The International Information Center for Structural Engineers

Friday, 12 October 2018 01:00

Structural flaws in San Francisco skyscrapers: Report for building code modifications

Written by  TheStructuralEngineer.info
Millenium Tower leans 15 inches Millenium Tower leans 15 inches

The 58-story Millennium Tower and the new-built Salesforce Transit Center developed severe issues and could be inadequate in case of a massive earthquake.

Millenium Tower is continuously sinking into its base ground and is currently tilting about 15 inches toward adjacent skyscrapers. In addition, Salesforce Transit Center is closed due to large cracks that appeared in supporting beams.

At the same time, a group of engineers stated that San Francisco's building codes were not capable of dealing with a large earthquake, calling for the inspection and upgrapde of the existing skyscrapers. According to the report, skyscrapers should be designed with higher stiffness Current regulations allow a 300-foot building to oscillate 6 feet from side to side during a large temblor. This flexibility may be beneficial for the bearing structure but it causes major damage to other parts of the building like the walls or the elevator systems. The calculations showed that stiffness should increase by almost 100%. Mechanical and electrical facilities should also be improved. Lucy Jones, one of the state's most prominent earthquake specialists who has been advocating stronger building codes said: "What you are seeing here is the city's recognition that it cannot protect their citizens from the biggest earthquake without dealing with these issues." San Francisco's board of supervisors will soon evaluate the report and if its recommendations are accepted, they will be implemented in the next revision of the city's building code in September 2019.

San Francisco is an earthquake-prone zone surrounded by active faults (including San Andreas) that are capable of delivering massive earthquake and cause severe damage to constructions. The problem with the current regulations is that they created when San Fransisco was not such a populated area and the main focus was on protecting lives rather than establishing a secure building after a severe earthquake. The report states that it would need 2-6 months to fix a costruction designed with the current codes if it was struck by a tremblor. Nowadays, such a delay is inacceptable, especially in buildings that housecompanies and this is why numerous experts believe that the building codes should change, making San Fransisco the first city in the U.S. that applies such a construction design. 

Source: NYtimes.com

 

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