过去预应力只用在大型构件上,预应力筋采用粗钢筋或钢丝(筋)束,千斤顶的张拉吨位只有60吨一种。随着新钢种和新结构的不断出现,预应力的应用范围已普遍的扩大到屋面板、檩条等中小型构件。这些构件中预应力钢筋的直径一般只有12～16毫米,如果再用60吨千斤顶来张拉,不但过分笨重,操作不便,而且准确度差,影响质量。在党 In the past, prestressing was only applied to large components. Prestressed tendons used coarse steel or steel wire (strand) bundles, and the tension tonnage of jacks was only 60 tons. With the continuous emergence of new types of steel and new structures, the application of prestress has been widely expanded to small and medium-sized components such as roof panels and purlins. The diameter of the pre-stressed steel bars in these components is generally only 12 to 16 mm. If 60 ton jacks are used for tensioning, it is not only unwieldy and inconvenient to operate, but also has poor accuracy and affects quality. In the party