1 analysis of construction characteristics and main technical problems of modern high-rise buildings
There are similarities and differences between the construction techniques of high-rise buildings and multi-storey buildings. It is also the basic process of construction according to the method of layer-by-layer construction; The difference is that high-rise buildings have the characteristics of deep foundation, many high-altitude operations, heavy workload, high technical difficulty in construction and long construction period. The main reason is that high-rise buildings are high in height and large in volume, which brings construction differences.
1. 1 The foundation is buried deeply.
In order to ensure the overall stability of high-rise buildings, the buried depth of the foundation should not be less than112 of the building height; When using pile foundation, it should not be less than115 of the building height (the length of pile is not included in the buried depth), and there should be at least one basement. Therefore, the general burial depth is at least 5m below the ground, and the foundation burial depth of super high-rise buildings even exceeds 20m. Deep foundation construction and foundation treatment are complicated. Especially in soft soil foundation, there are many choices of foundation construction schemes, which have great influence on cost and construction period. Studying and solving various deep foundation pit excavation and supporting technologies is one of the key points in high-rise building construction.
1.2 More aerial work
High-rise buildings have high height and heavy vertical transportation workload. Aerial work must deal with the vertical transportation of a large number of materials, products, machines, equipment and personnel. In the whole process of construction, we should conscientiously do a good job in high-altitude safety protection, fire prevention, water, electricity, communication, temporary toilets and other issues to prevent falling and collision accidents.
1.3 High-rise buildings are large in volume and quantity.
High-rise buildings have large quantities of works, many projects, many units and many types of work. Especially for some large and complex high-rise buildings, design, preparation and construction are often carried out at the same time. General contracting and subcontracting involve many units, and the cooperative relationship involves many departments. This brings great difficulties to the planning, organization, management and coordination of high-rise buildings. We must carefully build and strengthen centralized management. Of course, because there are many floors and working faces in high-rise buildings, we can make full use of time and space to carry out parallel flow three-dimensional intersection operation.
1.4 The construction conditions of high-rise buildings are complicated.
High-rise buildings are generally built in urban areas, with dense buildings and tight construction land. Try to compress the temporary works on site, reduce the storage of materials, products and equipment on site, reasonably select mechanical equipment according to the site conditions, and make full use of industrialized and commercialized finished products. During construction, adjacent buildings, roads and underground pipelines must also be protected from damage. In general, appropriate soil retaining or reinforcement measures should be taken in the process of foundation engineering construction. Especially in the process of foundation pit dewatering and excavation of adjacent buildings, we should pay close attention to whether there are cracks on the ground, roads and buildings on the ground and their development trend, and take corresponding technical measures in time to avoid damage to municipal engineering and adjacent buildings.
1.5 The construction period of high-rise buildings is long.
Generally, the average construction period of each multi-storey residence is about 10 month, while the average construction period of high-rise buildings is about 2 years.
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Shorten the construction period, mainly to shorten the construction period of structure and decoration. Various high-rise structural systems can adopt different construction methods. Cast-in-place concrete is the leading process of high-rise building construction, and reasonable selection of formwork system is one of the main ways to shorten the construction period and reduce the cost of the main structure.
1.6 requires high construction technology.
The construction technology of high-rise buildings is mainly reinforced concrete and steel as the main structural materials and related construction technologies, while reinforced concrete is mainly cast in place. We should focus on various construction technologies such as industrial formwork, steel bar connection, high-performance concrete, building products and structural installation. Secondly, decoration, fire protection, waterproofing, equipment and other requirements are higher. Diversification of plane types, personalization of facade modeling, and coordination of facade color with surrounding environment have become the general trend; The requirements of fire-fighting facilities are high, and the waterproofing of deep foundation, basement, wall, roof, kitchen and bathroom, and even the treatment of condensed water in pipes are higher than that of multi-storey buildings; High-rise buildings are equipped with many advanced decorations. All these put forward higher quality and technical requirements for construction.
2 High-rise building construction technology
2. 1 steel structure construction technology of high-rise building
In the steel structure construction of high-rise buildings, the installation construction is often carried out according to the characteristics of the building itself. In the construction process of high-rise buildings, there are very strict requirements for welding, hoisting, measurement and control, installation and demolition of steel structures. For high-rise buildings, the outer frame is all-steel structure, and the stability of the building structure is realized through the connection of steel beams, diagonal braces and core tubes, and the whole building structure is strengthened by laying floor steel plates and pouring concrete. The core walls of high-rise buildings generally have steel columns, the number of which should be more than 24, and the height and width should reach a certain proportion to ensure the stability of the overall structure. The hoisting process of steel structure should also be carried out according to certain methods, which determines the construction speed and quality of the whole project. Multi-machine hoisting and regional hoisting can effectively improve work efficiency. Welding technology of steel structure is also very important. The welding technology of high-rise building steel structure is relatively complex, with heavy construction tasks and high quality requirements. Reasonable welding technology must be adopted in the construction process to ensure the engineering quality. Carbon dioxide gas shielded welding, vertical welding and oblique vertical welding are generally used in engineering. When welding, attention should be paid to the extension length of welding wire, the cleaning of welding seam layer and the welding angle of welding gun, so as to form a complete welding operation method to complete the welding of engineering steel structure.
2.2 High-rise building concrete construction technology
In the process of high-rise building construction, concrete construction technology is particularly important, because the construction period of high-rise building is long, and the quality of concrete will be affected by climate and working conditions, so it is necessary to control the strength of concrete in the construction process. Before the project starts, concrete with different strength grades should be prepared according to the design requirements of high-rise buildings, and strength tests should be carried out. After the test results come out, the mixture ratio of concrete should be adjusted to meet the construction standards of high-rise buildings. The test mainly adjusts the mixture ratio of sand, cement and water. In the process of adjustment, adjustment should be made according to the actual situation, and the calculation of mixture ratio should be strictly controlled to ensure the construction quality of the project. In the process of pumping concrete, it should be carefully checked under the condition of strictly controlling the mixture ratio, raw materials and mixing. Because the construction unit didn't pay attention to the maintenance time in order to seize the construction period in high-rise building construction, and didn't determine the complete maintenance measures and specific plans when pouring large-area concrete, it is easy to cause quality problems of concrete structures. When curing concrete, measures should be taken from the aspects of personnel, water source, day and night curing time and coverage requirements. At the same time, we should pay attention to determine the maintenance time according to different cement varieties and strengthen the supervision of the maintenance period. In addition, attention should also be paid to cracks caused by concrete quality problems. Permanent expansion joints should be set during construction, and separation joints should be left at appropriate positions on the external wall. In order to avoid stress concentration caused by sudden change of structural section, attention should be paid to the configuration of structural reinforcement. For lightweight walls such as small concrete hollow blocks, constructional columns with spacing not more than three meters should be added, concrete waist beams should be added in the middle of each wall height, and constructional columns should be added at the unconstrained end of masonry. The reserved windows and doors should be reinforced with reinforced concrete frame and steel wire mesh. Special attention should be paid to the masonry requirements of beam bottom and the reasonable setting of roof insulation and gas barrier.
2.3 Foundation and measurement technology of high-rise buildings
Due to China's vast territory and complex geological environment, the foundation of high-rise buildings should be adapted to local conditions and adopted in various ways. If the foundation soil is complex, the bearing stratum is deep, and the buried depth of the basement is not large, pile foundation should be adopted. Precast piles have a long history of development and their quality is guaranteed. The method of determining the bearing capacity is clear. The prestressed hollow pipe pile has a large bearing capacity, and the precast pile is more suitable for areas with high groundwater level. However, this kind of pile has some problems, such as large amount of steel, high cost, loud construction noise and difficult pile cutting. Therefore, the foundation construction should adopt cast-in-place piles. Cast-in-place pile has strong adaptability, low noise and low cost, and can be taken as the development focus to realize mechanization. When the buried depth of foundation is large, the construction technology is difficult and it is not easy to ensure the construction safety, so open caisson or caisson method should be adopted for construction.
When surveying high-rise buildings, because there are many stories in high-rise buildings, high precision of construction survey is required. Therefore, before the project starts, we should make a survey plan, determine the measuring instruments, establish the construction control network according to the construction plan, project the control axis of the high-rise building onto the building surface in time, and then release the column line and other details according to the control axis for steel binding, formwork erection and concrete pouring. The construction survey of high-rise buildings generally adopts the combination of external control method and internal control method. When the external control method is used to measure the axis, the internal control method should be used every few layers to improve the accuracy and reduce the accumulation of vertical deviation. When the internal control method is adopted, the laser plumb instrument method is generally adopted. The first floor must be well controlled in plane, and four suitable positions should be selected as control points or the central "cross" should be adopted. When pouring the rising floor, it must be done. The construction survey of high-rise buildings should be carried out by practical methods according to the actual situation, but it must be proofread and rechecked to ensure accuracy.