today, Huai'an Crane Leasing Company Let's introduce some common lifting methods and have a look!

According to the different structural types and construction conditions, the steel grid can be installed by the high-altitude assembly method, the overall installation method or the high-altitude sliding method.

1、 The overhead assembly method is used for the installation of the steel space truss. The overhead assembly method is to first set up the assembly support at the design location, and then use a crane to lift the space truss components (or blocks) to the design location in the air, and then assemble them on the support. This method sometimes does not need large lifting equipment, but the amount of assembled support is large, and there are many high-altitude operations. Therefore, it is suitable for steel space grids connected by high-strength bolts and made of section steel or steel pipe space grids with bolt ball joints. At present, some steel space grids are still constructed by this method.

2、 Integral installation method The integral installation method is to first assemble the space truss on the ground into a whole, and then lift it to the design position with lifting equipment to fix it. This construction method does not need tall assembly supports, and there are few high-altitude operations, which can easily ensure the welding quality. However, the lifting equipment with large lifting capacity is required, and the technology is complex. Therefore, this method is more suitable for steel space grids with spherical joints (especially three-dimensional space grids with more members). According to the different equipment used, the overall installation method can be divided into multi machine lifting method, pole pulling lifting method, jack lifting method and jack lifting method.

1. Multi crane lifting method This method is used for small and medium-sized space truss structures with small height and weight. Before installation, the grid structure shall be assembled in a staggered position on the ground (that is, the assembly position shall be staggered a certain distance from the installation axis to avoid the position of the column). Then, multiple cranes (mostly crawler cranes or truck cranes) are used to lift the assembled grid structure to the top of the column as a whole, and then it is moved in the air and then dropped in place for fixation.

(1) In order to prevent the grid from colliding with the column during the overall lifting of the grid, the staggered distance depends on the clear distance between the grid and the column or the column bracket during the lifting of the grid, which should generally not be less than 10~l125px. At the same time, the convenience of the grid assembly and the convenience of the crane when moving in the air should be considered. If necessary, it can negotiate with the design unit to leave some edge members of the grid for welding after the grid is lifted, or change some column brackets that affect the lifting of the grid. After the steel grid is processed in the metal structure factory, the plane truss or three-dimensional truss that is assembled into small units by single pieces will be transported to the construction site. The construction site assembly means that the small unit truss will be assembled into the whole grid at the assembly position. The key to the assembly of space truss is to control the size of the axis support of the space truss frame (the welding shrinkage shall be pre placed) and the requirements for arch camber. The welding of space truss is mainly the welding of sphere and steel pipe. Generally, equal strength butt welding is adopted. For safety reasons, 6~8mm fillet weld is added at the butt welding position. For weldments with pipe wall thickness greater than 4mm, the interface should be made into groove. In order to make the butt weld even and the length of steel pipe slightly adjustable, casing can be added. During assembly, the upper and lower chords shall be installed first, and then the diagonal web members shall be installed. After all the steel pipes between the two trusses are put in and corrected, the steel pipes shall be welded one by one.

(2) The medium and small space grids are usually lifted by four crawler cranes (or truck cranes or tire cranes), or two crawler cranes or one pole. If the weight of the grid is small or the lifting capacity of four cranes meets the requirements, four cranes should be arranged on both sides of the grid, so that as long as four cranes rotate at the same time, the requirements for the overhead displacement of the grid will be completed. The key to multi crane lifting is to keep the lifting speed of each crane consistent, otherwise some cranes will be overloaded, the grid will be twisted, and the welds will crack. For this reason, the lifting speed of each crane shall be measured before lifting, so that it can be mastered during lifting. When the grid is lifted to about 750px higher than the elevation of the column top, move the grid in the air and move it above the column top. When the space truss is placed, in order to make the center line of the space truss accurately coincide with the center line of the column top, a steel wire rope is tied at each corner of the space truss in advance, and the chain block is used for alignment and positioning.

2. At present, the pole pulling lifting method is widely used in the installation of large steel pipe grid structures with spherical joints. When this method is used for construction, the space truss shall be assembled in a staggered manner on the ground first, and then the space truss shall be lifted to the top of the column as a whole by using multiple single leg pull rods. The space truss shall be displaced in the air and installed in the position.  

(1) Principle of aerial displacement aerial displacement is the key to this method. Aerial displacement is to make the grid move horizontally by using the unequal horizontal force in the lifting pulley blocks on both sides of each pole. When the grid is shifted in the air, at least two or more pull rods are required to lift the grid, and the lifting pulley block on the same side does not move. Therefore, when the grid is shifted in the air, it is only translated without tilting. Since the pulley block on the same side is not moving, the grid can control the circumferential movement in addition to translation, which will cause a slight decline of the grid. The direction of the space truss shifting in the air is related to the arrangement of the pulling rods.

(2) Selection and arrangement of lifting equipment selection and arrangement of lifting equipment is an important issue in the construction of grid truss pole lifting. The contents include: selection of pole pulling and layout of lifting points, layout of cable wind rope and ground anchor, threading of lifting pulley block and lifting point rigging, layout of winch, etc. The selection of pulling rod depends on the load it bears and the arrangement of lifting points. The calculated load when installing the grid is: Q=(K1 Q1+Q2+Q3) · K (kN), where Q1 - dead weight of the grid (kN); K1 - load factor 1.1 (if the weight of the grid structure is calculated accurately, it can be taken as 1.0); Q2 - dead weight of additional equipment (including purlins, ventilation pipes, scaffolds, etc.) (kN); Q3 -- dead weight of lifting appliance (kN); K - non-uniform coefficient of force caused by lifting difference. If the weight of space truss is basically uniform and the lifting difference at each point is controlled below 250px, the coefficient is 1.30.

The layout of the lifting points of the grid is not only related to the lifting scheme, but also related to the mechanical performance of the grid during lifting. In the lifting process of space truss, not only the internal force of some members may exceed the calculated internal force at the design time, but also the internal force symbol of some members may change and make the members unstable. Therefore, the number and position of lifting points shall be determined by checking calculation of grid frame lifting. However, on the premise that the lifting capacity, lifting stress and grid stiffness are met, the number of pulling rods and lifting points shall be minimized. The cable wind rope shall be arranged so that multiple pullers are connected to each other as a whole to increase the overall stability. Each pole shall have at least 6 wind ropes, which shall be calculated and selected according to the wind load, lifting weight, pole deflection, initial stress of wind rope and other loads, and the most unfavorable combination. The ground anchor shall also be calculated and determined. The force of lifting pulley block can be calculated according to the actual force, and the pulley specification can be selected according to the calculation results. The specification of the winch shall be determined according to the internal force of the lifting wire rope. In order to reduce the difference of catching and lifting, the winch of the same specification shall be used as far as possible.

(3) The axis controls the position of the assembled column of the grid structure, which shall be accurately measured according to the axis of the installed column, so as to eliminate the accumulation of axis errors when the column is installed. (4) After the grid frame is hoisted and removed by pulling rods, the pulling rods are enclosed in the grid frame, and should be removed by reverse removal method. This method is to hang two pairs of lifting pulley blocks at the top chord node of the grid to lift the rod, and then remove the rod section by section from the bottom section.

3. Electric screw lifting method The electric screw lifting method is similar to the plate lifting method. It uses the electric screw elevator used in the construction of the plate lifting project to lift the assembled steel grid on the ground to the design elevation as a whole. The advantage of this method is that no large hoisting equipment is needed and the construction is simple. The steel grid frame can only be lifted vertically rather than moved horizontally with an electric screw elevator. For this reason, the joist shall be set between two columns in the design, and the supporting point of the space truss shall fall on the joist. Since the grid does not move horizontally when it is lifted, it can be assembled in situ without dislocation.

3、 In recent years, the high-altitude parallel sliding method has been gradually used in the construction of space truss roof, which is especially suitable for the cinema, auditorium and other projects. In this construction method, the space truss is usually assembled by setting up an assembly platform on the roof of the building lobby (it can also be assembled by setting up an assembly platform on the stand of the auditorium). When the first assembly unit (or the first section) is assembled, it will fall onto the sliding track and slide forward for a certain distance with traction equipment. Next, assemble the second unit (or the second section) on the assembly platform, and slide forward together with the first assembly unit (or the first section) after assembly. In this way, the assembly will continue to slide forward section by section until the entire grid frame is assembled and slid to the position. After the sliding of the assembled grid, rollers can be set under the grid support to make the rollers slide on the sliding track; The support bottom plate can also be set under the grid support to make the support bottom plate slide along the embedded steel plate embedded on the reinforced concrete frame beam. The sliding of the grid can be pulled by a winch or a lever hoist. One or more points of traction can be adopted according to the traction force and the bearing capacity of the members between the supports of the grid.

When the grid frame slips, the asynchronous value at both ends shall not be greater than 50mm. When the sliding method is used to construct the grid, the following checking calculations shall be carried out for the grid during the sliding and assembly process:

1) When there is no fulcrum in the middle of the span, the internal force of the member and the deflection in the middle of the span;

2) When there is a support in the middle of the span, the internal force, fulcrum reaction and deflection value of the member. When the internal force of the member changes due to the addition of intermediate slide rail in the sliding element of the grid, temporary reinforcement measures should be taken to prevent instability. The overhead sliding method is used to construct the grid structure. Because the grid structure is assembled on the roof platform of the lobby, the danger of overhead operation is reduced; Compared with the high-altitude assembly method, the assembly platform is small, which can save materials and ensure the assembly quality of the grid; As sliding construction is used for space truss assembly, it can run parallel and cross with civil construction, thus shortening the construction period of the whole project; The construction equipment of high-altitude sliding method is simple and generally does not need large hoisting and installation equipment, so the construction cost can also be reduced.