求翻译：是结构受力和构造最简单的桥型，属于静定结构，在目前中小跨径公路桥梁或城市桥梁中应用广泛。混凝土简支梁按建筑材料分为钢筋混凝土简支梁、预应力混凝土简支梁和部分预应力混凝土简支梁等若干类。这几类桥梁具有能就地取材、工业化施工耐久性好、适应性强、整体性好以及美观等许多优点。预应力混凝土梁桥更兼有节省钢材和跨越能力大的长处。那么简支梁桥的最大跨径可做到多少，实际上简支梁桥的设计主要受跨中正弯矩的控制，钢筋混凝土简支梁的经济合理跨径在20m以下，预应力混凝土简支梁的合理跨径一般不超过50m，我国目前预应力简支粱的标准设计最大跨径为40m是什么意思？

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It is the force structure and the construction of the bridge the most simple type of silence, a structure, in the current small and medium-sized cross-trails or roads and bridges in bridge city wide range of applications. Concrete Charpy reinforced concrete as building materials for Charpy, prestres

The bridge is the most simple structures and structure of the force, belong to the static structure, at present small and medium%