Original designs for the Golden Gate Bridge were sketched
using pencil and paper. Now, more than half a century later, engineers
have delved into the high-tech world of three dimensional computer
animation to make the span better able to withstand the next big
Scientists have long known that bridges spanning
San Francisco Bay were vulnerable to quakes. Those fears were
confirmed in the 1989 Loma Prieta shaker, when a section of the
upper deck of the Bay Bridge collapsed.
The Golden Gate emerged unscathed, but the trembler
shook up the bridge district's directors enough to call for a
study of what might happen in the event of a really big quake,
like the one that leveled the city in 1906.
An analysis of the bridge's weaknesses was conducted,
followed by a retrofitting project to strengthen the city's most
One of the firms contracted to work on the project
was ISEC Inc., [karma2go, LLC] a tiny San Francisco company that
made its reputation doing failure analysis for oil companies.
As a subcontractor for Sverdrup Civil, a Walnut
Creek-based consulting/engineering firm, ISEC's [karma2go, LLC]
job was to concentrate on the southern end of the bridge, considered
one of the areas most susceptible to quake damage.
Using a powerful workstation on loan from Sun Microsystems,
ISEC [karma2go, LLC] engineers led by President Jawahar Gidwani
looked for the best ways to strengthen the viaduct, the anchorage,
the arch above Fort Point and the pylons supporting the arch.
By factoring in seismic stress, Gidwani could produce
a video simulation of what would happen to the bridge in an earthquake
measuring 8.3 on the Richter scale - bigger than the 1906 jolt.
Such dramatizations were used to test different retrofitting solutions.
"The technology has given us an insight that
was not possible before," Gidwani said. "We are able
to define the exact way in which structures will fail."
What would Charles Ellis, the engineer who led the
original bridge designers, have given for a a Sun Sparcstation
running eight powerful processors in parallel? Back in 1930, Ellis
did his calculations using slide rules and compasses.
To solve immense problems posed by factors such
as wind forces, weight of cars on the bridge and variations in
temperature, he had to devise new algebraic formulas - 33 in all.
Ellis produced an engineering marvel in the suspension
span itself. But the approaches were another matter. "In
the late '20s and '30s they didn't deal with dynamic loading such
as earthquakes and wind in the way we deal with them today,"
said Daniel Mohn, chief engineer of the Golden Gate Bridge District.
"They did a pretty good job on the suspension bridge, but
the approach structures are no better than other projects of that
"Today's technology enables us to identify
more closely the exact portions that need retrofitting,"
said Mohn. "Instead of going at the project shotgun-style,
we can zero in on what is deficient and just fix that."
Officials at Sun Microsystems say the technology
used by ISEC also could be used by insurance companies and government
agencies for risk management.
"From our perspective there's an entire market
opening up," said Tom Minot, a marketing development manager
at Sun in Mountain View. "Low-cost, high-performance computers
can perform analyses that were once inconceivable."
"Prior to this you would have needed a supercomputer,
so that people ended up either doing partial analysis or not analyzing
Design work for retrofitting the Golden Gate should
be completed by the end of next February, Mohn said, after which
construction can begin. The main problem remains funds. The project
is pegged at around $147 million, and the district has only about
$35 million. Hoped-for federal financing so far has not come through.
As published in San Francisco Chronicle (October 13, 1994)