New Seismic Building Codes Being Drafted by Engineers

In an effort to make buildings more resistant to earthquakes, the state’s structural engineers Friday unveiled a major rewrite of the seismic design codes followed by government jurisdictions throughout the world.

While the public would notice few outward changes in building design, the revisions, after almost five years of discussions, would in many cases impose new requirements on engineers.

For example, it would require additional review and seismic testing of proposed designs for buildings that either hold large numbers of people or are considered essential for public safety. Currently such reviews and tests are not required. The new document explicitly lists the criteria to be used in deciding the best type of structure to withstand severe temblors in a given geographical area.

The so-called “blue book” of the Structural Engineers Assn. of California serves as the seismic design chapter of the nation’s Uniform Building Code, which sets the standards for building structures and is used by cities throughout the nation and around the world as a model for their building laws.

‘A Need to Strengthen’

“This is a major step and represents the state of the art in building design,” said Oakland engineer Paul Fratessa, who headed up the rewrite. “While I’m confident that present design and construction is good in California--among the best in the world--there’s a need to strengthen (codes) to make certain we do any improvements necessary.”

The California structural engineers group writes the seismic codes in the “blue book” because the state sits within the nation’s most severe earthquake zones. The new codes will be sent later this month for approval by the International Conference of Building Officials, which issues the Uniform Building Code. Fratessa said he expects little or no opposition.

“The costs (of meeting the new standards) are not exorbitant,” Fratessa said. “All revisions have raised costs, but these improvements are what we ought to be doing, so they ought to be supported.” The new seismic codes could be in use as early as next year, he said.

Fratessa said the revised blue book would require engineers to do more work in determining how well irregularly shaped buildings will stand up to shaking. Up until now, shaking tests for a 30-story skyscraper rectangular for the first 15 floors but tapered for the next 15 would be conducted as though the entire building was rectangular.

‘To Make the Point Clearer’

“The new book identifies various (design) irregularities and tells the engineers what modifications they must do in testing to make sure a quake won’t grab and jerk the building around,” Fratessa said. “The top engineers already do (the modifications) but we wanted to make the point clearer.”

Similarly, the revised codes specifically would prohibit what engineers call discontinuous seismic systems--those designs in which sheer walls and other strength devices do not extend through the entire building, as was the case with the Olive View Hospital, which collapsed during the 1971 Sylmar quake.

“We haven’t liked those designs being done for years,” Fratessa said. “But now we are telling people you just can’t do it.”

The code lists numerous types of building uses--hospitals, structures that store hazardous materials, hotels, schools, day-care centers, public assembly halls--that would require evaluation by a second structural engineer in a type of peer review. Further, the responsible engineer must specify how testing and inspection of the design would be carried out. At present, testing and inspection are optional at the wish of the building’s owner.

“A lot of owners do it regardless,” Fratessa said. “But we wanted to put teeth into this.”

Fratessa said success of the code will depend on the cooperation of contractors and owners. He serves as an adviser to contractor associations and will be explaining the code to their members.

“The engineer has to be out front in saying what must be done,” Fratessa said. “Everyone should be clear that the code is only the foundation.”