Several problems of tower crane construction in high-rise buildings.

Jack-up tower crane is the first choice of lifting and transportation equipment for high-rise and super-high-rise building construction. This paper expounds several problems that need to be properly solved around the selection of tower crane.

1, about what kind of tower crane to choose

When choosing a tower crane, you should first choose a jack-up tower crane with appropriate parameters. Among these parameters, the most important are the main parameters: amplitude, maximum amplitude lifting weight and lifting height. However, when determining the main parameters, it is necessary to determine which type of tower crane to choose: internal climbing tower crane or attached tower crane; Is it a boom tower crane or a trolley boom horizontal boom tower crane?

Experience shows that the function of 1 40t m internal climbing tower crane can reach the function of 1 80t m attached tower crane. Attached tower crane should be equipped with more standard sections of tower body, and necessary number of attachment rods and corresponding anchorage devices. Therefore, from the perspective of saving one-time investment, it is economical and reasonable to choose the internal climbing tower crane. However, in order to ensure safe production and obtain the best benefit, the construction organization design of internal climbing tower crane hoisting construction and the tower crane disassembly scheme after the structure is completed should be done well.

At present, domestic jack-up cranes are mostly trolley luffing horizontal jib jack-up cranes, and only a few factories produce a small number of pitching luffing jib cranes. Therefore, from the supply point of view, it is more convenient to choose the horizontal arm tower crane. However, it is a reasonable choice to build a tower-shaped high-rise building in an environment like a forest. Because the suspender of the compression bar can freely pitch, the suspender will neither fluctuate on the adjacent high-rise buildings nor collide with the surrounding high-rise buildings. It is precisely because of the above characteristics of the boom jack-up tower crane that six boom jack-up tower cranes were used in the construction of the Hongkong and Shanghai Banking Corporation Building. For the same reason, some Southeast Asian countries have introduced some mobile jack-up tower cranes from China for high-rise building construction in recent years.

Buy a tower crane or rent a tower crane.

The cost of purchasing 1 set120t m tower crane is about 165438+ ten thousand yuan, which is not a small sum for a construction contractor. Besides interest, drivers, maintenance technicians and electricians must receive monthly wages and bonuses, as well as electricity, oil and spare parts. After the project is completed, the whole machine will be transported to the base for storage and maintenance, which requires another fee.

The advantages of leasing 1 tower crane are as follows: (1) There is no need to take care of the tower crane, and the leasing company is responsible for the driving, maintenance and repair of the tower crane; (2) There is no need to ask about the access, warehousing and maintenance of tower cranes. In other words, as long as you pay the monthly rent, you can get the desired lifting service, and nothing else needs to be done.

As for the calculation of monthly rent of tower crane, there is no unified regulation to follow so far. The following are two different calculation methods of monthly rent of tower crane.

One is the investment profit method.

120 t m-class tower crane, with a height of 80m at the hinge point of the arm root and a length of 50m at the price of 165438+ 10,000 yuan, with a service life of 8 years and an annual work of 10 month.

(1) The one-time investment of tower crane is 165438+ ten thousand yuan;

(2) The annual interest rate is 12%, and the total interest for 8 years is10.56 million yuan;

(3) The annual depreciation rate is 10%, and the total depreciation for 8 years is 880,000 yuan;

(4) The annual maintenance cost is 10%, and the total expenditure for 8 years is 880,000 yuan;

(5) The annual rate of insurance and management fees is 5%, totaling 440,000 yuan;

(6) After 8 years, the residual value is 200,000 yuan;

The second is the Baugerate method.

120 t m-class tower crane, with a height of 80m at the hinge point of the arm root and a length of 50m at the price of 165438+ 10,000 yuan, a service life of 10 years, and an annual working time of 9 months.

(1) The one-time investment of tower crane is 165438+ ten thousand yuan;

(2) The monthly interest and depreciation rate is 1.5%, compared with 1.98 million yuan in 2000;

(3) The monthly miscellaneous expenses for maintenance, repair, operation and management are 1. 1%, totaling10.089 million yuan;

(4) After10 years, the residual value is 1.5 million yuan;

Affected by the market economy, the monthly rent of tower cranes fluctuates greatly. In the first two years, the demand exceeds the supply, and the monthly rent depends on the seller's market. The rent has been high, reaching 70,000 yuan/month at the highest. At present, the monthly rent of tower crane has dropped greatly, which is close to the calculation result here. If the monthly rent is 55,000 yuan, the total investment (the cost of purchasing tower cranes) can be recovered after two years. Therefore, it seems more economical to buy 1 tower crane as a fixed asset if there are follow-up projects waiting for tower crane construction, or if there are certain conditions in base and logistics management.

Through comparative analysis, if it is determined to buy 1 tower crane, it is necessary to study which tower crane is the most economical to buy 1.

The cost analysis of tower crane shows that the cost of 50m boom tower crane is about 10% higher than that of 40m boom tower crane. However, the effective working range of 50m boom tower crane is about 35% larger than that of 40m boom tower crane. Using a longer boom can bring more convenience and flexibility to the construction, and expand the service scope of tower crane.

The cost analysis of tower crane also shows that under the same lifting capacity (or the same type of tower crane), the cost of rail tower crane is much higher than that of fixed tower crane, so we should buy fixed tower crane from the perspective of saving the cost of purchasing tower crane. However, it must be noted that there are two types of fixed tower cranes: one is fixed underframe, and the other is fixed tower foundation. The tower crane with fixed tower foundation section is the cheapest, which is cheaper than the rail tower crane 10% ~ 12.5%.

3, the practice of tower crane foundation

The common practice of the foundation of the track tower crane is to tamp the foundation or make a 1 layer 3: 7 lime-soil cushion, then lay the gravel ballast, then put the wooden sleeper and lay the track on the wooden sleeper. This method consumes a lot of wood and has a short service life, which is extremely unsuitable for heavy tower cranes. At present, it is suggested to erect reinforced concrete floor slab or reinforced concrete sleeper beam on the basis of compaction, fix I-beam on the floor slab or sleeper beam with embedded parts, and then install track on I-beam. In order to improve the efficiency and save the cost of track laying, reinforced concrete sleeper beams, I-steel brackets and rails are often assembled together to form an assembled reinforced concrete track foundation with a length of12.5m.. This kind of track foundation is very suitable for heavy jack-up cranes such as FO/23B, HK40/2 1B and H3/36B.

Block reinforced concrete foundation is most suitable for jack-up tower crane with fixed underframe. On the basis of high ground durability, the size of the concrete foundation slab should be 200cm×200cm×50cm, and the top and bottom of the slab should be reinforced in both directions. If the tower crane must be installed near the deep foundation pit, bored pile cap foundation should be adopted to ensure the firmness and stability of the tower crane foundation, and measures should be taken to prevent the slope of the foundation pit from collapsing.

The foundation of jack-up tower crane with fixed tower body must meet two requirements: first, the load on the upper part of tower crane must be evenly transferred to the foundation, and it must not exceed the ground bearing capacity; The second is to keep the tower crane stable without tipping over under various unfavorable working conditions. So the foundation of this tower crane is quite huge, and the weight of the foundation is equivalent to the weight of the tower crane. The foundation weight of this fixed tower crane is closely related to the free height of the tower crane. The higher the free height, the greater the foundation weight. Take FO/23B tower crane as an example. When its free height is 59.8m, the size of concrete foundation should reach 6.5m× 6.5m×1.7m. If the tower crane needs to be erected near the deep foundation pit in the foundation construction stage and the topsoil condition is poor, the foundation must also be supported by bored piles. Therefore, in order to save the cost of foundation construction, it is suggested that the whole mass concrete foundation should be decomposed into several precast concrete strips to form an assembled reinforced concrete foundation for repeated use, and the cost of tower crane foundation decomposed into each project should be minimized.

4, about ensuring safety in production

Summarize the experience of building construction with tower crane at home and abroad. In order to ensure safe production, we must do the following.

(1) Conduct 1 annual inspection every year and 1 comprehensive in-depth inspection every four years. The annual inspection and the inspection after each transfer and installation shall be carried out by the relevant lifting and transportation equipment safety inspection department of the local labor bureau. 4 years, 1 time comprehensive in-depth inspection, in addition to the Labor Bureau to send personnel to participate, you can also invite experienced engineering and technical personnel in tower crane design, installation and use to participate. The annual inspection and four-year 1 inspection should make an authoritative evaluation of the technical status of tower cranes, and point out the possible hidden dangers in detail, so as to carry out timely and thoughtful maintenance and nip the accident in the bud.

Tower crane drivers must be qualified personnel with professional training and certain driving experience, aged 18. Each tower crane is equipped with a working log of 1 this tower crane, and the tower crane driver on duty should carefully fill in the general situation of tower crane work, environmental conditions, operation characteristics of tower crane mechanism and maintenance carried out on that day.

Before leaving the machine at the end of the work shift, the driver of the track tower crane must clamp the track clamp to prevent the tower crane from overturning when the night wind blows out of the track.

In China, when several tower cranes are built around a project, the minimum safe operating distance between similar parts of two adjacent tower cranes is generally 5m. Recently, it is stipulated in foreign countries that the minimum distance between two adjacent tower cranes is 2m, and the minimum clear distance between the bottom of the component hoisted by the tower crane and the highest point (tower top) of the adjacent tower crane is 2m. Relevant people believe that as long as they concentrate and operate carefully, they can deal with it according to this new foreign regulation.

According to the usual regulations in our country, tower cranes are not allowed to lift operators. However, foreign countries have made new regulations based on the reality: under certain conditions, tower cranes can also improve operators. The specific conditions are as follows.

(1) There must be a spring buffer device at the bottom of the manned hanging basket, and there should be a high and closed grid enclosure structure, safe and reliable slings and safety protection covers around the hanging basket.

(2) Lifting personnel hanging basket shall be inspected by full-time personnel of safety inspection department 2 weeks in advance before the first use.

(3) The tower crane shall be inspected by the full-time personnel of the safety inspection department before the first lifting.

Recently, foreign data also introduced that when the concrete hopper with a special operation platform is used to lift concrete, the tower crane can also transport 1 concrete workers to the pouring place for concrete pouring and vibrating, thus avoiding the need to set up a special operation platform for concrete pouring along the large formwork, which not only simplifies the construction, but also saves the cost. This experience deserves attention and emulation.

For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd