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Installation of the new steel girders began in mid-August. This picture is taken at the eastern end of the bridge looking south, showing all the girders installed for Span 17 of the structure. Painted weathering steel was used to help protect against corrosion in the harsh marine environement. The steel girders are more than 6’ deep (tall), and have an average weight of approximately 300 pounds per foot.
This picture shows one of the girders being lifted into place. The girder being lifted in this photo weighs about 35,000 pounds. The girders are shipped to the site by truck directly onto the contractor’s temporary trestle/work platform. Two cranes are then used to lift the girders off the trucks and into their final position. Close coordination between the crane operators and the entire construction crew is required to safely install the girders. Note in the background that there is a section of these girder segments that extend beyond the pier, which is discussed more in the next photo. The girder being lifted in the photo will be connected to the end of one of the girders already installed.
This picture shows iron workers bolting up the steel at a field splice location from a newly installed girder segment to the overhanging segment from a previously installed girder. After the girder is in place, the cranes provide full support until all the bolts are installed. 84 high strength bolts are installed on either side of the connection to develop the strength required, or 168 bolts in total per connection. The field splices are located at locations of minimal stress. Steel lateral bracing can be noticed on top of the far pier to provide temporary resistance to any lateral forces, such as wind, that the lone girder may experience for stability until the next girder and bracing can be erected.
This photo shows the cross frames/diaphragms for the steel girders. After the girders are erected, the diaphragms are placed to provide resistance to horizontal loads and an increase in load sharing between the individual girders. There are a total of 6 girders spaced at 10’-6” for the new WB superstructure. The new steel girders are straight as opposed to the existing girders that were haunched (deeper at the piers) that were used on the existing bridge. To accommodate the reduced steel depth, the existing pier cap seat had to be raised up to seat the girders (the amount the seat was raised can be seen in the different colors of concrete on the face of the pier cap – over time as the concrete ages, this will not be noticeable in the future).
This picture shows the completed east abutment wall that supports the first span of beams and retains the soil from the approach roadway. The abutments for the new bay bridge and rehabilitated bay bridge are now connected to provide complete closure from the approaches. Note that the steel for the rehabilitated bridge was painted to closely match the color of the concrete structure beyond. Steel was used for the rehabilitated bridge because the concrete beams are more than three times heavier than the steel girders, which would have overloaded the original foundations of the rehabilitated bridge which will remain in service.