【正文】 erse steel had to be determined for use in the plastic regions of the shaftthat is, those at the top oneeighth of eighth of each shaft and within the shaft caps, which would absorb the highest seismic demands. Once this amount was determined, it was used as the minimum for areas of the shafts above their points of fixity where large lateral displacements were expected to occur. The locations of the transverse steel were then established by following code requirements and by considering the construction limitations of CIDH piles. The transverse steel was spiral shaped. Even though thief foundation designs differed, the towers themselves were designed to be identical. Each measures m from the top of its pile cap and is designed as a hollow reinforcedconcrete shaft with a truncated elliptical cross section (see figure opposite). Each tower’s width in plan varies along its height, narrowing uniformly from m at the base of the tower to 6 m at the top. In the longitudinal direction, each pylon tapers from m at the base to about 8 m right below the deck level, which is about 87 m above the tower base. Above the deck level the tower’s sections vary from m just above the deck to m at the top. Each tower was designed with a 2 by 4 m opening for pedestrian passage along the deck, a design challenge requiring careful detailing. The towers were designed in a accordance with the latest provisions of the ATC earthquake design manual mentioned previously (ATC32). Owing to the portal frame action along the bridge’s longitudinal axis, special seismic detailing was implemented in regions with the potential to develop plastic hinges in the event of seismic activityspecifically, just below the deck and above the footing. Special confining forces and alternating open stirrupswith 90 and 135 degree hookswithin the perimeter of the tower shaft. In the transverse direction, the tower behaves like a cantilever, requiring concreteconfining steel at its base. Special attention was needed at the joint between the tower and the deck because of the centralplane staycable arrangement, it was necessary to provide sufficient torsional stiffness and special detailing at the piertodeck intersection. This intersection is highly congested with vertical reinforcing steel, the closely spaced confining stirrups of the tower shaft, and the deck prestressing and reinforcement. The approach structures on either side of the main span are supported on hollow reinforcedconcrete piers that measure by 5 m in plan. The design and detailing of the piers are consistent with the latest versions of the ATC and AASHTO specifications for seismic design. Capacity design concepts were applied to the design of the piers. This approach required the use of seismic modeling with moment curvature elements to capture the inelastic behavior of elements during seismic excitation. Pushover analyses of the piers were performed to calculate the displacement capacity of the piers and to pare them with the deformations puted in the seismic timehistory analyses. To ensure an adequate ductility of the piersan essential feature of the capacity design approachit was necessary to provide adequate concreteconfining steel at those locations within the pier bases where plastic hinges are expected to form. The deck of the cablestayed main span is posed of singlecell box girders of castinplace concrete with internal, inclined steel struts and transverse posttensioned ribs, or stiffening beams, toward the tops. Each box girder segment is m deep and 6 m long. To facilitate construction and enhance the bridge’s elegant design, similar sizes were used for the other bridge spans. An integral concrete overlay with a thickness of 350 mm was installed instead of an applied concrete overlay on the deck. In contrast to an applied overlay, the integral overlay was cast along with each segment during the deck erection. Diamond grinding equipment was used to obtain the desired surface profile and required smoothness. The minimum grinding depth was 5 mm. A total of 128 stay cables were used, the largest prising 83 monostrands. All cables with a length of more than 80 m were equipped at their lower ends with internal hydraulic dampers. Corrosion protection for the monostrands involved galvanization of the wires through hot dipping, a tight highdensity polyethylene (HDPE) sheath extruded onto each strand, and a special type of petroleum wax that fills all of the voids between the wires. The stays are spaecd every 6 m and are arranged in a fan are designed to be stressed from the tower only and are anchored in line with a continuous stiffening beam at the centerline of the deck anchorage system is actually a posite steel frame that encapsulates two continous steel plates that anchor the stays and transfer the stay forces in a continuous and repetitive systemvia shear studsthrouthout the extent of the cablesupported deck (see figure above).A steel frame was designed to transfer the stays’ horizontal forces to the box girders through concreteembedded longitudinal steel plates and to transfer the boxes’ vertical forces directly through the internal steel innovative and elegant load transfer system made rapid construction of the concrete deck segmentsin cycles of three to five dayspossible. In addition to the geotechnical and seismic analy