The sliding formwork is used for pouring high-rise structures (chimneys, silos, shafts, hyperbolic cooling towers, etc.), shear walls or tube structures, etcTool template。It consists of template system, hydraulic system and operating platform system.1、 Formwork system: including formwork, enclosure and lifting frame.Steel formwork is often used for formwork, which bears the lateral pressure of concrete. Its height depends on the sliding speed and the specified concrete formwork strength, about 1.0~1.2m. It is a cone with a small upper opening and a large lower opening. The net spacing at 2/3 of the formwork height below the upper opening of the formwork is the thickness of the structural section.An enclosure is arranged on the upper and lower part of the formwork (when the high-rise building is poured with the "sliding one pouring one" process, an additional enclosure can be added for the lengthening of the external formwork). The enclosure is channel steel or angle steel, which bears the horizontal force and friction force from the formwork, the vertical force generated by the dead weight of the formwork and the enclosure, and is calculated as a two-way curved multi span continuous beam supported by the lifting frame.The lifting frame is used to fix the enclosure, connect the formwork system and the operating platform system as a whole, and transfer all loads during construction toHydraulic jack, divided into double cross beam type (open frame) and single cross beam type (shaped frame), which are I-shaped steel or box shaped composite sections, calculated according to the frame.[1]
The sliding formwork is applicable to high-rise tower buildings.The plane of the building can be set out on the basic plane, which can be round, square, cross shaped, arc, solid, hollow, honeycomb or irregular.The most important thing is that the area must be straight upward and quite high.
Although most of the sliding form walls are straight, they can also be tapered, stepped or even curved.Tapered chimneys were built with slip forms as high as 1200 feet (366 meters).The sliding formwork has a wide range of uses in construction, except for storage bins and silos, it is mainly used in high-rise commercial buildings.The "core pipe" in the building generally includes the stairwell and the pipeline of public facilities, and it is also the main framework of high-rise buildings.Solve the problem of lateral load in frame structure.In high-rise buildings, slip form can be used to build load-bearing wall jointsprecast concrete Beam, slab andcast-in-place concrete。Other uses include water tower, dam intake tower, rocket silo, memorial tower (usually with a hotel on the top of the tower), cooling tower and air navigation command tower.
Design
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The sliding formwork can be basically divided into three categories of components:Lining plate, cross brace and yoke (i.e. II frame) formwork must be able to bear vertical and lateral loads.
There is a reinforcement platform above the working platform of the sliding formwork, and there is a finishing scaffold below.The weight of all formworks and operating platforms is supported by jack rods.The vertical load is transferred from the lining plate and platform plate to the cross brace, and from the II frame to the jack and the jack rod.The jack rod is inserted into the concrete with proper strength that is poured and tamped earlier, and the concrete poured and tamped successively after that shall not only bear its own weight, but also prevent the jack from lateral buckling.The calculated load shall include the operating load on the platform, 40 pounds/foot, in addition to the weight of all sliding formstwo(200 kg/mtwo）And 50 lb/ft (75 kg/m) scaffold length. In addition, the weight of reinforcement, box formwork and other items stored on the platform must be considered.
Another important vertical load is the friction of the sliding form during the sliding process.This value is difficult to estimate because it varies according to different conditions of concrete and operation.In order to reduce this friction, the formwork is generally made to tilt inward about 1/16 of the height of each foot of formwork (about 1/200 of the inclination).It is advisable to apply oil or paste plastic on the lining plate to prevent the formwork from absorbing water, because sufficient surface moisture plays a beneficial role in lubrication.It is recommended that the design criterion of 150 kg/m length should be 100 pounds of friction force per sigh length of formwork.The frictional resistance is transferred from the lining plate to the cross brace as a uniform load.The friction force and the load of the scaffold on the platform are transferred from the formwork to the II shaped frame.If the distance between the II shaped frames is short, the cross brace, as the beam lining plate in the horizontal direction, plays a role of distribution between the upper and lower cross braces.If the lining plate can bearShear, like steel plate orPlywoodThe cross brace is combined with the lining plate to form a girder.When the span is large and the load is heavy, the formwork in the form of frame separation must be used to bear the load.
Section and side view of sliding formwork and working platform of sliding formwork
In addition to the vertical load, the formwork must also bear the lateral water pressure of the plastic state concrete. The lining plate must be designed according to the water pressure between the transverse braces, and act as a cantilever outside the transverse braces.The cross brace here must be used as a transverse beam to bear horizontal pressure.In any case, the hydrostatic pressure of the concrete will never exceed the height of the formwork.
Allowable hydrostatic pressure of double cross braces of various sizes
The lining plate of the sliding formwork can be selected from several materials. The most commonly used wood is 1-inch thick and 3-6-inch wide slats.Steel formwork is sometimes used in sliding formwork, which costs several times more than wood formwork, but it is still cost-effective when multiple turnover is expected.There are other lining plate materials that are easy to use, as long as they are smooth, solid, somewhat tough, quite impermeable, and do not produce serious quality changes when the temperature changes.
In addition to the steel mold, the cross brace is generally made of wood, made of two or three pieces, and the joints are staggered.Two pieces of cross bracing are made of 2:00 thick wood, and three pieces of cross bracing can be made of 2:00 thick wood or a combination of 2:00 and 1:00 thick wood.Most of the formworks are designed with two transverse braces and some are designed with three transverse braces.
The II frame is designed as an inverted U shape, and its legs are connected with the transverse braces. These two legs are tensioned when bearing vertical loads, and they are used as cantilever beams when bearing lateral loads.The cross bar of the II frame must be designed as a beam to bear the bending moment generated by vertical and lateral loads.The jack supports its center.The steel II frame must be adjustable within a large range for use in different types of projects.
Jack system
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The lifting and support of formwork is an important aspect in the operation of sliding formwork.This is achieved by jack and jack support rod.The jacks are all approximately cylindrical with a hole in the center through which the jack jacks pass.Generally, it has two sets of tong ring clutches. When the jack climbs, it is held and loosened alternately. The height of each climb is determined by the stroke of the jack, which is usually 1 hour (2.54 cm).The rising speed is the stroke multiplied by the number of climbs per hour.The speed of the existing jack can exceed 20 hours (50.8 cm) per hour.In fact, the speed of formwork sliding is not controlled by the jack, but determined by the setting time of concrete.If the jack is operated too fast, the plastic concrete will fall from under the formwork.If it is too slow, the concrete will stick to the formwork, or even crack the concrete as the formwork is lifted.The most suitable jack speed is largely affected by the performance of concrete and air temperature.In dry and hot weather, the taxiing speed needs to be higher, while in wet and cold weather, it needs to be slower.For slip form operation, the speed shall not be less than 2 hours per hour (about 5 cm) or more than 30 hours per hour (about 76 cm).The speed range of normal operation is 6~18 hours per hour (about 15~46 cm). If calculated by 24 hours per day, it is about 8~14 hours per hour (about 20~35 cm).
The jack rod is generally designed for axial compression and must be free from deflection under load.When there is no concrete (such as under the beam or window opening), use 4X6 (about 10X "J" 15cm) brace to support.The jack rod is fastened on the brace by means of "J" bolt. The "J" bolt hooks the jack rod at one end and passes through the brace at the other end. A wood block is placed between the jack and the brace and tightened with nuts.In some cases, the jack rod can be suspended from a structure above the slip form, so that the jack rod is tensioned, which can increase the accuracy of the structure in the vertical direction. This method is used in the underground rocket silo support structure is supported on the ground at the excavation hole.The common spacing of jack rods is 4~9 feet (1.20~2.70 meters). The spacing of jacks is affected by the maximum allowable span of the cross brace, the radian of the wall, the lifting capacity of the jack and the need to place the jack at each corner.Generally, several jacks shall be concentrated at places with special heavy loads, such as platform beams, concrete hoppers and bridgehead platforms.The correct arrangement of the jack system is very important for the success of the sliding form operation.
Platform support design
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The working platform is directly supported on the formwork and lifted with the formwork as between the formwork.If the span is too large, beam or scaffold will be used to replace the platform joist.Platform panels and joists are designed for dead load plus local live load of 75 lb/fttwo(366 kg/mtwo）Or centralized live load design of concrete trolley or other construction machinery, whichever is heavier.Beam and scaffold can be divided into 40 pounds/foottwo(196 kg/mtwo）Design of uniformly distributed live load.
Maximum span of various platform panels
Spacing of platform joists
This is based on non motorized concrete trolley or 75 lb/fttwoThe live load of is the most dangerous case.The platform in the planing of sliding formwork must be designed to keep the plane size unchanged in all elevations of structural lifting.In order to achieve these goals and resist the wind, the platform must have sufficient support system on the plane.
The support system can be made of wood, steel brace, iron plate, truss or a combination of several of them.[2]
