| |
|
 Back to Previous Page |
|
California Dreamin'
 |
|
|
Stirling Lloyd, market leaders in structural protection technology, and their Eliminator® bridge deck waterproofing system have recently played an important role in the successful construction of a major new highway bridge in the USA.
Named after one of America's most famous iron workers, who gained notoriety after surviving a fall from the Golden Gate Bridge in 1936 and died in 2000 aged 95 years old, the Al Zampa Memorial Bridge is the first major suspension bridge to be built in the USA for nearly 40 years.
Following the 1989 Loma Prieta earthquake, the State of California Department of Transport (Caltrans) conducted a seismic review of all of their major toll bridges including the two multi-span bridges that crossed the Carquinez Straits, joining Northern California's Contra Costa and Solano counties. They concluded that although the 1958 bridge could continue in-service after a seismic upgrade, it would be more costly to upgrade the original 1927 bridge than to replace it.
The demand for the new bridge came about largely because of these findings compounded by the expected growth in the volume of traffic on Interstate 80. Adding extra lanes to the existing bridges was not an option and with traffic flows of approximately 105,000 vehicles per day being carried by the bridges, a figure forecast to rise to 128,000 by 2010, a new bridge was of paramount importance.
|
The decision to build the bridge was taken and Caltrans appointed a joint venture consultancy team of Parsons Transportation Group and Opac Consulting Engineers to undertake studies into the type of bridge required. Their proposal was a suspension bridge with a steel orthotropic deck, supported by two 124m (410 ft) concrete towers as opposed to the more traditional choice of a truss stiffened deck. Not only was this a more aesthetic and cost effective option, but it would also take less time to construct and have a far superior seismic performance.
Having convinced Caltrans of the benefits of this type of bridge, detailed planning went ahead. With a span of 1,056m (3,464 ft)and a width of 27.2m (89 ft) the deck, which was to sit 43m (140 ft) above the water, was to carry 4 lanes of vehicular traffic including a high occupancy vehicle lane together with a pedestrian/cycle lane. This would carry all westbound traffic on Interstate 80 between Vallejo and Crockett while all eastbound traffic would be carried by the remaining 1958 bridge.
Located some 20 miles northeast of San Francisco on three different active earthquake faults - the San Andreas Fault, the Hayward Fault and the Franklin Fault, seismic resistance was a critical consideration for the new bridge. Caltrans required the bridge to be designed to withstand the maximum credible earthquake from each of the three faults. Based on the Richter Scale these were given as 8.0 for the San Andreas Fault, 7.25 for the Hayward Fault and 6.5 for the Franklin Fault, making it the first ever U.S. bridge to be designed to such stringent seismic standards.
The contract to construct the bridge was awarded to a joint venture comprising of FCI and Cleveland Bridge, California, with the Parsons Transportation Group assisting Caltrans in addressing the construction issues of providing protection to the new deck.
By their very nature, steel orthotropic decks are a stern test for any waterproofing system. Not only are they livelier than conventional truss stiffened concrete decks but they are also subject to a greater level of expansion and contraction, as the heating and cooling cycle of a steel deck is considerably quicker than that of a concrete deck. Additionally, because of the need to reduce the dead load on this type of bridge, thin asphalt surfacing tends to be used with higher application temperatures than conventional surfacing. These characteristics allied to a heavily trafficked bridge, for which lane closures would not be acceptable and a structure that by its very nature necessitates high maintenance access costs all pointed to the need for the very highest level of protection for the deck against corrosion.
Parsons recommendation to Caltrans was Stirling Lloyd's Eliminator® bridge deck waterproofing membrane and Bond Coat SA1030, having witnessed the system's benefits on previous successful collaborations including the Queensboro and Williamsburg Bridges in New York, the latter being a steel orthotropic deck. Importantly, Stirling Lloyd could point to a proven, unsurpassed track record of successful applications on orthotropic steel decks both in North America and around the world. Structures protected include the George Washington Bridge that links New York and New Jersey (USA), the Mackay Bridge in Nova Scotia, Canada, the Forth and Severn Road Bridges (UK), the Tsing Ma Bridge (Hong Kong) and the two Bosporus Bridges linking Europe and Asia in Istanbul.
Eliminator® is a rapid curing, seamless, spray applied waterproofing membrane based on methyl methacrylate (MMA) resins with approvals from Highway and Rail Authorities around the world. The system's physical and in-situ performance properties would provide the solution to a number of potential problems facing the consulting team.
The large deck and air temperature fluctuations experienced could be readily accommodated, by the system and the Bay area sea fogs would not affect its cure, provided that the deck temperature was above dew point. The system's speed of application and cure, together with its toughness, would solve the issues of an increasingly tight application schedule and the need for construction vehicles to traffic the membrane shortly after application, and on an on-going basis.
The ability to overcome these potential problems resulted in the Eliminator® waterproofing system being specified for the new bridge deck. Following a competitive tender the FCI-Cleveland Joint Venture awarded the contract to apply the Eliminator® system to the 26,500m² (285,000 square foot) deck to Venture Construction of New Hampshire, one of Stirling Lloyd’s authorised applicators in the USA. The waterproofing of the deck was undertaken in three phases, with the first beginning in May 2003. This involved the waterproofing of the edgworks, upstands and the deck area on which the concrete crash barrier, separating the cycle/pedestrian lane from the main deck, would be cast.
> Next
|
|
|
