1. the transverse bending stiffness and torsional stiffness of U-shaped section are better than those of other sections;  

2. the upper part of the U-shaped side plate has a large tensile stress, which improves the stability coefficient of the side plate; 

3. U-shaped bottom plate can improve the ability of resisting local instability;  

4. in the case of the same lifting performance, the lifting arm of U-shaped section reduces the weight of the lifting arm and improves the lifting performance of the automobile crane;  

5. the U-section telescopic arm has smaller stress and better stress distribution at the socket;  

6. under the same cross-sectional area and the same force, the U-section lifting arm greatly improves its anti-deformation ability.