Tower crane boom: The cross section of crane boom is isosceles triangle. Top chord, tilted belly poles and horizontal tilted belly poles are all seamless steel tubes. Two bottom chords are made of steel bars. Make sure the surface and side of bottom chords smooth and mutually vertical so that they can also be used as operation track of trolley. The crane boom consists of eight joints and there is no interchangeability between each joint. According to its structure features and joint method of top chord, installation position of each boom could be located. Top chords of each joint are connected by flanges and four M22 high-strength bolts and bottom chords by plugged pins. With little gap, the joint is smooth so as to reduce vibration when small wheels pass.