Large-span bolted ball space frame structure construction technology

Combined with the Tianjin Light Rail Leisure and Entertainment District station space frame project, it introduces in detail the installation of large-span bolted ball node space frame structure and construction precautions.

1.Project overview

Tianjin light rail space frame project is a key project in Tianjin, in which the total construction area of the recreation area station is 3390m2, the station is 120m long, for the frame shear wall structure. Roof frame for the square quadrangular cone bolt spherical space grid structure, the top of the large roof frame for 90m × 47.5m rectangular, 28 diameter 1.2m columns distributed on both sides of the platform, the top of the 28 supports to support the entire roof frame. The axial plane size of the rack is 90m×47.5m, and the height is 1.5m. The total weight of the rack is 100.4,t. The total number of nodes is 1128, and the total number of rods is 2464.

2.Roof structure form

Tianjin Light Rail Leisure and Entertainment District station space frame roof is flat plate shape, and the roof frame adopts orthogonal space truss structure system. The main trusses are arranged perpendicularly and transversely in the direction of the line centerline, and are supported on 28 supporting steel columns of 10.3m height. The roof trusses are supported on 28 supporting steel columns with a height of 10.3m. All the roof trusses are made of hollow round steel tubes, and the nodes are connected by bolts and balls with direct intersection of coherent lines. The overhanging part around is inverted triangle space truss structure, the overhanging length is 3.8 m. The whole roof frame is supported by 28 curved bearings, and the nodes at the bearings are bolted ball nodes, and the bearings use metal spring anti-seismic bearings. space frame four slope arch, arch height of 150mm.

3.Project characteristics and difficulties

Roof rack space frame structure is a space structure composed of longitudinal main truss, cantilevered truss and support. In the process of assembling at high altitude, the stress condition of each member before the installation of roof tie rod is different from the design stress condition, and the main working condition in the construction process needs to be calculated and approved. Due to the large span, large weight, large size of the components of the space frame project, in the assembly and assembly process of stiffness, stability, deflection, internal force of the rods, etc. to be calculated for the construction, if necessary, need to take reinforcing measures. Due to the space frame project component length and section size are larger, the overall connection must be carried out at the site, which requires the construction organization, factory production scheduling, component transportation scheduling and other issues to be organized to ensure that the site smoothly assembled. Controlling the sinking amount of the roof frame is one of the difficulties in this project. The roof frame installation needs to be calculated according to the installation program to meet the working condition after removing the temporary support, so that the working condition internal force is close to the design internal force of the roof frame at this stage. The deflection value of the center point should be less than 19cm after removing the support after the installation of the roof frame materials.

4.The main construction method of space frame

4.1 Hollow steel ball and steel pipe rod production

In order to ensure the installation quality of the space frame, all hollow steel ball nodes and steel pipe rods are centrally processed in the factory. Steel ball using tire film processing, raw materials for 45 steel. Using a lathe cutting edge, processing allowable tolerance: diameter deviation ± 1mm, ball ellipticity deviation of 1mm. steel pipe rod length allowable deviation of ± 1mm, rod end face and rod axis must be perpendicular to the allowable deviation of 0.5% R (R for the radius of the steel pipe), the maximum bending of the steel pipe rod shall not be greater than 1/1000 rod length.

4.2 Installation of steel space frame

Computer simulation theory as the basis and guidance, developed a detailed assembly program. According to the structural characteristics of the project and the construction site layout, set up scaffolding platform on the ground, laying planks on the scaffolding, and then assembled on the scaffolding platform space frame, space frame assembly using air bulk method of construction.

According to the actual situation of the structure of the space frame and the left-right symmetry of the characteristics of the space frame, in order to reduce the space frame in the assembly project in order to minimize the accumulation of errors, the overall space frame assembly should be started from the starting unit between the 8-axis, 9-axis, start, and the space frame should be installed on the ground, in order to minimize the accumulation of errors. In order to reduce the accumulation of errors in the assembly project, the whole space frame should be assembled from the 8-axis of the starting unit to the 9-axis of the starting unit, and the vertical and horizontal axes of the starting unit should be assembled first, and the dimensions should be corrected at any time. During the assembly process, the bars will be lifted into place by the bailing bar, and the assembly will be bolted at the designed position.

4.2.1 Assemble the construction platform

First of all, the original ground for foundation treatment, to confirm that can meet the requirements of the bearing capacity and then set up scaffolding construction platform, the top surface using 1cm thick planks paved, the platform plane size should be larger than the space frame 1m or so, the top elevation of the construction platform should be lower than the lower layer of the space frame elevation of 300mm.

4.2.2 Starting unit assembly

Directly single rod, a single node assembled into a space frame, in the assembly process, the position of each node should be measured and double-checked. Starting unit of the space frame installation is completed, immediately after the self-check to ensure that all the nodes at the bolt fastening in place. Positioning welding (each support welding 3 points), to ensure that the space frame in the back of the installation process does not produce displacement. Then the starting unit as the center of the two directions at the same time assembled.