Tower crane is a kind of lifting machine that can realize heavy load transportation. The working height is generally from several tens to hundreds of meters, and the working radius can reach several tens of meters. Currently widely used in construction sites, mainly for the vertical and horizontal transportation of materials in building construction and the installation of building components.

In recent years, according to the relevant General Administration of Quality Supervision and Inspection accident statistics, the crane accident rate and the number of casualties caused by accidents in the eight categories of special equipment always ranked top. In the face of the increasing number of tower cranes, the distribution area is wide and mixed, bringing inconvenience to supervision, the safety devices of tower cranes are map fast, map more provincial users intentionally or unintentionally ignored, bringing many safety hazards to daily production. Here, the author analyzes the eight common safety hazards of using tower cranes in construction sites, as follows:
1. Torque limiter failure

The failure of the torque limiter mainly includes the failure of the elastic deformation of the arch frame and the failure of the electric contact switch of the torque limiter.

The deformation failure of the arch frame causes the tower crane to be overloaded, but the deformation of the arch frame cannot reach the electric contact switch, so as to achieve the purpose of overloading without alarm. There are two forms:The arch frame is fixed with wire, and the arch frame is deformed for a long time.

Torque limiter touch switch failure is electrical components damage, long exposure, no rain cover protection, resulting in corrosion and aging failure.

Another failure mode is the reverse installation of the adjusting screw, that is, the direction of the adjusting screw nut is opposite to the direction of the electric touch switch installation.

2. Lifting weight limiter failure

The failure of the lifting limiter ties the sensor pin of the lifting limiter and the crossbar at the root of the boom together with wire, making the tower crane. Impossible to limit the lifting load to prevent overload operation, will cause damage to the lifting drive part and the corresponding structure, motor, electrical.

3. luffing trolley fall protection rope failure

The tower crane safety regulations GB5144 provides for the luffing trolley stop rope device stop rope rod

Or block rope plate and the outer edge of the sheave clearance shall not exceed 20% of the diameter of the wire rope, luffing trolley use process, luffing wire rope in the impact is easy to jump out of the sheave groove, resulting in block rope plate or block rope rod fracture, lose anti-falling rope effect. See Figure 4.

4. Variable amplitude mechanism amplitude limit failure

The amplitude limiter of the luffing mechanism is a safety device to prevent the trolley from colliding with the two ends of the boom and an accident. I

Installed in the trolley traction winch reel. The failure of the amplitude limit is mostly when the trolley is near the root of the boom, the limit within the limit short-circuit when adding the tower body, and the limit is not restored after adding the tower machine.

5. Lifting height limiter failure

Lifting height limiter is to prevent the hook from rising above the limit position, so that the winch can break the wire rope, causing the lifting weight to fall.

Accident safety device. The main reason is the height limiter short circuit when adding the tower, forget to restore the height limiter after adding.

6. Tower height and strength bolts loose

High-strength bolts are important parts connecting various parts of the tower, tower cranes in the use of the process is easy to loosen, need to tighten often.

Loose situation is as follows, but some human factors, such as the connection bolt between the tower body and the slewing mechanism, deliberately not tightened to facilitate the next lifting of the tower body.

7. Tower crane attached wall

When the tower crane exceeds its independent height use, need to set additional wall to the tower crane for reinforcement. Attachment wall reinforcement is characterized by tensile and compressive forces.

Currently some construction sites use the attached wall bar directly welded with the wall pre-built steel plate, no attached wall stress calculation sheet, so regardless of the length of the attached wall, only steel connection.