SAN FRANCISCO (AP) — Engineers will have to do more wind testing on a model of the Golden Gate Bridge before the span is modified for a seismic upgrade project and a suicide barrier, officials said.
Testing done last month in a Canadian lab showed the bridge model performed well under a horizontal wind flow of more than 100 mph. But the bridge became unstable when the wind flow was changed by 1 degree, the Marin Independent Journal reported Friday.
Officials plan to add netting on the struts along the 1.7-mile bridge to prevent suicides. The span is also being seismically retrofitted.
Engineers are concerned that any modification to the bridge could affect how it performs in high winds.
"The cross section of the bridge is kind of like an airplane wing, so putting a net on it or changing things has an impact," said Denis Mulligan, bridge district general manager.
The bridge board last week approved a $216,500 contract with Rowan Williams Davies and Irwin Inc. for the wind testing work in Guelph, Ontario.
In terms of seismic work, the north and south ends have been retrofitted and could sustain an 8.3-scale quake. The center suspension segment was saved for last because it is least susceptible to collapse in a major quake, bridge officials said.
The suspension section could withstand a large earthquake, bigger than a 7.0, but there would be extensive damage and the bridge would likely have to be closed for a long period, they said.
About 110,000 people use the 80-year-old bridge daily.
Information from: Marin Independent Journal, http://www.marinij.com