In order to prevent the overall lifting of the network frame bumping with the column, the staggered distance depends on the net distance between the network frame the column the pillar's legs in the lifting process, generally less than 10 ~ 125px. At the same time, the convenience of the network frame assembly should be considered the convenience of the crane during the air displacement. When necessary, it can negotiate with the design unit to leave part of the edge rod of the network frame until the network frame is lifted, change part of the pillar leg that affects the lifting of the network frame.
After the steel truss is processed in the metal structure factory, the plane truss three-dimensional truss that is formed into small units is transported to the construction site. The key to the grid assembly is to control the size of the axis support of the grid frame (to be pre-shrinkable) the requirement of arching.
The net frame is mainly sphere steel pipe. Generally, equal strength butt welding is used. For the sake of the butt welding, add 6 ~ 8mm fillet weld. Welding parts with wall thickness greater than 4mm should be made into groove. In order to make the butt weld uniform the length of steel pipe slightly adjustable, casing can be added. During assembly, the upper lower chord rods are installed first, then the slanted belly rod is installed. After all the two steel pipes between trusses are put in corrected, then one by one steel pipe is installed.
In the installation of large steel tube network frame with ball joints, the method of bar pulling lifting is commonly used in China at present. In this method of construction, the network frame is first dislocated assembled on the ground, then the whole network frame is lifted above the top of the column with a number of single-foot pulling rods, which are displaced in the air installed in the falling position.