State Orders Shutdown of Parking Structure : Safety: The 145 S. Broadway facility could collapse in a moderate quake, an engineer says. Severe shaking would threaten adjacent state office building, but it will stay open.

State officials have ordered the closure Sunday of a 905-car parking structure serving state employees Downtown after a structural engineer found that the facility could collapse under moderate shaking from an earthquake.

However, also acting on the advice of two engineers from separate firms, the state Department of General Services has decided to keep open the Junipero Serra State Office Building at 107 S. Broadway, which is next to the parking structure. The building houses about 1,750 employees and is frequently the site of large public hearings.

The building is stronger than the parking structure, the engineers said, although they cautioned that it too could fail in a “severe” earthquake. Still, they said, such a quake is unlikely in the next five years that the building is expected to be occupied. The state has plans to replace the building but has not said when.

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In a Nov. 14 letter to State Architect Harry Hallenbeck, Allan E. Porush, a structural engineer with the Los Angeles firm of Dames & Moore, said his firm had concluded that “even moderate intensities of earthquake groundshaking could result in unacceptable behavior” of the parking structure at 145 S. Broadway.

“Therefore, we would not be adverse to demolition of the . . . structure, or at least removal of the top three stories as a precautionary measure in the earliest practical time frame.”

Regarding the Serra Office Building and another adjacent parking structure on Hill Street, Porush said: “We have found that these two structures do not have adequate strength or ductility (flexibility to bend without breaking) to withstand the severe groundshaking intensities such as those that might, on average, occur once in 475 years.

“However, it is my opinion that the risk to building occupants due to continued use of the two structures for a five-year period is limited and acceptable.

“The reason for this opinion is that the probability of a major earthquake occurring in close proximity to the site within the next five years, and resulting in severe damage and adverse life-safety consequences, is sufficiently low. Therefore, we believe that immediate evacuation of the buildings is an unnecessary precaution.”

A second engineer, Saiful Islam of the firm of Englekirk & Sabol, concurred with that assessment on the office building and said that the 145 S. Broadway parking structure should be restricted in its use.

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In a Nov. 29 letter to the state architect’s office, Islam said of the office building: “The probability of a major earthquake which may result in severe damage and probable life threatening condition . . . is significantly less likely in the next five years than it is during the assumed design life of typical structures.

“Therefore, in our opinion, the probable performance of these structures in a major earthquake, which has very small probability of occurring in the next three to five years, should not be used as a criterion to decide whether or not these structures need to be evacuated immediately.”

Joel McRonald, a principal architect in the state architect’s office, summarized the decision on closing the parking structure but keeping the office building open as “just sort of playing the odds” based on the probabilities that moderate shaking may well occur but severe shaking is unlikely.

Porush said in an interview that severe shaking was defined by his firm as an earthquake that would cause a ground acceleration equivalent to 40% of the force of gravity. He gave no quake magnitude in defining severity.

He conceded that some acceleration readings in the Jan. 17 Northridge earthquake damage zone were considerably higher than 40%, but said that 40% was “about the average.”

“We see a 10% probability of such ground shaking Downtown in the next 50 years,” he said.

As for the assessment in his letter that such shaking would only occur once in 475 years, Porush said that is based on “standard consensus” governing the state’s building codes.

However, he acknowledged, the assessment of a 475-year interval in a severe quake Downtown “might be updated in the wake of Northridge.”

Some earthquake scientists have been cautioning since 1987, when the magnitude 5.9 Whittier Narrows earthquake struck southeast of Los Angeles, that the fault involved, the Elysian Park, runs just north of Downtown and could cause as strong as a magnitude 7 earthquake there, but they have not put a time frame on it.

State officials have told employees who pay $44 a month for parking at the garage to move out and either seek parking nearby or start riding public transit. Some employees said they have been able to find other parking for $50 a month.

The California Union of Safety Employees has expressed some concern regarding the status of state buildings.

In a Dec. 16 letter to the state Department of General Services, union official Miriam S. Doonan noted that the department has identified 37 state buildings and parking structures for earthquake safety upgrading.

Yet, she said, it has provided information on the status of only the Serra building and the two parking structures.

“I am asking for the risk level rating for each identified building,” she wrote.