预应力混凝土在桥梁中应用的初期,设计者都按照自己的意图提出“最好”的主梁截面。这样,每个承包商都得采用外形稍有差异的主梁,使得后来的承包工程无法重复使用原有的主梁形式。因此,制造商很快就感觉到他们负担不起价格昂贵的钢模的经常变换,而每一座桥梁都要按惯例设计一种主梁,其造价也实在太贵了。 Early in the application of prestressed concrete bridge, designers are in accordance with their intentions to put forward the “best” section of the main beam. In this way, each contractor has to adopt a slightly different shape of the main beam, making the subsequent contracting project can not be reused the original form of the main beam. As a result, manufacturers soon felt that they could not afford the often-expensive transformation of expensive steel molds, and that every bridge was traditionally designed with a main beam that was too expensive to manufacture.