Super high-rise buildings are generally located in the city center, and the construction site in the city center is generally narrow. For the steel structure construction of super high-rise buildings, the steel structure members must be well prepared for entry, acceptance and stacking before hoisting, otherwise the hoisting construction of the whole project will be seriously affected. Take the construction of a super high-rise steel structure as an example. Due to the large number of steel structure members and limited space, they need to be stacked. In this case, if we don't make a detailed plan for the sequence and stacking of components entering the site, then during the hoisting process, the components that want to be hoisted may be pressed down by other components, or the components that need to be installed immediately have not yet entered the site, and the components that are pulled to the site don't want to be installed now, which will lead to repeated overturning and reverse transportation of components, resulting in confusion in the placement of components on the construction site. The main building of this super high-rise building has more than 10,000 steel members. Before construction and installation, the project department made a detailed construction hoisting plan and numbered each component. For each numbered component, its shape, weight, installation position, entry sequence and adjacent component numbers are all described in the scheme. According to the hoisting scheme, strengthen the acceptance before hoisting, and it is absolutely not allowed to enter the site for stacking without an established scheme.
2 Selection, arrangement and installation of vertical transportation equipment for steel structure members
2. 1 Selection of vertical transportation equipment There are a large number of steel structure members in this project, as well as a large number of ultra-high, ultra-long, overweight and eccentric members. In order to ensure the smooth completion of the hoisting work of steel structure members in this project, the core work is to select vertical transportation equipment that meets the hoisting scheme of this project. When selecting vertical transportation equipment, we should comprehensively consider the building shape, site conditions, installation location, convenience, safety and reliability of installation and disassembly.
2.2 Layout of vertical transportation equipment According to the site conditions, building shape and structural layout of this project, vertical transportation tasks and schemes are considered, and two or more tower cranes with super-long, super-large, overweight and eccentric components are hoisted at the same time. After detailed calculation, two internal climbing tower cranes are arranged in the core tube, and jack-up tower cranes are arranged around the podium to meet the needs of the working floor plane of the whole project.
2.3 In order to improve the efficiency of vertical transportation, an auxiliary system with external power (hoist boom) was adopted in the construction, which solved the climbing problem of two tower cranes and played a decisive role in advancing the construction period. The installation and removal of large internal climbing tower crane has always been a subject with complex technology and difficult construction in China. In this project, a set of methods for dismantling large internal climbing tower cranes is studied. Practice has proved that this method is safe and feasible, which not only successfully solves the problem of tower crane demolition in this project, but also provides reference for similar projects in China to try to use internal climbing tower cranes.
3 hoisting of steel structure members
Component hoisting is the key process of steel structure construction, and the speed and efficiency of hoisting are the key to the success or failure of the whole project construction. In the construction of the main steel structure of this super-high-rise building, due to the tight construction period and large hoisting amount, the method of regional hoisting, classification and double-machine hoisting is adopted in the project, which not only ensures the construction period, but also solves the hoisting problem of large mast in overweight, eccentric and super-high state.
4 Positioning measurement of steel structure members
In order to ensure the accurate positioning of the steel structure members of the main building of the super high-rise building and the absolute accuracy of the verticality and axis elevation of the whole project, the project department has formulated a special survey scheme with ultra-high standards to ensure the construction quality of the steel structure of the project and provide a reliable basis for the construction acceptance. The installation of steel structure members in super high-rise buildings is different from ordinary buildings. The installation of steel structure components in super high-rise buildings not only directly affects the quality of the whole project, but also has obvious influence on the construction period due to the huge number of components. If the positioning measurement scheme is unscientific and unreasonable, although the positioning is accurate and the verticality and axis elevation control of the project meet the requirements of the measurement scheme and specification, the installation, review and correction time of each component will be prolonged, which will greatly affect the construction period of the whole project. In this project, the installation process, installation time and the internal relationship between components are comprehensively analyzed. By summing up and making full use of modern high-tech measuring equipment, the standardized measuring process similar to the standardized assembly line is classified and partitioned. Personnel, post, area, time, type of work and scope are responsible for the survey work within their own scope, and take up their posts after the drill. Minimize the construction time delayed due to improper measurement, and basically put an end to rework and secondary installation caused by measurement errors. Based on the process summary of survey work, the original "integral correction" method is changed to "process tracking correction" method, which can ensure the engineering quality and greatly save the construction time.
5 Welding of steel structure members
Super-high-rise steel structure has the characteristics of large volume, many components, complex structure, large engineering quantity and high quality requirements. As an important process of steel structure construction, the lofting and welding of raw materials of steel structure components, the level and training of welders and the selection of welding technology are the powerful guarantee for the project to be "safe, high-quality and efficient". The aspect ratio of this super high-rise building is 1∶9, which is rare in China. In order to ensure the structural safety, the project department conducted a serious and in-depth study on the design documents, classified the steel structure components in the design documents, and set up a steel structure component lofting, blanking and pre-assembly factory. The welding operation in the factory should be completed on the standardized welding production line of modern high-tech welding equipment as far as possible, and the convenience of horizontal and vertical transportation should be fully considered to minimize the welding operation on site. Yes, the welding workload on site is amazing, so the project set up a welding QC team to make use of all available tools and means to invent and learn from each other. Aiming at the welding task of this project, combining the high-altitude part and the suspended part of the component, the feasibility of safe operation and construction protection is ensured, and the mature semi-automatic welding process of CO2 gas protection is improved, which fundamentally solves the welding problems such as vertical welding, oblique vertical welding and fillet welding, and ensures the integrity of the steel structure.
6 how to solve the contradiction between construction period and quality
Compared with ordinary concrete buildings, super-high-rise steel structures have the characteristics of more components, tight construction period and high quality requirements. How to solve the contradiction between quality and construction period depends not only on scientific management, strict construction organization and factory pre-assembly of components, but also on boldly applying new technologies, new processes and new equipment suitable for this project according to the engineering characteristics as far as possible. The bonus of the main steel structure members of this super high-rise building is 15000 pieces, weighing about 25000t, and the project amount of profiled steel plates, welding studs and welds is tens of thousands, so the construction period is particularly tight. If it meets the quality standards of European specifications, it needs to be completed on time according to the construction period agreed in the contract, and the contradiction between construction period and quality is particularly prominent. In order to solve the contradiction between construction period and quality and ensure the "safety, high quality and high speed" of the project, a scientific management organization system must be established. To this end, the project has set up a project management department to carry out construction in strict accordance with the project management law, and implement the project manager responsibility system and full contract management.
7 safety management
Safety is progress, and safe construction will bring benefits. Without security, nothing can be said. The safety management of this project focuses on aerial work, including aerial falling, aerial welding spark protection and falling objects, which is very dangerous in construction. Therefore, we adhere to the 16-character policy of "strict requirements, standardized operation, prevention first, and prevention of delays" to pay attention to safety work and prevent safety accidents. First, the director of safety education should persevere and emphasize the importance of safety production every time, whether it is a general meeting or a small meeting; Hang slogans and warning signs in eye-catching places on the construction site to remind employees to pay attention to safety in production, and safety awareness runs through every working procedure and everyone.
The second is to strengthen the leadership of safety work. The project department shall set up a safety work leading group, clarify the safety work responsibilities of leading groups at all levels, sign a safety work responsibility letter, and ensure that everyone is responsible for safety work and people are caught everywhere. Third, strengthen safety training, formulate a complete safety production training system according to the safety characteristics of this project, select training contents, determine training targets, and carry out targeted training. The fourth is to do a good job in safety protection. In order to ensure the personal safety of employees and distribute all kinds of safety protection articles to employees in time, a strict safety protection system has been formulated. When entering the construction site, you must wear a safety helmet; Safety belts must be worn for aerial work. Fifth, do a good job in the inspection and implementation of safety work. The leaders of the project department and the construction team are on duty at the construction site in turn for 24 hours to eliminate all kinds of hidden dangers in time together with the safety officer. At the same time, carry out "three inspections" on a regular basis, that is, check whether the operation is standardized, whether the protective measures are in place, and whether the potential safety hazards have been eliminated, so as to ensure that no gaps or dead ends are left in the inspection.
8 conclusion
With the rapid development of super-high-rise building technology, the construction technology of super-high-rise buildings in China has also been significantly improved. How to improve and optimize the problems encountered in the construction process is still an important issue for our practitioners to think about at present.
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