六十年代以来,国际上预应力混凝土桥梁以钢绞线为预应力筋束的张拉体系有所发展,随着大型现代化桥梁的增多,这种张拉体系越来越广泛地被采用,而以钢丝为预应力筋束的张拉体系已不能适应桥梁发展的需要。如美、英、意等许多国家,在预应力混凝土桥梁结构中,钢绞线已成为一种主要的预应力筋材料。 Since the 1960s, the tension system of prestressed concrete bridges in the world with strand as prestress tendons has been developed. With the increase of large modern bridges, the tension system is more and more widely adopted. However, The prestressing tendons tendons to the tension system can not meet the needs of bridge development. Such as the United States, Britain, Italy and many other countries, in the prestressed concrete bridge structure, the strand has become a major prestressed tendons material.