Concrete slipform construction technology for the

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Shaft concrete slip form construction technology

for surge shaft and traffic shaft of hydropower station and pump house, it is generally a high cylindrical reason: thin-walled structure, one is surrounding rock lined with concrete, and the other is reinforced concrete exposed thin-walled cylinder. The slip form construction is the most advantageous for these structures, but if the design, manufacturing process and lifting mode of the slip form structure are not properly selected, it is difficult to reflect its advantages. The construction method of shaft slip form can also be used in other high towers, pier walls and frame structures. It is very necessary to study the optimal design scheme for different situations

2 structural design essentials

2.1 structural layout form

shaft slip form structure can be divided into pull-up type and top-up type according to different lifting methods, as shown in Figure 1 and Figure 2. It is more economical to use the pull-up type for the surrounding rock lining shaft. The pull-up type is to set a bearing frame at the wellhead, and the jack is inverted on the beam of the bearing frame. The discovery that the bearing beam can be arranged is a very special answer given by the important materials research institute in the face of the global concern about the supply and demand of rare earth materials. It can also be arranged in the radial direction or in the polygon. If the number of jacks is small, it can be arranged in the radial direction, and if the number is large, it should be arranged in the polygon. The jack is gyd-35 type, the working lifting capacity is 1.5T, and the pull rod of the jack is Φ 25 reinforcement, the lower end of which is directly welded to the shroud. The pull rod shall be made into a 3M long section, which shall be connected with M20 thread. One section shall be recovered after each section is pulled out. The sliding form structure of the exposed surge shaft must adopt the jacking type. The jacking type is that the chord is welded on the inner ring to place the jack, and the jack support rod adopts Φ 48 bent steel pipe. Qyd-60 type jack is adopted. The inner hole of this jack is 50mm and the working lifting capacity is 3T. One layer of horizontal and vertical connecting rod shall be installed every one meter when the jack climbs. The two ends of one layer of horizontal connecting steel pipe shall be able to top the concrete every three layers. If it is not long enough, a short steel bar can be connected to the concrete. The jacking slip form must be provided with an "open" shaped lifting frame. The purpose of the lifting frame is to ensure the relative position of the inner and outer formworks and transfer the lifting force of the jack to the outer formworks

2.2 formwork

2.2.1 strength and stiffness of formwork

the formwork is a rib structure welded by the enclosure and the panel. During concrete pouring, due to the symmetrical load, the internal force of the formwork is axial force, and it is eccentrically tensioned during lifting. During deviation adjustment, it is distributed load when it is squeezed on the concrete while it is away from the concrete and subjected to the concentrated force of the jack. The enclosure of the formwork generates a bending moment, and the whole is subject to a large eccentric tension. Therefore, the compressive and bending strength of the panel and the enclosure shall be calculated, and the stiffness of the formwork under large eccentric tension shall be calculated. The panel of the formwork is generally made of 2mm ~ 4mm steel plate, and the shroud is welded with 5mm ~ 8mm steel plate to form an annular beam with groove section. The groove mouth faces the panel, and the width of the groove wing is about 3% of the shaft diameter. As the panel is too thin to participate in the overall stiffness calculation, diagonal web members shall be welded between the upper and lower shroud to form an annular truss

2.2.2 formwork interface

the panel of the formwork must have more than two wedge-shaped interfaces. The width of the wedge-shaped formwork is 5cm ~ 10cm, and the radial slope is 1:0.5. When the slip form is stopped due to unexpected reasons, a small section of the enclosure can be cut off, and the wedge-shaped formwork will automatically fall out, and the formwork will lose its overall arch function, that is, 50t screw jack and hydraulic jack can be used to jack up the formwork and then recover to continue the construction

2.2.3 height of formwork

the determination of formwork height shall meet three principles: ① the pouring time of each layer of concrete shall not exceed the interval time specified in the specification; ② The sliding speed V (m/h) determined by the machine shift footage a (m/machine shift) to meet the progress requirements; ③ The mold strength is (0.05 ~ 0.1) MPa. According to the temperature and test data, the strength can be calculated as (0.05 ~ 0.1) mpa

* this sliding technology was applied to the ship lift tower column of Yantan Hydropower Station and won the second prize of Guangxi 1997 science and technology progress award. The age required is t (hours). Principle ① means that three layers of concrete can be poured in the formwork, so the height of the formwork should not be small. Unfortunately, due to the constraints of many factors, the traditional experimental methods are limited to 90cm., The height h of formwork determined by principles ② and ③ is:

for example, if the pouring height of machine shift is required to be a=2.4m, and t=4 hours determined by temperature, then h=1.2m. Generally, the height of formwork is 90cm ~ 150cm. If the pouring speed is specified and the temperature is low, the accelerator shall be used to meet the calculation; If it is too late for rebar binding and welding and the temperature is high, retarder shall be added to meet the calculation

2.2.4 formwork fabrication slope

the shaft is generally a cylinder. The internal and external formworks only generate axial force under the lateral pressure generated by concrete pouring and vibration, and the forces on the upper and lower enclosures are basically the same. The slope of the formworks changes little before and after concrete pouring. Therefore, the formwork shall be made into a standard slope of 1.5 ‰. For the internal formwork:

Φ 1 top =d+1.5 ‰ h

Φ 2=d-1.5 ‰ h

for external mold:

Φ 1 top =d-1.5 ‰ h

Φ 2=d+1.5 ‰ h

where: Φ 1. The top is the diameter of the top circle of the formwork; Φ 2. The intelligent technology of plastic injection molding is the diameter of the bottom circle of the template; D is the design inner diameter of the shaft; D is the design outer diameter of shaft concrete. If the shaft is a rectangular frame, the internal formwork shall be made into a standard slope, and the external formwork shall be made into a vertical one, because the stiffness of the lifting frame is limited. The four outer corners shall be tapered rounded. If the slope of the formwork is not enough, the concrete will crack. If the slope is too large, slurry leakage will occur and the concrete surface will be rough

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