1. Foundation Preparation before Tower Crane Installation
There are two types of foundations fortower cranes: track foundation and concrete foundation. The construction of the track foundation should meet the following requirements: (1) Subgrade Bearing Capacity: For light – dutytower cranes (with a lifting capacity of less than 30kN), it should be 60 – 100kPa; for medium – duty ones (with a lifting capacity of 31 – 150kN), it should be 101 – 200kPa; and for heavy – duty ones (with a lifting capacity of more than 150kN), it should be above 200kPa. (2) A track – spacing tie rod should be installed every 6m. The allowable deviation of the track gauge is 1/1000 of the nominal value and should not exceed ±3mm. (3) In the longitudinal and transverse directions, the inclination of the top surface of the steel rail must not be greater than 1/1000. (4) The gap between the steel rail joints should not be greater than 4mm and should be staggered with the joints on the other side of the track. The staggering distance should not be less than 1.5m. The joint should be supported on the sleepers, and the height difference between the two rail tops should not be greater than 2mm. (5) A buffer stop must be installed 1m away from the end of the track, and its height should not be less than the radius of the running wheel. A limit – switch bumper must be installed 2m away from the end of the track. (6) The connecting bolts of the fishplate should be tightened, and the base plates should be firmly fixed.
The concrete foundation of atower craneshould meet the following requirements: (1) The concrete strength grade should not be lower than C35. (2) The allowable deviation of the surface flatness of the foundation is 1/1000. (3) The position, elevation, perpendicularity of the embedded parts and the construction technology should meet the requirements of the factory – provided instruction manual.
When the tower crane is installed on the bottom plate within the building foundation pit, the punching – shear strength of the bottom plate must be checked. Generalmente, the longitudinal and transverse reinforcement should be densified, and the thickness of the bottom plate should be increased.
When the tower crane is installed on the side – slope support structure of the foundation pit, the strength and stability of the support structure must be checked. If the safety requirements are not met, the support structure must be strengthened.
When the tower crane is installed on the ground beside the foundation pit, the installation site must maintain a certain safe distance from the foundation pit. The soil beside the pit should be checked for anti – sliding, anti – overturning and anti – overall sliding. If the safety requirements are not met, support measures or pile foundations should be adopted.
Slopes and drainage facilities should be constructed beside the tracks of the tower crane and around the concrete foundation.
After the construction of the tower – crane foundation is completed, it can be put into use only after passing the acceptance inspection.
2. Installation and Dismantling Methods of Tower Cranes
The installation method of a tower crane is determined according to the structural type, weight of the crane and the specific site conditions. Generalmente, there are three methods: the integral self – erection method, the rotary erection method, and the vertical – installation self – lifting method. The dismantling method of the same tower crane is the same as the installation method, only in the reverse order.
(1) Installation Steps of the Integral Self – erection Method
The integral self – erection method uses the crane’s own equipment to complete the installation operation and is suitable for light – and medium – duty lower – slewing tower cranes. Taking the QT1 – 2 type tower crane as an example, the installation steps are as follows (Figure 14 – 34): 1 – Towing rod; 2 – Crane running frame; 3 – Front running wheel; 4 – Front towing wheel; 5 – Rear towing wheel; 6 – Crane luffing pulley block Before installation, the equipment and the laid tracks should be thoroughly inspected. Installation can be carried out only after confirmation.
Set up a temporary power supply more than 5m away from the installation point. Remove the towing rod of the crane, check and tighten the bolts at all parts; check the brakes of the hoisting and luffing winches. After confirmation, set up the guide – wheel frame and pulley frame (Figure 14 – 34a).
Start the luffing winch to make the crane running frame tilt slowly, and make the front running wheels fall on the track gradually. Remove the front towing wheels and move them out of the track (Figure 14 – 34.b).
Slowly release the brake of the luffing winch to make the rear running wheels of the crane fall on the track slowly (Figure 14 – 34c). Then open the lock cover of the limit – torque limiter of the slewing mechanism reducer, adjust the spring to make the friction disc contact tightly, and use the rail clamp to firmly clamp the rail. Load 4m³ of sand into the counterweight box and lock the box door. Untie the connecting rod between the boom and the towing wheel, and conduct a comprehensive inspection and lubrication of all parts of the crane again.
Start the luffing winch to erect the tower body (Figure 14 – 34d). After the tower body is erected, connect the tower body and the slewing platform into one body with pins and jack them tightly with two jacks (Figure 14 – 34e).
Disassemble the connecting rod between the tower body and the boom, and continue to start the luffing winch to pull up the boom until it reaches the horizontal position (Figure 14 – 34f).
Loosen the rail clamp, remove the pull plate and release the jacks. Adjust the spring of the slewing – mechanism limit – torque limiter. Then conduct a comprehensive inspection and lubrication of all mechanisms again, and the installation work is completed.
(2) Rotary Erection Method
The rotary erection method is generally suitable for tower cranes that need to be disassembled and transferred and are not self – lifting. This method generally uses a light – duty truck crane for assistance, assembles on the construction site, and uses its own hoisting mechanism to rotate the tower body to make it stand upright. Taking the TQ60/80 type tower crane as an example, the steps are briefly described as follows:
Lay the track as required and embed the ground anchor for erecting the tower body.
Install the running trolley and the portal frame on the track and install the counterweight.
Assemble the tower body and place it at the starting position of erection. Connect the lower end of the tower body to the hinge ear of the portal frame (Figure 14 – 35b).
Assemble the boom and install it in place. Install the luffing tie rod at its head, and connect the other end to the ground anchor through a cable.
Thread the erection – tower – body pulley block between the tower body and the boom, and tie the guy wires at the top of the boom and the top of the tower body. The lower end of the guy wire at the top of the boom is connected to the 150kN ground anchor; the lower end of the guy wire at the top of the tower is wound around the 50kN ground – anchor ring for lowering the tower body.
Erect the tower body. Start the winch to pull up the boom until its elevation angle is 45° – 60°, and then tighten and fix the guy wires (Figure 14 – 35c). Then start the winch again, and the tower body is gradually pulled up. When the tower body leaves the sleeper stack by 50cm, apply the brake for inspection. If there is no abnormal situation, continue to start the winch to make the tower body stand up slowly. When the tower body is close to the vertical position, slightly tighten the guy wire tied to the top of the tower for insurance and cooperate with the winch to make the tower body be in place slowly.
Start the hoisting winch to connect the counter – jib with the tower cap and fix it with a pull rope, and install the counterweight.
Lift the boom, thread the luffing wire rope and install it in place.
(3) Vertical – installation Self – lifting Method
This method is suitable for self – lifting tower cranes. The main approach is to use another crane (auxiliary machine) to vertically install all the components of the tower crane to be installed, except for the middle section of the tower body, at the installation position, and then use its own self – lifting device to install the middle section of the tower body. The installation steps of the vertical – installation self – lifting method are shown in Figure 14 – 36. The installation method of the middle section (standard section) is described in Section 14 – 2 – 4 – 6, the tower – body lifting, attachment and internal climbing of the tower crane. (a) Install the trolley; (b) Install the climbing frame; (c) Lift and install the tower; (d) Install the counter – jib; (e) Install the boom
3. Precautions for Tower – crane Assembly and Disassembly Operations
(1) The assembly and disassembly of the crane must be carried out by a professional team with a disassembly and assembly qualification certificate issued by the construction administrative department, and technical and safety personnel should be on – site for supervision. (2) Before the assembly and disassembly of the crane, according to the relevant factory – provided regulations, the assembly and disassembly operation method, quality requirements and safety technical measures should be prepared. After being approved by the enterprise’s technical director, it becomes the assembly and disassembly operation technical plan and should be communicated to all operating personnel. (3) The metal structure, track and metal casings of all electrical equipment of the crane should have a reliable grounding device, and the grounding resistance should not be greater than 4Ω. (4) The assembly and disassembly operations of the crane should be carried out during the day. When encountering severe weather such as strong winds, thick fog and rain or snow, the operations should be stopped. (5) The commander should be familiar with the assembly and disassembly operation plan, abide by the assembly and disassembly process and operating procedures, and use clear command signals for command. All personnel participating in the assembly and disassembly operations should follow the command. If the command signal is unclear or incorrect, the operation should be stopped, and the work should resume after the communication is clear. (6) When the assembly and disassembly personnel enter the work site, they should wear safety protection equipment. When working at heights, they should fasten their safety belts, be familiar with and earnestly implement the assembly and disassembly process and operating procedures. When abnormal situations or difficult problems are found, they should promptly report to the technical director and not act on their own to prevent accidents caused by improper handling. (7) When disassembling and assembling the boom of an upper – slewing and trolley – luffing tower crane, it should be carried out according to the disassembly and assembly requirements of the factory – provided instruction manual, and the balance of the crane should be maintained. (8) For structures connected by high – strength bolts, the connection bolts manufactured by the original factory should be used. Self – made bolts should have a quality – qualified test certificate; de lo contrario, they shall not be used. When connecting the bolts, a torque wrench or a special wrench should be used, and they should be tightened according to the assembly technical requirements. (9) During the assembly and disassembly operation process, when encountering unexpected situations such as sudden weather changes, sudden power outages and mechanical failures and unable to continue the operation in a short time, the disassembled and assembled parts must be made to reach a stable state and be fixed firmly. After inspection and confirmation that there are no hidden dangers, the operation can be stopped. (10) When installing the crane, the buffer stops for the cart running and the limit – switch bumpers must be installed firmly and reliably, and the safety protection devices such as railings, platforms, handrails and protective rings at all parts should be installed completely. (11) When dismantling a crane that cannot be disassembled by normal methods due to damage or other reasons, it must be carried out according to the safety disassembly plan approved by the technical department. (12) During the installation process of the crane, technical inspections must be carried out in stages. After the complete machine is installed, a complete – machine technical inspection and adjustment should be carried out. The actions of all mechanisms should be correct, stable and free of abnormal noises, the braking should be reliable, and all safety devices should be sensitive and effective. In the case of no load, the allowable deviation of the perpendicularity between the tower body and the foundation plane is 4/1000. After passing the staged and complete – machine inspections, the inspection records should be filled in. Only after being reviewed and signed by the technical director can it be put into use.
4. Transfer of Tower Cranes
Before the transfer of a tower crane, it should be lowered or disassembled in the reverse order of installation using similar methods, and then be transported as a whole or in a disassembled state. (1) For lower – slewing tower cranes transported as a whole, light – duty ones mostly adopt the full – trailer transportation method, while medium – and heavy – duty ones mostly adopt the semi – trailer transportation method. The tractor for towing can be that of a truck or a flat – bed trailer. Since the overall towing length exceeds the limit, the following points must be noted during towing:
Before towing, the towing route must be surveyed to fully understand the road width, curve radius, overhead wires, road undulations, etc.. Appropriate safety measures should be taken according to the actual situation.
If the road width is less than 7m, the curve radius is less than 10m, the overhead wires are lower than 4.5m, the clearance height of bridge and culvert holes is less than 4.5m, or the bearing capacity of the bridge is lower than 15t, passage is not allowed.
Before towing, the towing train should be equipped with taillights and brakes, and appropriate counterweight should be installed on the tractor.
The towing speed should not exceed 25km/h. When passing through curves, it should be driven at a low speed, and there should be a dedicated person in charge of ground command to ensure the smooth passage of the towing train.
During the towing process, inspections must be carried out at any time. If abnormal phenomena are found, they should be eliminated in time. (2) Self – lifting tower cranes and upper – slewing tower cranes such as the TQ60/80 type must be transported in a disassembled state. To facilitate loading, unloading and transportation and shorten the assembly and installation time, when disassembling the tower crane, it is not necessary to completely disassemble it, but to decompose it into several components. Por ejemplo, the entire undercarriage can be retained as a whole. También, according to the size characteristics of the structural components, the boom sections can be inserted into the standard tower – body sections, thereby compressing the transportation space and reducing transportation costs. Since self – lifting tower cranes are tall and the weight and outline dimensions of the components are relatively large, they must be transported by flat – bed trailers and loaded and unloaded with the cooperation of truck cranes.
