预制混凝土柱在吊装前需要测设三面线,用以保证吊装的垂直精度。测设三面线的关键是保证柱子两个侧面中心线的平行。混凝土柱在制做过程中不可避免的会出现一定程度的扭曲,故不能采用分中的方法来测设三面线。过去一般利用大杠或十字架靠人眼穿,来保证两侧面线的平行。随着现代化建筑的不断发展,柱长在10m以上的已很平常,因 Prefabricated concrete columns need to be measured with three lines before lifting to ensure the vertical accuracy of lifting. The key to measuring three lines is to ensure that the two sides of the column are parallel to the center line. The concrete column will inevitably appear a certain degree of distortion in the process of making, so it can not be used to measure the three-sided line. In the past, large bars or crosses were generally worn by human eyes to ensure the parallelism of the two side lines. With the continuous development of modern buildings, it is common for column lengths to exceed 10m.