Business at the ports expanded with the completion of the Panama Canal in 1914, and again following the economic boom in south-east Asia after World War II, and it continues to expand today as a result of increased trade with China. The ports are working together to address the challenges associated with these increased volumes. This has involved directing a great deal of effort at improving intermodal transportation at the ports. The Alameda Corridor which was completed in 2002 provides unrestricted railway access to and from the ports through the city of Los Angeles. The corridor eliminated more than 200 at-grade railway crossings. By 2020, predictions suggest that 100 freight trains a day will visit the ports. They are also working with the California Department of Transportation to transfer their roads and bridges to state control so that Route 47 can be extended across Terminal Island and provide a direct link for trucks to the interstate highway system. The ports are also working to improve pipeline transport of goods and to automate the identification, storage, and transport of cargo as it moves into and out of their facilities.

One of the many problems that the harbourmasters must address is the risk from a variety of seismic hazards. There are several faults within a few kilometres of the ports, and one fault that goes right through the Port of Los Angeles. Moreover, the ports were built from loose, wet material that is subject to liquefaction and failure. San Pedro Bay is also at risk from a tsunami caused by earthquakes occurring anywhere in the Pacific as well as from nearby submarine landslides. Ensuring these hazards do not cause the ports to have to be closed after an earthquake may be difficult. The magnitude 6.4 Long Beach earthquake in 1933 occurred on the nearby Newport-Inglewood fault. It killed more than 100 people, caused millions of dollars worth of damage, and changed the way that bridges and buildings are designed for earthquakes. Similar earthquakes took place in 1855, 1812, and in 1769; a recurrence interval of approximately 60 years. Hence earthquakes are expected at any time on one of the faults that surround and cross the island.

After the 1995 earthquake in Kobe, Japan, the city’s large port was disabled not only by damage to cranes and other port infrastructure, but by damage to highway and railway bridges that prevented the movement of goods into and out of the port. It took years to repair all of these bridges, by which time much of the container traffic had moved to the port at Hiroshima. But a performance-based design, in which ordinary bridges are designed to remain in service after small earthquakes while important bridges are designed to remain in service after large earthquakes, could be used to keep vital lifelines like ports in service following such disasters. However, designing bridges not to collapse is cheap and straightforward while designing bridges to stay in service is more difficult and also very expensive. Furthermore, deciding which bridges are most important is often influence more by politics rather than science.

Railway bridges are designed for three levels of earthquakes: for a moderate event, train safety is required; for a large event, structural integrity is required; and for an intense event, the bridge must not collapse. The return periods for these earthquakes are determined by calculating the bridge's importance, which is based on such things as whether hazardous material is being carried on a bridge (in a heavily populated area) and how many passengers go over the bridge every day.

Caltrans uses a peer review panel to determine the appropriate ground motion used to design, or retrofit ‘important’ and ‘non-standard’ bridges for the safety evaluation and the functional evaluation earthquakes. However, most bridges are categorised as ‘ordinary’ and designed not to collapse for a rare earthquake in the belief that this will keep it in service for smaller events. Caltrans is still working to determine if special design criteria is required for bridges on designated ‘lifeline’ routes. At Caltrans, one of the following criteria must be met for classification as an important bridge; the bridge must remain in service for post-earthquake seismic safety; bridge closure would cause an unacceptable economic impact; the bridge is formally designated as critical by a local emergency plan.

Three highway bridges and one railway bridge connect Terminal Island to the mainland. The Vincent Thomas suspension bridge was designed and built by Caltrans in 1963 and has a 460m main span, 45m vertical clearance over Cerritos Channel, and connects the west side of Terminal Island to the city of San Pedro. This bridge was analysed by Weidlinger Associates and retrofitted almost ten years ago to prevent collapse in the event of a very large earthquake. Although this bridge was not considered an important structure and was not designed to remain in service, it should still perform well even during the most extreme event. The design ground motion was large, because the Mw = 7.4 Paleos Verdes fault passes between the towers. A recurrence interval of 950 years, with peak rock accelerations of 0.97g horizontally and 1.05g vertically was estimated for this site. The 1992 Landers, California ground motion recorded at Lucerne was used and modified to match the target spectra. To account for near-field directivity, a large pulse was put into the time history at about 10 seconds and to address the fault slip, the bridge was designed for a 2.7m offset occurring over 5 seconds. The bridge was modelled using Adina, checked for damage, and then the model was modified with the proposed retrofit and rerun.

The retrofit design included reinforcement of the towers with doubler plates, to prevent buckling due to the high stresses in the towers. There was no retrofit of the pile foundations, which will rock slightly during a large earthquake. The cable saddle was also retrofitted to provide greater shear strength, along with devices to control the transverse movement of the truss. A new concrete deck, with a 7.9m-long expansion joint and hydraulic dampers, was added to allow longitudinal movement between the stiffening truss and the cable bent.

Because of the large vertical motion at the side spans, structural fuses with hydraulic dampers were installed. These allow large vertical displacements while limiting the forces to the adjacent stiffening truss members.

At the deck, slotted plates were installed between the deck and truss to provide added strength without overstressing the truss. Hydraulic dampers were installed to control the amount of movement between the truss and the tower.

But since then, routine inspection of the bridge revealed that some of the hydraulic dampers were leaking, perhaps due to an installation problem, and they had to be replaced. The introduction of new technologies requires a learning curve, but it is hoped that devices such as dampers will allow bridges to remain in service after large earthquakes.

The Gerald Desmond Arch Bridge was built by the Port of Long Beach in 1968; it has a 125m-long suspended main span, 48m vertical clearance over the Back Channel, and connects Terminal Island on its east side to the city of Long Beach. This bridge has developed various maintenance problems and the Port of Long Beach has suggested it would be more economical to replace the bridge with a new cable-stayed bridge with 61m of vertical clearance. This would allow access to the port for even the tallest container ships and would be the first long-span cable-stayed bridge in California. In order for the bridge to be so tall, long approaches are required to allow heavy trucks to cross the structure. A joint venture of Parsons Transportation Group and HNTB is performing preliminary engineering for the main span and the approaches.

Because the port would like State Route 47 to continue across the island and speed container trucks onto the Interstate Highway System, it is hoping to transfer this bridge to Caltrans’ ownership once it is built. Therefore, Caltrans and the port are working together to ensure that this bridge meets all Caltrans’ requirements. Like the Vincent Thomas retrofit, it is being designed to prevent collapse in an earthquake with a 5% probability of being exceeded in 50 years - a 975-year earthquake. The towers have steel shear links between the legs, similar to those designed for the signature span of the new East Oakland Bay Bridge, which will absorb energy and reduce displacements during large earthquakes. These shear links will require testing. The hollow concrete piers on the approaches, tension ties at the top of the towers, expansion joints between the main span and the approaches, and many other details will also require testing or further study. The seismic criteria is still being written, but Caltrans is treating it as an ordinary structure and has not required a functional evaluation earthquake. But to protect the port’s considerable investment, they will probably include a design to allow the proposed bridge to remain in service for more frequently-occurring earthquakes. If all goes to plan, the environmental documents will soon be approved, design should begin by early 2008, and construction of the proposed bridge is intended to be completed in 2014.

The Commodore Schuyler F Heim vertical lift bridge was built by Caltrans in 1949 and runs parallel to the Badger Avenue vertical lift railway bridge, built in 1998. Both bridges have a 55m-wide navigation channel and a vertical clearance of 50m over Cerritos Channel, when raised. They connect the north side of Terminal Island to the city of Wilmington, and form a barrier to container ship traffic travelling between the two ports.

The Schuyler Heim Bridge has a grated steel deck; the heavy trucks that use it have worn out the deck many times since it was built. These trucks are getting heavier and the new AASHTO LRFD bridge design specifications have load factors that may prove too small. Professor Dennis Mertz at the University of Delaware is carrying out a study of vehicles at the ports and determine if the load factors need to be increased. In 1997 a research project involved replacing parts of the deck with composite materials to eliminate the corrosion from the salt-water environment. Martin Marietta Composites in Raleigh, North Carolina fabricated fibre-reinforced polymer deck panels for the bridge, which has a custom 125mm-thick deck and is arranged in eight panels measuring 1.8m by 10.9m. Instrumentation was installed in the panels to facilitate long-term monitoring of the deck.

Another problem with this bridge are the timber piles in poorly-consolidated fill at the abutments, which are at risk of failing during an earthquake. Due to these problems, Caltrans District 7 is anxious to replace the bridge as soon as possible, before the next earthquake occurs.

The Caltrans design for the new main span involves replacing the lift bridge with a prestressed concrete box girder bridge on new pile shafts. The substructure would have an increased diameter underground to force plastic hinging during an earthquake at locations that can be readily seen and more easily repaired. Another alternative is to put friction-pendulum bearings between the shafts and the superstructure in order to protect the bridge by absorbing energy during an earthquake. Because they are self-centring, the bridge could remain in service. The Port of Los Angeles would prefer this alternative since it would offer the best chance of being able to move trucks through the port following an earthquake. However, the cost of these expensive bearings may make such a retrofit unfeasible. Caltrans and the port may also have trouble getting the bridge approved by regulatory agencies since it would increase the number of traffic lanes, increasing air pollution in the already smoggy San Pedro Bay. Because the replacement structure would not have a lift span, ships would be limited to a vertical clearance of about 14m and a horizontal clearance of 55m, which limits the size of the vessels that would be able to go through Cerritos Channel. The type selection meeting for this bridge is scheduled for July.

Both ports would like to have at least one highway bridge capable of remaining in service after the next large earthquake. This is particularly important for the Port of Los Angeles, which has most of its facilities on Terminal Island. All of the highway bridges are being designed (or retrofitted) to survive very large earthquakes, but only the Badger Avenue railway replacement bridge was specifically designed by HNTB for both an operational-level (15% in 50 years) as well as a safety-level earthquake (10% in 50 years).

The former bridge was a two-leaf bascule truss with a 70m main span that was built in 1924 and the replacement structure, built in 1998, is a single span vertical lift bridge, which unlike the Schuyler Heim Highway Bridge has its approach on grade. Although a single span railway bridge is a very stable seismic design, movable bridges are sensitive to ground shaking and often require repairs before they can be put back into service. After the 2001 Nisqually earthquake, most movable bridges in the region were damaged as a consequence of either finger joints locking together, shim and locking device damage, counterweights impacting towers, or leaky hydraulics. But designer Nien Wang said that since this bridge is a railroad structure with a very simple steel deck, many of these problems have been eliminated.

Even if the ports and their bridges remain in service following an earthquake, moving goods through Los Angeles may take a few days. After the 1994 Northridge earthquake, Los Angeles was able to quickly recover due to the many contractors willing to expedite repairs and because of the redundancy of roads and highways through the area. If one expressway is closed, there are two or three others that may still be open. Even if all the expressways are closed, traffic can be detoured onto surface streets and around damaged bridges. Therefore, it seems likely that if the ports are still in service and they have relatively undamaged bridges they should be able to get back to business in a few days.

The main seismic hazard at Terminal Island is very strong ground shaking due to faults near the ports. Also, there may be a surface rupture of the Palos Verdes fault going through the Port of Los Angeles and under the Vincent Thomas Bridge. Although suspension bridges are very flexible, three or four metres of offset between the towers may make the bridge difficult to drive on. Many of the port facilities could also be damaged by a large surface offset. Another seismic hazard of concern is liquefaction of the soil in San Pedro Bay. Most of the bridges are supported on deep piles that should protect them from soil failure, but Schuyler Heim is on short timber piles on weak soil that could cause damage during a large earthquake. The plan is that the new bridge will be in place before the next earthquake occurs.

One other seismic hazard that puts the ports at risk is tsunami. Although San Pedro Bay is protected by a breakwater, it is thought that it would only act to dampen the long period tsunami waves as they strike the bay. Consultant Moffat & Nichols has carried out a very detailed tsunami analysis of the region and found that the major source of tsunami in the Bay is not from a very large earthquake off the coast of Alaska or Chile, but from submarine landslides caused by a fault rupture near the coast. A slide offshore of the Palos Verdes Peninsula has the potential to produce a 7m run-up that could overtop the wharfs and cause some damage. Although, the run-up itself is not a major concern, more damage could be caused by the tugboats, tankers, and container vessels that the tsunami could pick up and throw against bridges and port facilities. There is little that can be done to protect a bridge from a vessel collision other than to try to move all vessels several miles away before the tsunami strikes. This may be difficult if the tsunami is generated only a few miles away.

This leads on to the final, and possibly most damaging seismic risk; that the ports are crowded with many pipelines whose failure during an earthquake could cause damage to adjacent structures. There are tanks filled with flammable and explosive liquids, high pressure pipelines, giant transmission towers, highways, railways, and waterways filled with vehicles that have the potential to damage bridges and port facilities during an earthquake. The ports may want to spend some time considering ‘co-location’ hazards and how to prevent adjacent pipelines from closing down the port during an earthquake.

Mark Yashinsky is a senior bridge engineer at Caltrans

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