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What are the causes of frequent tower crane collapse accidents?

With the development of the city, more and more high-rise buildings have sprung up, which is inseparable from the hard work of construction workers. However, in recent years, construction accidents have occurred frequently, and there is a price of blood behind almost every building. In the process of building construction, tower crane is the most prone to safety accidents, and the main reasons for frequent collapse accidents of tower crane can be summarized as overload, oblique hanging, weak foundation and other factors. To prevent tower crane accidents, it is necessary to correctly understand the hidden dangers of tower crane operation, strictly abide by relevant safety requirements during operation, and do a good job of inspection before tower crane installation and disassembly.

Cause of tower crane collapse 1 installation and disassembly 1. The installation and disassembly team is unqualified and undertakes the disassembly task without a license. The personnel, equipment and technology of the installation and disassembly unit do not meet the requirements, which is an important cause of the accident.

2. There is no installation and disassembly scheme, and there is no safety technical disclosure, based on experience. The direct cause of the accident is that the demolition unit did not prepare the demolition plan, did not make safety technical disclosure, and acted recklessly in violation of regulations by experience.

3. Dismantling procedures are violated during installation and disassembly. Dismantling units do not dismantle the tower crane according to the disassembly sequence in the instruction manual, and do not operate according to the disassembly scheme and safety technical disclosure requirements, so as to save trouble and rely on imagination.

4. Dismantling and acceptance formalities are not handled. Tower crane users and dismantling units failed to go through the dismantling application and acceptance procedures as required, thus losing the opportunity of inspection by government departments.

2 Usage and operator, operator

1, the operating commander is undocumented. Tower crane drivers and commanders did not receive professional training to obtain qualification certificates as required, and did not have corresponding professional skills and knowledge.

2, operation and command personnel illegal operation, illegal command. Such as overload lifting, oblique lifting, and random turning of concrete pump delivery pipe with tower crane at the construction site.

3, the operator's daily inspection and maintenance of equipment is not enough, resulting in mechanical safety hazards of tower crane. If we don't know enough about the performance of the tower crane torque limiter, we don't know whether it really works, which leads to misunderstanding that it works normally and leads to accidents. Ignore human factors, such as in what range, how much can be hoisted, bottomless or unclear.

4. Insufficient education and training for operators and commanders. Many units only do pre-job training, ignoring the continuous training and improvement of operating skills and safety awareness of operators and commanders.

operational approach

1, overload: tower crane manufacturers often design a certain degree of theoretical overload to meet the actual requirements of construction work, but it also provides some lucky people with opportunities to save money. In fact, different types of tower cranes are usually controlled by lifting torque. When the working range increases or the weight exceeds the corresponding rated load, the overturning moment of the weight exceeds its stable moment, which may lead to the collapse of the tower crane.

2. Inclined crane: In some windy and complicated situations, tower crane drivers often use inclined crane to transport materials that need to be hoisted urgently, but this is a very dangerous behavior. Inclined lifting of heavy objects will increase its overturning moment, generate horizontal and vertical components at the lifting point, and generate additional overturning moment at the supporting point at the bottom of the tower crane, thus reducing the stability factor and causing the tower crane to collapse.

3. Weak foundation: The tower crane has to bear not only its own gravity but also the pressure brought by heavy objects when lifting, so the uneven foundation of the tower crane and insufficient ground bearing capacity are also important reasons for the collapse.

In the case of uneven foundation, excessive verticality error will increase the overturning moment of tower crane and reduce its stability. In addition, the tower crane is erected on soft soil and loose soil. Due to the lack of ground endurance, especially when lifting heavy objects, it can't bear the load, which will lead to loose soil and overturning of the car body.

3 tower crane product quality problem 1, design problem. The design of torque limiter has defects and poor sensitivity; The stress of steel structure design is unreasonable, and the design of hydraulic system is flawed.

2. spare parts. The quality of torque limiter components and the material of steel for steel structure; Quality problems of hydraulic system components and so on.

3. Manufacturing problems

The welding of steel structure can't meet the requirements. The weld height is not enough, and there are defects such as blowhole, slag inclusion and even virtual welding, especially the welding quality problems of important connecting parts such as tower cap, suspender and balance arm.

The geometric dimensions of the steel structure do not meet the requirements. The blanking does not meet the requirements, and the section size of steel can not meet the national standard.

4, the factory certificate and instructions, no factory certificate, is fake and shoddy products. There is no batch description, and the changes to the original design are not marked.

How to prevent tower crane collapse 1 inspection of hidden dangers in tower crane operation 1? Always check and tighten the bolts of the frame part of the tower crane.

2. It is forbidden to lift overweight things, which is stated in the instructions of the tower crane. The weight that the roots and ends of tower cranes can safely lift is generally several times worse, so it must not be taken lightly.

3, often check the limit of tower crane, namely the weight limit. This is the insurance for the tower crane. If the thing to be hoisted is overweight, the tower crane will stop working.

4, tower crane foundation to do maintenance, drainage, avoid water soaking for a long time, cause the tower crane foundation is loose.

5. There are two wire ropes of tower crane, which should be checked every day. Once the wire rope appears burr, it should be replaced immediately, and there must be no luck, otherwise the consequences may be very serious.

6. It is forbidden to buy, lease and use tower cranes with unqualified safety performance and incomplete safety devices, and it is forbidden to illegally use dismantling teams and personnel without qualifications and operation certificates to carry out illegal and risky operations.

Two inspection points before installation of tower crane 1. Whether the tower crane meets the market access conditions (check the registration number): if the tower crane has reached its service life or has potential safety hazards, it should be banned; Tower cranes are backward and outdated products and should be banned.

2. Whether the demolition unit and relevant personnel have relevant qualifications and hold relevant certificates (check the information): the demolition unit should have the professional contracting qualification of lifting equipment installation engineering and the safety production license of the construction enterprise; Dismantling personnel shall be qualified for dismantling and hold relevant certificates.

3. Whether the demolition plan has been made (information check and site inspection): whether there is a targeted demolition plan and it has been approved by the chief engineer and chief supervision engineer of the employing unit; Whether the foundation positioning is reasonable:

First, whether the foundation is located in dangerous parts such as foundation slope.

The second is whether there are practical safety measures to prevent external power supply, and it is strictly forbidden to use high-voltage lines to do unprotected work within the radius of gyration.

Third, whether the anti-collision measures are reasonable: whether the distance between any two tower cranes is more than 2m, whether the boom directly collides with the standard section of the other tower crane, and whether the tower crane with obstacles interfering with the tower crane within the revolving radius of multi-tower operation has approved anti-collision measures.

3. Check point 1 during the installation and disassembly of tower crane, and perform the installation and disassembly notification procedures. Installation and disassembly are not allowed without authorization.

2. Before installation, whether the strength of foundation concrete reaches the design standard value, whether the foundation is concealed and accepted, and whether the foundation bearing capacity meets the specification requirements, the relevant departments shall review the acceptance report.

3. Whether the qualifications and qualifications of on-site dismantling units and dismantling personnel meet the notification procedures.

4. Whether the on-site safety protection work and related personnel are in place and whether the disclosure has been made: whether the management personnel of the dismantling unit are on duty; Whether a warning zone is set up at the dismantling site, and a special person is responsible for safety work; Whether the dismantlers are equipped with safety protection articles as required; Whether the equipment management personnel and site supervisors of the construction unit go to the site for inspection and supervision; Whether the disassembly procedure meets the requirements of disassembly plan and specification.

4. Inspection key points during tower crane construction: 1, whether it has passed the inspection and joint acceptance.

2, tower crane foundation drainage is clear.

3, on-site operation of the driver, the conductor is related certificates, safety education, safety technical disclosure is implemented, whether can special plane, and have a hand-over record.

4. Whether safety measures such as anti-collision and electrical protection for multi-tower operation are put in place, and whether there are unsafe behaviors such as multi-head command and illegal operation.

5, construction, leasing, supervision and other units whether the tower crane for regular inspection, and inspection and maintenance records.

6. For the physical aspects of tower crane, we should pay attention to the following main safety hazards: torque limit, superelevation limit, amplitude limit, slewing limit, hook insurance, wire rope winding, trolley rope breaking and other safety devices, wall-attached devices, bolt pins connecting fasteners, and whether the main stress components are deformed or cracked, whether the welding parts fall off, and whether the broken wires and strands of wire rope meet the scrapping standards.

7. Whether there are related documents and disclosure records such as wall attachment and jack-up during use, especially whether there are any irregularities such as extending the wall attachment or making it without authorization.

Tower crane installation standard process 1, to conduct a comprehensive inspection of tower crane, eliminate all unsafe hidden dangers. Check spare parts.

2. Assemble the components of the tower crane according to the requirements of the tower crane manual.

3. Lift the jack-up jacket and insert it into the foundation section;

4. Install the slewing bearing seat and hang the bearing seat on the foundation part. If the jack-up jacket is correctly positioned, the foot of the slewing bearing seat can be connected with the jacket column (the jacket column can be adjusted with a crowbar). Or, insert the base of the slewing bearing seat into the fishplate of the foundation joint and connect it with a 4×2 pin, then lift the sleeve frame and connect it with the slewing bearing seat with a pin.

5. Install the tower cap, lift it and put it on the bearing seat. C50 15 tower crane is connected by 2×2 pins and 2×8 bolts.

6. Install the balance arm in place and connect it with the tower cap with 2× 1 pin; Then, with the help of the tower top, the beam and tie rod assembly are connected with the tie rod of the balance arm from the top of the tower cap by the tensioning device, and then the assembly is hoisted by the tensioning device and connected with the tower top.

7. Install the boom, lift the boom to make it slightly inclined, and then connect it to the top of the tower with 2× 1 pin; Lift the tie rod with the tower top device and the main lifting device.

8. Install the balance weights, hoist all the balance weights to the tail of the balance arm one by one, fix them with a pin shaft, and lock the balance weights together with a locking system.

9. Wear the trolley wire rope and lifting wire rope according to the instructions.

10, turn on the power supply of the tower crane, check the assembly and passage of the tower section, and conduct preliminary debugging.

1 1, tower crane is segmented, and the tower crane will be jacked up according to the site specific conditions until it meets the requirements (plus 10 standard segmentation).

12, comprehensive debugging of tower crane.

Tower crane disassembly standard process I. Tower crane disassembly process

Disassembly sequence: the tower crane descends (descends to the height of the roof) → counterweight (the third position at the tail of the balance arm is left 1 counterweight) → counterweight → balance arm → tower top → cab → slewing mechanism → jacket and standard section.

Second, the specific disassembly process of tower crane

Because there is not enough space and space on the construction site, we can negotiate with the manufacturer to remove and install the removed parts as soon as possible in order to occupy as little space as possible. Specific hoisting procedures are as follows:

1. Before the tower crane descends, check whether the limit device and safety device of the tower crane are sensitive and reliable.

2. Preparations before the tower crane descends: it is necessary to check whether the hydraulic system works normally; Whether there are unsafe factors; The safety and quality of the wall-attached part must be checked.

3, matters needing attention in the process of reducing cross section

1) From the time when the joint is ready to be lowered, it is forbidden to rotate or operate the boom from the time when the standard joint and the lower bearing joint are removed to the time when the joint is lowered.

2) When lowering the joint, there must be a special person to command and take care of the power supply, operate the climbing mechanism and tighten the bolts. Non-related operators shall not board the climbing platform, and shall not start electrical equipment such as pump valve switch without authorization.

3) The node dropping operation must be carried out during the day. If it is necessary to work at night under special circumstances, there must be sufficient lighting.

4) Only when the wind speed at the top is lower than 13m/s, if the wind suddenly increases during the knot falling, the knot falling operation must be stopped, and the rotation and jacket are connected into a whole with a pin shaft.

5) In the process of lowering the joint, the slewing mechanism should be braked tightly, and turning is prohibited. If a fault is found, it must be stopped immediately for inspection.

6) When the tower falls, the wall-attached device shall not be removed before it falls to the specified height.

7) In the process of lowering the joint, grease should be applied to the removed bolts.

8) After lowering the joint, tighten the bolts of the standard joint and rotating the lower bearing.

4, tower crane tower operation

1) Adjust the clearance between the guide wheel of the climbing frame and the tower, preferably 3 ~ 5 mm ... Move the trolley so that the upper center of gravity of the tower crane falls on the hinge point on the jack-up oil cylinder, then remove the eight high-strength bolts connecting the bracket and the tower body, and check whether the climbing claw affects the descending operation of the tower crane.

2) Start the hydraulic system. After the piston rod is fully extended, hang the jacking beam on the next step of the tower, remove the connecting bolt between the tower and the tower, and lift the piston rod slightly to separate the upper and lower supports from the tower. Push the standard joint out to the top of the lead-in beam, retract all piston rods, and make the climbing claw stop on the steps of the tower. Extend all piston rods again and hang the jack beam on the upper steps of the tower again. Retract all piston rods, connect the upper and lower brackets with the tower, and insert high-strength bolts.

3) The above is the process of descending the tower. When the tower descends continuously, the above process is repeated.

4) After being removed to the basic height of initial installation, it shall be removed by truck crane, and it must be removed in the order of removal.

Note: During disassembly, there must be a special person for on-site safety monitoring, and personnel are strictly prohibited from entering the operation site. At the same time, warning lines and obvious signs must be set up.

Crane operators should pay attention to the following items: 1. Rope threading: determine the center of gravity of the crane and choose the position of hanging rope. When using the snap ring, it is forbidden to force the snap ring laterally. The rope should be put on with an iron hook, and the arm should not reach under the hanging object. When lifting the hanging objects with hard edges or easy to slide, it is necessary to add pads and use lassos.

2. Rope hanging: Ropes shall be hung in sequence, and shall not be squeezed, crossed, kinked or twisted during rope hanging. Generally, suspension can be used, and the balance of the suspension must be protected; For goods that are easy to roll, slip or be too long, the rope method should be adopted and the hanging rope should be locked with a snap ring.

3. Trial hoisting: the lifting rope should be hung firmly, and the crane should be lifted slowly. The lifting rope should be tightened for a while, and the lifting should not be too high; When lifting objects 20 ~ 50 cm above the ground, pay attention to the parking inspection: the stability of the crane, the reliability of the brakes and the firmness of the binding; During trial hoisting, the command bell man, hook man and driver must be coordinated. If it is found that the center of gravity of the hoisted object is deviated or attached to other objects, the lifting must be stopped immediately, and measures must be taken to confirm the safety before lifting.

4. Rope release: The rope can only be released after falling, stopping and supporting. For hangers that are easy to roll, slide and disperse, use safety hooks to remove ropes. The hook shall not stand on the hanger. If it is difficult to remove the rope manually, other machines and tools should be used to assist. It is forbidden to climb lifting objects and ropes.

5. Pull the rope: After the weight is in place, put a wooden Fang on it, and then slowly pull out the rope by hand. It is not allowed to pull the rope obliquely or forcibly, and it is not allowed to turn the derrick. Crane rope shall not be used for lifting fragile, rolling and falling objects.

Correct operation specification for tower crane operation 1 principle of "ten don't hoist" 1, unclear command signal or illegal command not to hoist.

2, overload or unknown weight not hanging.

3. If the crane exceeds the span or fails to kick as required, it shall not be hoisted.

4. The workpiece is not firmly bound or unstable after binding.

5, hanging above someone or hook directly hanging on the weight without hanging.

6. The wire rope is seriously worn or broken and the safety device is ineffective.

7, the workpiece buried in the ground or frozen not hanging.

8, the light is dark, the line of sight is not clear, or not hanging in bad weather such as strong winds, heavy rains and fog above level 6.

9, angular objects without protective measures, more than 6 meters long or wide objects without traction rope.

10, the cable-stayed workpiece is not hoisted.

2 "Eight Prohibitions" standard 1. It is forbidden for personnel to stand in the lifting area or get into the hoisted goods.

2, it is forbidden to stand on the corner or the edge of the gondola car.

3, it is forbidden to stand on lifting objects.

4. It is forbidden to correct the hanging objects more than half a meter high by hand.

5. It is forbidden to put hands and feet into the padding directly below the hoisted goods.

6, it is forbidden to fast replay when heavy objects fall.

7, it is forbidden to use a crane to pull vehicles and hit objects.

8, it is strictly prohibited in the soft subgrade site lifting.

Code for construction safety of building engineering >:>