes, supporting the lantern on top of the dome. The familiar sandstone columns surrounding the building are freestanding structures. On the interior, plaster finishes can be seen on either brick masonry or hollow clay tile, along with marble veneer. Most of the ceilings throughout the building are suspended ornamental plaster.

    Earlier seismic upgrades

    It was believed the damage from the building's first earthquake, in 1949, was confined to the lantern, so it was eventually removed and replaced with a steel structure clad with the original sandstone. The lantern showed little damage following the 2001 quake.

    The next earthquake, in 1965, caused damage to the upper rotunda below the inner dome, and above the roofs of the House and Senate wings. The resulting cracks in the masonry walls were believed to be a continuation of undiscovered damage from the 1949 earthquake.

    Victor Gray of Victor Gray & Associates was hired to design the repairs. Gray’s upgrades consisted of a concrete cylindrical wall and steel trusses placed inside the masonry buttresses. In 1975, Gray designed seismic upgrades to the wings and entrances, adding new concrete walls and steel drag struts that tied the five portions of the building together.

    Five large stones

    Fast-forward to the morning of Feb. 28, 2001. When the 6.8-magnitude Nisqually earthquake hit, the Legislature was in session and large groups of school children were touring the building. Though frightened by the ominous sounds of over 173 million pounds of stones, bricks and building finishes moving in response to the earthquake, everyone exited the building without major injury. The 1965 and 1975 upgrades are the main reason the building performed so well and that no lives were lost.

    Five large stones, weighing 2,000 pounds each, moved away from the building. They were held in place by a patch mortar measuring less than 4 square inches.

    This time the structural damage was limited to the upper rotunda, the same area damaged in 1949 and 1965. The 30 million pounds of brick, stone and concrete above the table structure shifted horizontally up to three-fourths of an inch. Inspection of the damage revealed that the upper rotunda rocked and slid on the concrete table.

    The remaining damage occurred mainly on secondary structure and finishes, the most visible of which was to the exterior veneer on a buttress at the upper rotunda. Five large stones there, weighing approximately 2,000 pounds each, had moved horizontally away from the building. The stones were held in place precariously by a patch of remaining mortar measuring less than 4 square inches.

    The building was soon closed because of the potential for falling debris. The Legislature was relocated to cramped temporary quarters until the stones could be removed safely.

    The design team that had been working since 2000 on a proposed rehabilitation and seismic upgrade of the Legislative Building was on site within three hours of the earthquake. During the next six weeks, the team of Hardy Holzman Pfieffer (architects), Swenson Say Faget (structural engineers), Wiss Janney Elstner (material experts) and M.A. Mortenson (GC/CM) worked with the state in an effort to reopen the building.

    In addition to removing the displaced stones at the upper rotunda, the team installed retaining collars at the upper rotunda columns. Repairs were also made to the suspension system for the plaster ceilings and in numerous other areas.

    Better computer model

    Since the earthquake, the design team has been busy updating the seismic analysis to incorporate information learned during the emergency response. New animated computer modeling captures the behavior of the upper rotunda during the quake.

    While the previous analysis indicated the area was vulnerable, it did not predict all of the documented damage. The opportunity to refine the computer model based on actual damage is rare in earthquake engineering, and has been very exciting for the engineering team.

    Restraining collars
    Courtesy of Swenson Say Faget
    Restraining collars were placed on the Legislative Building's upper rotunda columns after they suffered damage from the Nisqually earthquake.

    The current seismic upgrades are moving forward, and will probably involve strengthening the upper rotunda as well as enhancing its connection to the concrete tabletop. The steel collars at the upper rotunda columns will probably be replaced with internal steel pins, restoring the building to its original architectural design.

    The current design team of NBBJ (architects), Einhorn Yaffee Prescott (historic architects), Swenson Say Faget, Wiss Janney Elstner and Mortenson is diligently working to release construction documents for the next set of upgrades, estimated for early summer.

    Current seismic technology and past earthquake history are invaluable in designing earthquake-safe buildings. By applying what we’ve learned, we can design structures that are able to withstand an even bigger seismic event than the one we experienced in 2001. Our goal is to continue to work on improvements to the Legislative Building, ensuring the safety of its occupants for years to come.

    Michael A. Wright is a principal with the firm Swenson Say Faget and is the structural engineer of record for the repairs and planned seismic upgrades to the state Legislative Building. He has been involved with the building since performing a preliminary seismic analysis in 1998.

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