(Continuation of the previous period) ② The column with the extension arm (7, 6, 5 and 5 ', 6 ', 7 ') is installed with two pairs of hoists at the same time, and the lifting arm is turned in the center after the volleys. Move the lift forward to the installation node, and then slowly loosen the auxiliary lifting point to make the member turn over and vertical, and then install in place, as shown in Figure 26a), b), c).