Effect of Joint Stiffness of Back Web Members on the Dynamic Characteristics of "П" Type Oil-Drilling Mast

The effect of the joint stiffness of back web members on the dynamic characteristics of the mast system for oil drilling is investigated by analyzing a real mast of the type ZJ20. The dynamic characteristics of the mast system with three types of joints, i.e.,pin joints, cardan joints and fixed ends, of the back web members are investigated, and the first six modes and natural frequencies are given. It has brought to light that as the joint stiffness is changed between the extremes, the first six modes and the natural frequencies can have deviations of 27%～48% off their average .