大型橋梁及施工外文翻譯--大跨度橋梁-橋梁設(shè)計-展示頁
2025-05-27 04:22本頁面
【正文】 based on sound principles and assumptions, the girder stiffened by inclined cables suffered various misfortunes which regrettably resulted in abandonment of the system. Nevertheless, the system in itself was not at all unsuitable. The solution of the problem had unfortunately been attempted in the wrong way. The renaissance of the cablestayed, however, was finally successfully achieved only 1 during the last decade. Modern cablestayed present a threedimensional system consisting of stiffening girders, transverse and longitudinal bracings, orthotropictype deck and supporting parts such as towers in pression and inclined cables in tension. The important characteristics of such a threedimensional structure is the full participation of the transverse construction in the work of the main longitudinal structure. This means a considerable increase in the moment of inertia of the construction which permits a reduction in the depth of the girders and economy in steel. Long span concrete bridges are usually of posttensioned concrete and constructed either as conditions beams types or as free versatile structures. Many methods have been developed for continuous deck construction. If the clearance between the ground and bottom of the deck is small and the soil is firm, the superstructure can be built on staging. This method is being obsolete. Currently, freecantilever and movable scaffold systems are increasingly used to save time and improve safety. The movable scaffold system employs movable forms stiffened by steel frames. These forms extend one span length and are supported by steel girders which rest on a pier at one end and can be moved from span to span on a second set of auxiliary steel girders. An economical construction technique known as incremental pushlaunching method is developed by BaurLeonhard team. The total continuous deck is subdivided longitudinally into segments of 10 to 30 m length depending on the length of spans and the time available for construction. Each of these segments is constructed immediately behind the abutment of the bridge in steel framed forms, which remain in the same place for concreting all segments .The forms are so designed as to be capable of being moved transversely or rotated on hinges to facilitate easy stripping after sufficient hardening of concrete. At the head of the first segment, a steel nose consisting of a light truss is attached to facilitate reaching of the first and subsequent piers without including a too large can yielder moment during construction . The second and the following segments are concreted directly on the face of the hardened portion and the longitudinal reinforcement can continue across the construction joint . The pushing is achieved by hydraulic jacks which act against the abutment .Since the coefficient of friction of Teflon sliding bearings is only about 2 percent, low capacity hydraulic jacks would suffice to move the bridge even over long lengths of several hundred metres . This method can be used for straight and continuously curved bridges up to a span of about 120 m . The freecantilever system was pioneered by Dyckerhoff and Willmann in Germany .In this system , the superstructure is erected by means of cantilever truc
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