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The Skyway Roadway
The Skyway will have 452 separate roadway segments, most of them 25 feet long, three stories high, 90 feet wide and weighing between 480 and 780 tons. The placement of these giant, precast blocks in shifting winds and tides is a construction feat of the first magnitude, requiring precision engineering and highly skilled workers. Here's how they'll do it:
The roadway construction starts at the top of each column. Above the water, the first road deck sections, called pier tables, will be cast in place as opposed to being precast in the Stockton yard like the other sections and barged to the site.
The pier tables, like the rest of the road deck sections, are essentially chambered boxes topped with overhanging road deck and diagonal panels called wings.
Within the precast sections will be 4.5-inch galvanized tubing ducts for the miles of steel cables that will help support the bridge. Also within these chambers and the central core will be water and sewage lines serving Yerba Buena Island, as well as power lines and two electrical substations feeding the bridge.
Once a table pier has been formed and has cured, the falsework used to construct the piers will be removed and the construction of the roadway out from the piers will begin. Crews will work in a westward direction, starting with the eastbound roadway piers.
First, pairs of special "sleds" will be mounted atop each pier table with plates and tension bars. The role of these giant, 800-ton-capacity rigs is to raise the Skyway sections into place. Each sled will have a work platform at its far end and arms extending over the water.
These winch cables will attach to the roadway sections at four points. Each cable can be adjusted up to four feet to compensate for pitch, yaw and other movement of the roadway section. This is critical, since these 480- to 780-ton sections will sometimes be raised in choppy, windy conditions.
When the roadway section is raised to within approximately six inches of its position, the joining faces of roadway will be coated with a sixteenth of an inch of high-strength, slow-curing epoxy. In addition to holding the bridge together, the epoxy will help seal the joints from moisture, preventing corrosion to metal components in the chambers below. Alignment keys formed into the sections at the precast yard will help line up and secure the sections.
In addition, a series of tension rods will be installed to tightly connect the roadway to the section atop the column. The rods will be snugged tight by jacks and rams.
Each roadway section will have six lengthwise tendons composed of 37 separate half-inch steel strands, each capable of sustaining 270,000 pounds of force. A specially-designed anchor system will keep the tendons in place as the next roadway section is hauled into position.
A four-strand transverse tendon will run every two feet across the bridge. In all, some 5,000 miles of steel cable strands will course through the bridge, their channels eventually filled with grout.
One of the biggest challenges facing KFM and Caltrans is to maintain "geometry control," meaning the proper alignment of the bridge sections as construction progresses. Each time a section is attached, that portion of roadway will move a bit as the concrete shrinks and expands. Because they have been cast in place, the pier tables will be more subject to distortion as they cure than the precast sections, a possibility engineers will have to constantly monitor. To ensure proper alignment, KFM surveying crews will take daily readings.
Crews will also install four unique safety hinges on the bridge. These structures consist of 6-foot-diameter, 60-foot-long, 4-inch-thick steel pipes placed inside stainless steel sleeves. These are in addition to smaller expansion joint assemblies that will be installed at 14 section joints.
In the event of an earthquake or when temperature changes cause shrinkage or expansion, the pipes slide inside their sleeves, relieving pressure on the bridge and preventing damage. Caltrans is also installing a seismic monitoring system at key locations to indicate forces and displacements caused by an earthquake.
This process of lifting, gluing and cabling the Skyway sections will continue until the advancing roadways nearly meet in the middle of each span. A six-foot gap left in the middle of each crossing will be closed with a concrete pour.
The roadway sections will be match-cast in Stockton to assure a smooth surface transition. Once all the sections are in place, a 2-inch layer of polyester concrete will be applied as a top surface.
The end of the Skyway where it will attach to the Suspension Section will have a steel nose designed to connect with the adjoining structure. On the Oakland side, the Skyway will connect to the Oakland Touchdown .
After the roadway is complete, the steel bicycle and pedestrian path will be attached with cantilevers to the south side of the eastbound deck, and lighting and other features will be installed.