外文翻译--斜拉桥的未来

中文 1590字 between towers increase if the number of cables increase and the angle of inclination of the cables remains the same. B.READING MATERIAL FUTURE OF CABLE-STAYED BRIDGES I would like to begin with a view back on the development of cable-stayed bridges during the last 25 years.It started with Dischingers publication shortly after the end of Word War II. He pointed mainly to the necessity of gonging to high steel stresses in the stays to produce stiffness in the system.The first bridge following Dischingers recommendations,was built in Sweden,designed by Demag,a German steel construction firm,consulted by Dischinger. Then in 1953-54 the three Duesseldorf bridges were designed,all of them,with parallel stay cables but different tower arrangements,in order to have a family of similarly appearing bridges. The fundamental concept of these early designs was retained for over almost 20 years,which it took to built them. We learned by detailing and erecting these bridges. In these bridges,only a few stay cables were chosen;some engineers designed their bridges with even only one stay cable. This resulted in large cable forces causing difficulties to anchor the cables in the beam structure. Heavy cross beams were necessary, the ropes had to be formed. To gain sufficient space for the anchors, adjustment of cable lengths becomes difficult. In addition, the large distance between the stay cables complicate the erection requiring heavy equipment, auxiliary trusses,even auxiliary piers were necessary to build the Maracaibo bridge and the Kniebridge. Auxiliary stayes were needed for cantilevering the beam plate girder to the next stay cable. In addition, long spans between supports provided by stay cables,cause large bending moments in the continuous beam and hereby a considerable depth of the girders is needed. Form all of this experience, we concluded for our later and future designs ,that a) a large number of stay cables should be chosen in a way b) that one anchorage socket can be used to simplify the placing of the cable, c) by short spacing of the cables, bridge girder bending moments are low so that a depth of 1 to 2 m is sufficient, just providing a deflection line curvature satisfying traffic requirements and providing safety against buckling in the deflected stage. d) The spacing of the cables should be such, that no heavy erection equipment is needed to cantilever out for placing the next following stay cable. e) Feasible spacings may be between 6 and 12 m for concrete girders and between 8 and 16 m for steel girders. In order to satisfy these rules, my office developed a new type of cable anchorage in cooperation with BBR Switzerland, which allows ultimate cable forces up to almost 2,000 tons, using parallel wires or strands of very high strength, inside a polyethylene tube for perfect corrosion protection. The anchorage was developed to get high fatique strength, therefore called High Amplitude(HiAm) cable. These cables can be prefabricated and shipped on reels and allow a simple and inexpensive erection. Several bridges have been designed lately using these principles:The Pasco bridge, bridges in Parana, Argentina, and others. As we designed these bridges, I knew already the favorable effect of system damping in multi-stay cable bridges by experience which I had gained from the behavior of a pedestrian stay cable bridge in Stuttgart, but we had to prove the dynamic safety for these larges. A dynamic model test was made at the Ismes Institute of Profssor Oberti in Italy, 18 m long designed for full dynamic similitude. Short and long trains or just locomotives could run on the rails with different speeds-no adverse oscillations could be detected. Then the test engineers excited artificially oscillations going through all possible modes and frequencies and at many points of the bridge. Whenever they succeed in building up a small amplitude, it broke quickly again down to small amplitudes. It was impossible to find a mode of oscillation which would build up large amplitudes by resonance. Any mode of oscillation broke down as soon as the amplitudes starts to grow, because each of the cables has a different natural frequency and disturbs the oscillation of deck structure by interference so strongly, that large amplitudes cannot develop. We get a very effective system damping which does not allow resonance oscillation with dangerous amplitudes. Of course, this effect is only obtained with stiff and highly stressed cables and with a sufficient number of cables in close spacing. We must recognize that the dynamic behavior of the suspension bridge is perfectly different from that of a multi stay cabled bridge. In s suspension bridge without stiffening girder, there is full freedom for the dangerous first antimetric mode of oscillation, combining torsional and bending movement. Small force can excite this mode of oscillation and build up large amplitudes by resonance. These oscillations can be restrained by stiffening trusses with large bending and torsional rigidity and resonance can mainly be avoided by a large difference between the natural frequencies of bending and torsional oscillations. Sectional mode tests in wind tunnels and theories have been well developed for these suspension bridge problems. The multi stay cable bridge-on the other side-cannot oscillate in low order modes, it especially cannot move into combined torsional and flexural oscillations. With stays along the edges of the bridge, torsional oscillations are almost impossible and flexural oscillations assume quickly high order modes with only small amplitudes. The important fact is,that resonance is impossible for the reasons described. As a consequence, we must learn that the theories which were developed to check aerodynamic safety of suspension bridges are not valid for multi stay cabled bridges. Wind tunnel tests with sectional models must be made with realistic restraint by system damping which, however, is difficult to imitate for a sectional model. * * * Fritz Leonhardt, Dr. Ing. Stuttgart, Germany 斜拉桥的未来 我想先简单回顾一下在过去 25年间斜拉桥发展历史，二战结束后不久，迪斯钦格便在其著作中提出了斜拉桥这一概念。在著作中，迪斯钦格主要指出，在斜拉桥这个系统中，支索上所承受的巨大钢筋压力对维持桥的稳定性有重要作用。第一座依据迪斯钦格的建议建立的斜拉桥位于瑞典。这座桥是由德国一家名为德马格的钢铁建筑公司设计的，而这家公司正是由迪斯钦格担任指导。 然后在 1953-1954年间，共有 3座杜塞尔多夫桥相继建成。这 3座桥全部都是平行的钢筋支索。但支柱的设计却各不相同。这样做的目的是为了建造一个拥有相似造型的 桥梁群。 在将近 20年的时间里，桥梁建设一直都是在应用这些早期的基本设计理念。我们通过研究这些桥梁的细节部位和建造桥梁模型来学习这些理念。 这些桥只选择了几根钢缆，一些工程师设计的桥甚至只有一根钢缆。这跟钢缆在横梁结构的桥上的固定造成巨大缆绳压力。沉重的交叉横梁是必要的，绳子也是必要的。为了给支柱营造足够的空间，缆绳长度的调整变得困难起来。此外，钢缆之间的巨大空间使得需要沉重设备的建设变得复杂，辅助构架，甚至辅助墩对马拉开波桥和尼克桥的建造都是必要的。将支柱大梁连接到下一个钢缆需要用到辅助支索。此外，钢缆提 供的支撑之间的长墩距造成连续支柱的巨大弯曲，因此，大梁需要有足够的深度。 从所有这些经验我们得出这样的结论，我们今后或未来的设计 A）多数钢缆应该选择这种形式； B）固定处的凹口可简化钢索的排列方法； C)通过缩短钢索的间距，桥梁弯曲几率降低，因此 1到 2米的深度已足够提供一条偏斜直线曲度，并在偏斜阶段保证交通安全； D）排列钢索应切记，桥梁悬臂上不能累加重物以影响接下来钢索的排列； E)可行的混凝土大梁的排列方法是 6米到 12米，而铁梁则需 8米到 16米。 为满足以上要求，我方与瑞士 BBR 公司合作研发出了一种新型斜拉桥，钢索可承重高达两千吨，在聚乙烯钢管中，采用了高强度平行结构金属线以防止腐蚀，新型斜拉桥可承受高压，因此被称为高振幅钢索。这些钢索可提前制造且造法简单，成本低。近期所造的一些大桥均采用了这些准则：毕