Rigid Support Frame in Installation and Construction of Long Span Space Frame (Part 2)

2.1.4 Site requirements

1) Site flatness requirements. If full hall scaffolding is used, the site needs to be leveled; if the sliding operation frame is used, the site needs to be leveled, requiring full hardening of the site; if rigid support frames are used, the site needs to be leveled, requiring partial hardening of the site.

2) Site occupancy requirements. Using a full house of scaffolding, the construction site will be fully occupied by scaffolding. Due to the large construction area of the space frame and the variety of material types, the space frame components will not be able to be placed reasonably; the use of sliding support frames will take up 2/5 of the space. The construction site, the effective construction site is squeezed; the use of rigid support frames occupies a small area of the site, and the effective construction site can basically be used entirely, and when the placement of components conflicts with the rigid support setting, it will hinder the setting of rigid support components Just remove it. Therefore, for the comprehensive applicability of the site, it is more reasonable to use a rigid support frame.

2.1.5 Construction efficiency

1) The use of full-scale scaffolding or sliding support frames for construction will result in a significant reduction in construction efficiency. Before the space frame is assembled, the bolt (welding) balls, rods and accessories must first be moved to the support platform by a crane, and then translated and transported manually, which is inconvenient to operate. During the assembly of the space frame, due to the large height difference between the upper string and the lower string (2.5-4.8m), when installing the upper string ball and the web bar, the crane cannot be used, and the winch can only be used for hoisting.

2) The use of rigid support frame construction is not limited by the platform. Ground transportation uses forklifts or rubber wheels; the space frame is assembled on the ground and then hoisted in place by a crane (or lifting equipment); the high-altitude bulk parts can be assembled into a triangular cone on the ground, and then the cone is directly hoisted to the installation position by a crane. To sum up, for the installation of large-span space frame projects, the use of rigid support frame construction can obtain better comprehensive benefits.

2.2 Construction characteristics of rigid support frame

1) The rigid support frame is easy to install, adjust and remove. The height adjustment system of the rigid support is set at the bottom of the column, and each height adjustment system is equipped with 4 sets of supports, which are composed of limit rings, mechanical jacks, and steel bottom plates (Figure 2). The limit ring is fixed on the bolt ball at the bottom of the column with bolts to prevent the jack from slipping out of the support surface; a steel bottom plate is placed under the jack, and a sand and gravel leveling layer or a concrete cushion is placed under the steel bottom plate. When the ground on site is relatively soft, it can be dealt with by enlarging the size of the steel base plate and reducing the pressure to prevent the support from settling. The jack is mainly used for height adjustment. When the height of the jack is not enough or the amount of adjustment is insufficient, steel plates and short pipes can be added to the bottom of the jack to assist in height adjustment.

Figure 2 Rigid support frame height adjustment system

2) The rigid support frame can be recycled. When the space frame is installed to cover the civil concrete support and the support rod is installed, the rigid support installed first can be unloaded, removed, and recycled to meet the green construction requirements advocated by the country.

3) The rigid support frame can be set flexibly. The cross-sectional size of the rigid support frame of this project is 3m×3m, which is consistent with the grid size. Its 4 support columns and any adjacent 4 sets of lower string balls of the grid frame can be seamlessly connected by high-strength bolts (Figure 3). Theoretically, the rigid support can be placed anywhere under the projection surface of the grid, which can avoid obstacles such as equipment foundations and foundation pits in the building.

Figure 3 The rigid support frame is connected to the space frame

4）Occupies less construction site. The occupied area of a single rigid support frame used in this project is only 9m ² . Based on the calculation of the anti-collision fence around the support, each support frame occupies an area of 25m ² , and the total occupied area is less than 7% of the construction site.

5）Meet local concentrated bearing capacity requirements. The largespan space framestructure has a large area and a long slope, and the roof panels generally can only be pressed on site. If it is pressed on the ground, it is more difficult to hoist to the roof because the roof panel is too long. When rigid support is adopted, the press machine (7-10t) can be placed directly on the roof for operation without being limited by the load of the roof.

6) High degree of stability. The setting of independent support should not only have sufficient support and stability, but also have a certain ability to resist accidental force collisions. In the process of engineering application, there was an accident in which the rigid support was accidentally collided by the construction crane on the site. One of the four-leg supports was crashed, the rods were bent, and the bolts were broken. But the other three limbs were safe and the overall stability was not affected in any way.