Project overview
Xx Hangzhou R&D and Production Center Project is located in the south bank of Qiantang River. The total construction area of the project is 247,278? It is divided into three parts: South District (the third section), North District (the first section) and River (the second section).
The multifunctional hall in the second area is a composite structure of steel reinforced concrete structure and steel structure, with a diameter of 54m and three floors. The structure mainly includes four core tubes (from-4.0m to 15.835m at the bottom of core column steel foundation), 9.850m floor beam and slab, 16.550m floor beam and slab,16.550m-33.400m double column system and roof steel structure.
The concrete strength grade of the core tube is C40, and commercial concrete is pumped. The maximum coarse aggregate particle size is 25mm. The concrete strength grade of the steel reinforced concrete structural beam connecting the core tube is C45, and the pumped commercial concrete is adopted. The maximum particle size of coarse aggregate is 20mm.
Steel bars φ 32 and φ 25 of core wallboard are connected by mechanical straight thread. It was contracted by Zhejiang Jianyi Construction Group Co., Ltd. to undertake the construction of concrete structures. The main volume of the concrete structure of the multi-function hall is 1000 m3.
Engineering characteristics
(1) The engineering structure is complex, the shape is strange and novel, and the core steel reinforced concrete tube is arc. Belonging to major special structural engineering. See attached figure 1 for the plan of core steel reinforced concrete cylinder.
(2) The floors of this project are relatively high, which are12.050m and 6.700m respectively.
(3) The core wall panel is mass concrete, and certain temperature difference control measures must be taken.
Construction process arrangement
(1) Construction sequence → Installation and welding of steel core column and steel corbel in the first layer of core tube → Reinforcement connection and binding of core tube → Arrangement and installation of cooling tube → Arrangement and installation of temperature measuring holes → Formwork of core tube → Concrete pouring → Temperature measuring and curing of concrete → Installation and welding of steel core column and steel corbel in the second layer of core tube →
(2) The steel bars in the core tube of the steel bar project are all made on site. Set up a steel processing shed, equipped with a full set of steel processing machinery, and arrange full-time personnel to manage the whole process of steel processing acceptance, sampling test, production and processing, welding sampling test, finished product listing, classified stacking, verification and delivery, so as to ensure the quality of steel processing.
The butt joint of the main reinforcement of the concealed column of the core tube adopts mechanical straight thread connection. After entering the site for welding, the rebar in the project must be sampled and tested by a qualified central laboratory, and can only be put into construction after passing the test.
When processing steel bars, according to the construction arrangement, the processing and binding should be closely coordinated, and the first binding should be processed. The processed steel bars should be stacked according to the number, and the first used steel bars should be stacked on them to reduce unnecessary secondary handling.
After the rebar enters the site, before making and processing, check the cleanliness of the rebar surface, and clean up the attached oil, dirt and floating rust before use.
Steel bar blanking should be based on the number, diameter, length, quantity and length of steel bars, and the long material should be broken first and then the short material should be broken, so as to minimize and shorten the short end of steel bars and save steel.
Steel binding must be organized in strict accordance with the requirements of construction drawings. The size, spacing and location of steel binding should be accurate. The lap and anchorage length of all steel bars must meet the requirements of design and construction specifications.
In particular, it involves the joint treatment of the intersection of the main reinforcement and the steel beam. After full communication with the designer, the treatment measures are determined. After the steel bar is bound, the concrete cover pad must be adjusted to ensure the accurate position of the steel bar. When pouring concrete, it is easy to cause the displacement of steel dowel in wallboard and column, so measures should be taken to prevent the displacement of steel dowel when inserting steel dowel into structure.
When binding vertical and horizontal steel bars of shear wall, the intersection of two rows of steel bars around should be fastened at every point, and the middle part should be fastened every plum blossom. Support hooks are arranged between the two layers of the double-layer steel mesh to fix the spacing between the steel bars. The hook at the end of the steel bar should face the concrete.
(3) Formwork engineering
The core tube is supported by nine splints, and DN48 steel pipe and DN 14 screw are clamped longitudinally by ingot iron. Through calculation, it is determined that the vertical and horizontal spacing of φ 14 screw is 400mm, which meets the stress requirements of concrete construction. During construction, the width, height difference and smoothness of formwork joints should be strictly controlled, and the contact surface between formwork and concrete should be coated with HF-3 high-efficiency release agent to ensure the appearance quality of concrete after molding.
Strictly control the formwork removal time, and only when the temperature difference between the inside and outside of concrete tends to be consistent can the side formwork be removed. Form removal follows the principle of first supporting and then dismantling, with non-bearing parts first and bearing parts later, from top to bottom. Operators should stand in a safe place to avoid safety accidents, such as templates, connectors and supports. This section of formwork can only be transported out and piled up after it is completely dismantled.
After the formwork is dismantled, it should be cleaned in time and coated with release agent.
(4) Mass concrete engineering
Concrete pouring and tamping of core tube structure shall be carried out according to mass concrete construction.
Concrete adopts commercial concrete and is pumped.
1. Selection of raw materials
Concrete adopts C40 commercial concrete -R5≥40Mpa early strength concrete, which is provided by Pengcheng Commercial Concrete Company in Binjiang District. After expert argumentation, P.042.5R conch from Ningguo, Anhui Province was selected, which has fast early strength and low hydration heat. In order to prevent concrete cracks, Jinlong SPS mineral powder and 15mm polypropylene fiber were mixed, and 5 ~ 20 mm crushed stone was produced in Fuyang. Before concrete pouring, the concrete manufacturer first makes several groups of trial gradations with different contents, and then determines the following gradations according to the construction environment and design and construction requirements. Cement: water: yellow sand: gravel: admixture (HR 1-2c): mineral powder: polypropylene fiber = 320:163: 738:1020: 8.6:110. In each construction, the commercial concrete company originally used the quality assurance materials of commercial concrete, and the field testers cooperated with the concrete manufacturers to adjust the mixture ratio in time, strictly control the mold-entering temperature and slump, and ensure the construction quality and continuity of concrete.
2. Delay the cooling rate of concrete
After mass concrete pouring, in order to reduce the temperature difference between inside and outside during the heating-up stage and prevent surface cracks, the concrete should be watered and cured in time after initial setting. The concrete surface is covered with a plastic film and two sacks to keep the concrete surface moist, and cooling water pipes are buried in the concrete (see Figure 2 and Figure 3), and water is introduced from the initial setting of the concrete to reduce the hydration heat of the concrete.
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