土木工程橋梁外文翻譯--跨越世紀之橋(編輯修改稿)

　

【文章內容簡介】 portionally distributed to the towers and the piers by the fixity of the deck to the towers and by reinforcedconcrete shear keys located at the top of P1, P3, and P4. The deck is allowed to move longitudinally over the abutments and piers. The longitudinal, seismic, live, and temperature loads are absorbed by what is known as portal frame structural behavior, whereby the towers and the deck form a portalmuch like the frame of a door in a buildingthat acts in proportion to the relative stiffness of the two towers. As previously mentioned, the presence of petent basalt on the east side of the site meant that shallow foundations could be used there。 in particular, spread footings were designed for the east tower, the east approach structure, and the east abutment. The west tower, the west approach structure, and the western piers (P2 and P3), however, had to be founded deep within the Cucaracha Formation. A total of 48 castindrilledhole (CIDH) shafts with 2 m outer diameters and lengths ranging from 25 to 35 m were required. A moment curvature analysis was performed to determine the capacity of the shafts with different amounts of longitudinal steel rebar. The results were plotted against the demands, and on the basis of the results the amount of required longitudinal reinforcing steel was determined to be 1 percent of the amount of concrete used in the shafts. The distribution of the longitudinal reinforcing steel was established by following code requirements, with consideration also given to the limitations of constructing CIDH piles with the contractor’s preferred method, which is the water or slurry displacement method. A minimum amount of transverse 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 integ