Portal scaffold is one of the most widely used scaffolds in construction. Because the main frame is in the shape of “door”, it is called portal or portal scaffold, also known as scaffolding or gantry. This kind of scaffold is mainly composed of main frame, cross frame, interspersed diagonal brace, scaffold board, adjustable base, etc.

Three major causes of accidents caused by portal scaffold

1. Material problems

The materials used for scaffolding and formwork are mainly steel pipes and bamboo poles. According to the standard, the steel pipe used for fastener scaffold shall be welded plain carbon steel pipe with outer diameter of 48mm and wall thickness of 3.5mm. In order to seize the market and compete at a low price, many steel pipe manufacturers consume steel pipes with a wall thickness of 3.0-3.2mm, which is still calculated according to the theoretical weight of 3.5mm when settling accounts with users. The practical weight of each ton of steel pipe is 860-920kg. Because the steel pipe rental is priced by length, not by weight, the rental unit is still willing to buy low price steel pipes with wall thickness of 3.0-3.2mm. However, the moment of inertia of this kind of steel pipe is about 10%. Assuming that after many years of construction and use, the steel pipe corrosion will make the wall thickness thinner, and the moment of inertia of the steel pipe will also be reduced. Therefore, these steel pipes will be a danger to the safety of the scaffold in the future.

2. Planning issues

The main reason for the collapse of scaffold and formwork is the instability of support, because many construction enterprises do not stop the template planning and stiffness checking before the construction of formwork engineering. They just stop the layout of support system, which makes the stiffness and stability of support system lack of consideration. In addition, in the planning and accounting of the formwork support system or scaffold, the hinged joint of the steel structure is selected for the accounting sketch, and the members are connected at one point, while the steel pipe is connected by fasteners, and the steel pipe is subjected to eccentric load. Therefore, there is a considerable gap between the field practice and the planning and accounting. Some steel pipe materials are severely corroded or worn, and some parts are bent or open welded, which can reduce the load of steel pipe in practice. In the case of lax site management, the instability of formwork support is easy to occur.

3. Use problems

At present, there are many skilled workers in the construction site who do not give detailed safety skills disclosure to the operators. In addition, some workers are poor in nature, so it is inevitable to have use problems. For example, some formwork collapse accidents are caused by the operator’s failure to set the distance between shear braces or vertical and horizontal pull rods according to the plan, which leads to the lack of formwork stability; some accidents are caused by the worker’s private withdrawal of the connecting pull rod between the external scaffold and the building, which leads to the collapse of the whole scaffold; Other accidents are concentrated accumulation of construction materials, prefabricated components or construction equipment on scaffolds and formwork, resulting in instability of component members and collapse of the whole. Therefore, the construction site management disorder, the operator did not seriously request the equipment and remove the support according to the plan, which is also an important reason for the collapse accident.