Bridges Regularly Inspected for Safety
August 29, 2007
With the tragic August 1, 2007 collapse of the I-35W Bridge over the Mississippi River, there has been heightened public interest in bridge safety and in the condition of the highway bridges in the Port. Two of the three bridges are located within the Long Beach Harbor District: Gerald Desmond and Schulyer Heim. The Gerald Desmond Bridge has undergone numerous inspections and most recently was thoroughly inspected by State and County staff in April 2007. No serious imminent deficiencies have been found.
The following describes the three major bridges, their conditions, and plans for upgrades and replacements.
The Gerald Desmond Bridge was constructed by the Port in 1968. The Port owns the bridge and is responsible for its maintenance. It was seismically retrofitted in 1997, and the roadway was widened from four to five lanes in 2002. More than $30 million in federal funds were used for these two projects. In 2004, nets were installed under the bridge over roadways and Fire Station 20 to prevent falling concrete chips, some weighing up to four pounds, from injuring personnel. The Port is actively pursuing to replace this aging bridge with a modern cable stayed bridge. Meanwhile, repairs and maintenance will continue to keep operable this very busy bridge.
The Vincent Thomas Bridge was constructed in 1963 by and is owned by Caltrans. It is entirely within the Port of Los Angeles. It was seismically strengthened in 1998.
The Schuyler Heim Bridge is a lift bridge built over the Cerritos Channel by the Navy in 1948. It was transferred to the Port by the Navy and subsequently transferred to Caltrans in the 1970s. Caltrans and the Alameda Corridor Transportation Authority (ACTA) are currently planning to replace the lift bridge with a fixed bridge. The estimated cost of the replacement bridge and elevated truck expressway between the new bridge and Pacific Coast Highway is $728 million. Caltrans/ACTA propose to release a draft Environmental Document in August 2007. Caltrans is planning to seismically retrofit the bridge approaches this year, a $7 million project.
NATIONAL BRIDGE INSPECTION PROGRAM / BRIDGE RATINGS
On August 7, 2007, following news of the I-35 Bridge collapse, the LA County Board of Supervisors directed staff to report within 60 days on the condition of all bridges in the county they inspect and prepare recommended actions to the bridge owners.
Federal law requires that every public highway bridge be inspected every two years. The Federal Highway Administration (FHWA) funds Caltrans to inspect all bridges in California. City of Long Beach owned bridges are inspected by the Los Angeles County Department of Public Works (LADPW) under contract with Caltrans. Bridge inspection reports are delivered to the bridge owners, Caltrans, and the FHWA. Bridge ratings are published in a National Bridge Inventory (NBI).
The National Bridge Inventory (NBI) is used for preparing the eligible list of bridges for Federal-aid funding and for allocating bridge repair funds to states. Since each state may contain thousands of eligible bridges, an objective system to rate bridges is used. Each bridge is rated on three scales: a sufficiency rating (SR): a number between 0 – 100; and whether it structurally deficient (SD), or functionally obsolete (FO).
The most recent sufficiency rating for the Gerald Desmond Bridge is 43. The sufficiency rating of the Heim Bridge is 27.9. The Vincent Thomas Bridge has a sufficiency rating of 56.7.
The sufficiency rating (SR) is used primarily for prioritizing grant applications under the nationwide "Highway Bridge Program" (HBP). The SR rating measures the current ability of the bridge to meet functional and structural design standards. To be eligible for HBP repair funding, a bridge must have a SR less than 80 and be rated either SD or FO. If the SR is between 50 – 80 the bridge is eligible for just rehabilitation funding. If the SR is less than 50, it is eligible for rehabilitation or replacement funding.
REPAIRS TO DESMOND BRIDGE
The Port has contracted with LADPW to conduct initial repairs to correct deficiencies identified in previous bridge inspections. The condition of the bridge deck (riding surface) had been rated as "critical", level 2. Recent repairs are expected to raise this rating to "serious", level 3. The superstructure, the steel structure that sits on columns and supports the deck, has been rated as "poor", level 4, primarily due to spot corrosion.
Next phases of the maintenance program will further correct these problems. The bridge paint condition is poor, which will lead to more rapid corrosion. Maintenance costs on the bridge will increase in coming years. Staff believes, with regular inspections and repairs, the bridge can be kept in operation until the replacement bridge is open. However, within five years a decision whether to make major investments to paint the bridge (over $50 million) will be required.
APRIL 2007 INSPECTIONS
In April 2007 two additional inspections of the Gerald Desmond Bridge were performed: the normal biennial inspection by LADPW and a more intensive fracture critical member inspection by Caltrans. The biennial inspection relies mostly on visual inspection and tapping areas that the inspector can reach with a hammer. The fracture critical inspection examines pins and other critical areas whose failure could lead to a collapse. It requires specialized equipment. The frequency of these inspections has increased from every five years to every two years. Caltrans uses ultrasonic testing (high frequency sound similar to a sonogram) to search for hidden cracks in pins, and liquid dye and ultraviolet light to make suspected cracks in steel members more visible.
Caltrans and LADPW are currently preparing their inspection reports. Neither agency has identified any condition requiring the bridge to be closed. Caltrans may choose to make additional inspections. However, this may not occur due to the recent extensive work in areas on the bridge not normally accessed and correction of the most critical deficiencies. Again, nothing observed in the recent inspections or during the extensive repair work just completed indicated a need to close the bridge.
ADDITIONAL REPAIR WORK TO DESMOND BRIDGE
LADPW is preparing a proposal to perform additional less critical work. The durability of recent repairs will continue to be monitored. The monitoring program will establish what further repairs are needed to keep the bridge operational until a replacement is open. The contracting arrangement with the County has worked well. Staff will be recommending at a future Board date to continue funding repairs with the County.
Bridge Inspections, Terminology, and "Structurally Deficient":
A bridge will be rated structural deficient (SD) if the condition of one the three main bridge subsystems: the deck (riding surface), super structure (structure that supports the deck), or substructure (support columns and foundation) receives a condition level rating of 4 or less out of 9. A bridge will be rated functionally obsolete (FO) if the deck geometry, under clearances or approach alignment receives a condition level of 3 or less out of 9. A low bridge SR or a structurally deficient rating is not necessarily an indication of immediate danger. It indicates that there are bridge elements that need to be monitored and repaired. The recently failed I-35W Bridge in Minnesota had a sufficiency rating in the 50s and was rated structurally deficient. It is unclear at this time if the low sufficiency rating of the I-35W Bridge contributed to or had nothing to do with its collapse. A full forensic report by the National Transportation Safety Board may take a year or more to be complete. The only facts we do know at this time is the I-35W Bridge failed during rush hour, while a contractor was performing repairs. The early focus of the investigation has looked at possible fatigue or cracking of critical members, failure of gusset plates, lack of redundancy, and advanced corrosion. Again, until full details are known, it is difficult to pinpoint one or more contributory factors in the failure. However, the bridge was rated as structurally deficient. There are 3000 bridges in California with this rating. The US Department of Transportation on August 2, 2007 issued a "Fact Sheet on the I-35W Bridge Collapse" which stated:
-- "Structurally deficient means there are elements of the bridge that need to be monitored and/or repaired. The fact that a bridge is "deficient" does not imply that it is likely to collapse or that it is unsafe. It means they must be monitored, inspected and maintained.
-- Most "deficient" bridges are left open to traffic while it undergoes maintenance and repair.
-- If inspectors find unsafe conditions they will restrict access or close the bridge."
Gerald Desmond Bridge Inspections & Repairs:
The March 2005 G.D. Bridge inspection report on this bridge identified several major, but correctable deficiencies. The concrete deck was rated as being in a "critical condition" (level 2 out of 9), primarily due to large areas of damaged surface. There were many spalls (pot holes) and broken expansion joint steel fingers. If the condition rating had been an "imminent failure condition" (level 1 out of 9), the inspectors would have recommended that the bridge be closed. The superstructure was rated as poor (level 4 out of 9). This is primarily the result of advanced corrosion at a few locations. Pack rust, a thick layer of rust that can bend mating steel members, is cited at three locations plus at many of the rocker bearings (where the superstructure connects to a metal plate on top of a support column). No significant cross section loss was observed due to corrosion on major steel members. However, corrosion will occur at a more rapid rate due to the poor paint condition and this must be closely monitored. Another key deficiency was many corroded suspension cable socket keeper plates (they restrain the ends of the suspension cables from horizontal movement). The above deficiencies warrant the structural deficient rating for the bridge and are a primary reason for the sufficiency rating of 43. The bridge does not have vehicle breakdown lanes (shoulders) and its grade is greater than 5%. This alone would justify a rating as functionally obsolete. However, the FHWA rating systems does not rate a bridge for functional obsolescence if it is already rated as structurally deficient.
In January 2006, the Port issued a Purchase Order for $20,000 to the LADPW to conduct a pre-design survey and design repairs for the most critical items identified in the inspection report. Original designs were required to repair the broken steel fingers on the expansion joints. There was uncertainty whether any to the proposed deck repairs would be durable enough to last. It was agreed to repair several deck sections and monitor their performance. A final work plan and estimate was received from LADPW in November 2006. In December 2006, the Board of Harbor Commissioners authorized $200,000 for initial repairs to the bridge via a task order under the City’s existing contract with the County. Field work started in March and the repairs were completed in July 2007. A delay for preparing traffic control measures had an indirect benefit as it allowed time for testing the initial concrete deck spall (pothole) repair method. A few of the repairs failed. The cause was discovered and corrected and all the potholes were repaired using the improved method.
Work was completed during nine weekend days of partial and full bridge closures. Most of the work had to be done during daylight. LADPW repaired all of the critical items that had been identified: over 70 out of 104 suspension cable socket keeper plates, 120 spalls (potholes) in the concrete deck, 30 broken expansion joint steel fingers, and a recently damaged expansion joint on the connector from the southbound I-710. A program to monitor the durability of the deck repairs has been established, which includes the marking of bridge pier (support column) numbers on the median barrier. Vehicle ride on the bridge has been greatly improved. When repairing the 120 concrete deck spalls, no significant corrosion was observed of the deck steel reinforcing bars. Additional work performed by other contractors during the bridge closures included: new traffic striping, upgrading of the speed feedback signs, and repair of the street lights. Repair of the upper and lower suspension cable socket keeper plates required crews to access parts of the bridge that are not thoroughly covered in normal inspections. The LADPW bridge workers did not report any unexpected conditions in these less accessible areas.
Truck Weights and their Effect on Bridges
Federal and state law limits the weights of motor vehicles on highways to 80,000 pounds. Heavier and oversize vehicles that cannot be broken into smaller loads are allowed by permit. Each bridge is given a rating by bridge engineers as to the maximum size permit load that it can carry. Trucks cause more wear to roads and bridges than cars. Millions of repetitions of heavy loads on a bridge can lead to metal fatigue cracks. Inspectors monitor for these cracks. There is a very high percentage of heavy trucks on harbor area roads. The Schuyler Heim and Gerald Desmond Bridges and several local roads have been designated in a special overweight permit vehicle system established in California Vehicle Code Section 35700.5 and Long Beach Municipal Code section 10.41. This allows vehicles that are heavier than the legal 80,000 pound limit and carry ocean containers to weigh up to 95,000 pounds, provided they meet other conditions. Permits for the Schuyler Heim Bridge are administered by Caltrans. Permits for the Gerald Desmond Bridge are administered by LA County and the COLB Traffic Engineering Division. Currently, there are 89 special trucks permitted under this program by the COLB. The Long Beach truck routes on the system were approved by the City Council and Harbor Commission. There are no current load restrictions below legal loads on either bridge and both bridges allow overweight permit loads. The Heim Bridge had had a truck weight restriction, but it was removed after the deck was recently repaired.