Purlins are small in cross section and light in weight. They are hoisted by means of multi-hook hoisting or piece hoisting. The correction of purlin is mainly spacing size and flatness of purlin itself. Spacing checking is done by moving the sample rod back and forth along purlin rods. If there is any error, loosen or tighten the bolts to correct it. Flatness is checked and corrected by drawing wires and steel rulers, and finally fixed by bolts.
