Bridge Construction Techniques 桥梁施工方法 The final cost of a bridge is the sum of the cost of permanent materials,the proportionate cost to the project of plant and temporary works and the cost of labor .The cost of permanent materials can be estimated reasonably correctly.With experience,a bridge contractor can deal completely with cost of plant and temporary works .But the labor cost does not lend itself to exact analysis .Recent competitive designs have attempted to introduce innovations in construction methods with a view to effect economy in the cost on labor by reducing temporary works and by minimizing the duration of site work. 一座桥梁的最终造价是建造桥梁结构物的材料费用与这项工程相关的机械费用和临时工程及劳动力的费用的总和。材料的费用能够被预算的相当准确的，承包商们借助施工经验是能够估算施工机械和劳动力的费用的。但是劳动力的费用是不能够精确分析的。最近的一项比较有竞争力的设计试图通过减少临时工程和工程的工期来革新施工方法。
The suitable techniques of construction of bridge superstructure will vary from site to site,and will depend on the spans and length of the bridge, type of the bridge,materials used and site conditions. For instance, cast-in-site concrete construction could be adopted for short spans up to 40 m, if the river bed is dry for a considerate portion of the year, whereas free cantilever construction with prestressed concrete decking would be appropriate for long spans in rivers with navigational requirements. The current trend is towards the avoidance of staging as much as possible and to use precast or prefabricated components to maximum extent.Also , construction machinery such as cranes and launching girders are coming into wider use . These are greater savings to be effected by paying attention to the method of construction even from the design stage than by attacking permanent materials . 桥梁上部结构比较适宜的施工方法将随施工场地不同而不同，并主要取决于桥梁的长度和跨度、桥梁的类型、基础条件及其所使用的材料。例如：现场浇注混凝土的施工方法适用于40米以下的短跨径桥梁，如果河床在一年中的大部分时间是干燥的，那么预应力混凝土悬臂施工方法在有通航要求的大跨桥梁中是比较合适的。现在的发展趋势是尽可能避免使用台架施工，而在最大程度上采用预制构件；另一方面，起重机、滑拽梁等施工机械的应用范围也越来越广。这些都是从对施工方法的密切关注甚至是设计过程的密切关注而取得的巨大收获，而不是在善于解决永久材料。 Short Span Bridges小跨度桥梁 For bridges involving spans up to 40 m , the superstructure may be built on staging supported on the ground . Alternatively , the girders may be precast for the full span length and erected using launching girders or cranes,if the bridge has many equal spans.In the latter procedure , the additional cost on erection equipment should be less than the saving in the cost of formwork and in the labour cost resulting from faster construction . 当桥梁的跨度小于40米左右时，它的上部结构可以通过支承在地面上的趾甲施工。其它的施工方法中的梁可以整体预制，然后利用顶推梁或起重机架设。如果这座桥梁是等
