Door scaffolding is a kind of multi-functional scaffolding, mainly composed of door frame, cross frame, cross support bar, pins, hanging mouth scaffold and articulation bar and other components. Because the main frame is "door" type, so called door scaffolding. Door scaffolding can be used not only as internal and external scaffolding for building construction, but also as floor, beam formwork support and mobile scaffolding, etc. It has more functions, so it is also called multi-functional H frame scaffolding.

The structural stability of the H scaffold is an important element of the structural safety of the project, and is also a prerequisite for ensuring the safe operation of construction personnel. Usually the onset of the accident is due to the instability of the scaffolding structure, and the main reasons for the onset of instability are: defects in the structure of the frame itself; lack of wall ties set up, with wall pieces of stiffness is not enough; horizontal reinforcement rod or scissor brace is not set up enough; not enough understanding of the material properties of steel pipe, improper mixing of different wall thickness steel pipe; load consideration is not enough, the stability of the calculation is wrong; construction Management is not in place. According to the scope of its onset can be divided into the entire structure or part of instability, individual component instability and component of the local instability; and can be divided into in-plane and out-of-plane instability. Sometimes in the elastic range without the onset of buckling, but in the full section before the arrival of plastic onset of elastic-plastic buckling, so it can also be divided into elastic stability, elastic-plastic stability and plastic stability. Any kind of instability phenomenon may make the structure can not work effectively.