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中文字数:4215,中文页数:4 英文字数:2842页数:5
Prestressed concrete has been used extensively in U.S. bridge construction since its first introduction from Europe in the late 1940s. Literally thousands of highway bridges of both precast, prestressed concrete and cast-in-place post-tensioned concrete have been constructed in the United States. Railroad bridges utilizing prestressed concrete have become common as well. The use and evolution of prestressed concrete bridges is expected to continue in the years ahead.
Short-span Bridge
Short-span Bridge, as shown in Fig.18.1 for the purposes of this discussion, will be assumed to have a maximum span of 45ft (13.7m). It should be understood that this is an arbitrary figure, and there is no definite line of demarcation between short, moderate, and long spans in highly bridges. Short-span bridges are most efficiently made of precast prestressed-concrete hollow slabs, I-beams, solid slabs or cast-place solid slabs, and T-beams of relatively generous proportions.
19世纪40年代后期，预应力混凝土首次引入美国，很快便广泛应用于桥梁结构中。据记载，美国建筑了数千座预应力混凝土公路桥。铁路桥利用预应力混凝土也很普遍。在未来的几年中，预应力混凝土桥有望继续使用和不断向前发展。
短跨桥
如图18.1所示的短跨桥，最大跨径为45ft．要知道，这是一个武断的说法，短跨桥，中等跨度桥和大跨桥没有严格界限。短跨桥多由先张法预应力混凝土空心板，I字梁，实心板，或现浇实心板及具有相当比例的T形梁组成。
在很短的跨径上用预制实心板最经济。这种板可以做成任意合适的宽度，但通常是3或4ft.预制构件径向连接通常是关键，在板拼装完后，在接缝处浇筑混凝土使得相邻板件共同承受活载剪力。
