The torchbearer carrying the Olympic flame to the stadium in Athens will be the first to cross the new Rion-Antirion Bridge, the world's longest cable-stayed bridge.

If, by some remarkable coincidence, an earthquake strikes that August day, Frieder Seible says the new bridge will be safer than solid ground.

Seible should know.

Dean of the UC San Diego Jacobs School of Engineering, Seible was hired as a consultant on the design of the bridge. Athens' new four-masted marvel of modern engineering spans roughly two miles across the narrowest portion of the Gulf of Corinth and connects the Peloponnesian peninsula to the Greek mainland.

Since the Athens region of Greece is an epicenter of seismic activity, the greatest challenge for the designers was to build an earthquake-resistant bridge. Seible was a natural for the job.

Internationally recognized for his innovative bridge designs and earthquake engineering, the UCSD dean has done the testing for the San Francisco Bay Bridge East Span now under construction and retrofitted San Diego's own Coronado Bridge.

He also has applied earthquake technologies to protect high-risk buildings from terrorist attacks. Seible said his lab made a proposal to bombproof the U.S. Embassy in Athens for the Olympics, but the government decided instead to build an entirely new building.

For the Rion-Antirion Bridge, the design engineers researched many structural systems to mitigate seismic forces. One of the most innovative design features of the bridge, noted Gefyra (the French engineering company that built the bridge), is a 2,252-meter fully suspended continuous deck that will move like a pendulum during an earthquake.

Also included in the design are four damping devices connected to the deck and the top of each pier that help limit the deck's movement during a quake while at the same time permitting significant movement between adjacent piers. The company says the bridge was built to absorb up to 2 meters displacement between any of its piers and to withstand an earthquake of over magnitude 7 on the Richter scale.

"The initial design was a very flexible design structure with lots of mechanical parts that would be difficult to maintain afterwards," Seible said. "We changed it to one continuous spread with no joints."

The difficulty of the engineers' task was compounded by the fact that the construction team never did reach bedrock in its drilling. Seible and his collaborators designed large, shallow foundations with pier bases of 90 meters in diameter -- the largest piers ever built for a bridge and reinforced 20 meters of seabed subsoil with metallic inclusions.

After two years of preliminary work on the design and installation of the construction site, actual building of the bridge began in early 2000.It was scheduled to be completed at the end of this year, but the last section of the bridge was lowered into place in May. To mark the occasion, the mayors of Rio and Antirrio met halfway on the bridge on May 29. But the structure will not be inaugurated until the torchbearer crosses it on his way to the Athens Olympic Stadium on Aug. 8.

Unfortunately, Seible won't be attending the Olympic opening ceremonies; he will be lecturing in Tibet.

"China is building a new freeway and rail system, including 10,000 bridges, through Tibet in five years," Seible said. "Tibet is a country with topography like Switzerland -- and as you can imagine, there's considerable seismic activity in the Himalayas."

Cable-stayed bridges

Cable-stayed bridges may look similar to suspension bridges -- both have roadways that hang from cables, and both have towers.

But the two bridges support the load of the roadway in very different ways. The difference lies in how the cables are connected to the towers. In suspension bridges, the cables ride freely across the towers, transmitting the load to the anchorages at either end. In cable-stayed bridges, the cables are attached to the towers, which alone bear the load.

The cables can be attached to the roadway in a variety of ways. In a radial pattern, cables extend from several points on the road to a single point at the top of the tower. In a parallel pattern, cables are attached at different heights along the tower, running parallel to one other.

From: Build a Bridge" by Nova On-Line at www.pbs.org/nova

The equilibrium of the structure lies on each and any pylon and thus, cable-stayed bridges may have one, two or more pylons. The Rion-Antirion cable-stayed bridge has four pylons.