Problems that should be paid attention to in the design of space frame structure (Part 1)

The space frame structure belongs to a branch of the space structure. It is a space structure composed of multiple rods connected through nodes according to certain rules. It can give full play to the advantages of three-dimensional force transmission in space, and is especially suitable for long-span buildings. In recent years, with the rapid development of our country’s economy, the application of space frame structure has become more and more extensive, not only in large public buildings, but also in industrial buildings.

1. Features of space frame structure

Compared with the general steel structure, the space frame structure has the following advantages:

1) It is a space frame structure system with a three-dimensional force transmission path, especially suitable for building roof systems with large spans and large column networks. Compared with steel roof trusses with the same span and column network, it has the characteristics of light weight, low cost, and good economic indicators;

2) With high rigidity and strong column deformation ability, it can meet the building requirements of large span and large space, and the seismic performance of the space frame roof system is also better than that of ordinary steel roof trusses;

3) The rods and nodes of the space frame structure are finalized and commercialized, and can be mass-produced in the factory, which can improve work efficiency. The on-site construction and installation are simple, the welding workload is small, and the splicing and installation of the space frame are not required. Large-scale lifting equipment, generally unskilled workers can carry out the construction and installation of space frame, with fast construction speed and short construction period;

4) The space frame structure is flexible in plane layout, beautiful in shape and generous. The roof is flat and regular, which is conducive to the ceiling, and the installation of pipes and equipment is also very convenient.

2. Form and classification of space frame structure The following types of space frame structures are commonly used:

1) An orthogonal space frame composed of plane truss systems, an orthogonal space frame obliquely placed, and an obliquely inclined space frame;

2) Orthogonal quadrangular pyramid space frame composed of quadrangular pyramids, oblique quadrangular pyramid space frame, checkerboard quadrangular pyramid space frame, star-shaped quadrangular pyramid space frame;

3) Triangular pyramid space frame composed of triangular pyramids, evacuated triangular pyramid space frame, and honeycomb triangular pyramid space frame. In general engineering, the space frame shape should be determined after a comprehensive analysis of the plane form, span size and load size of the project, surrounding support conditions and architectural design requirements.

3. Load analysis and design calculation of space frame structure

3.1 Permanent load

Including the self-weight of the space frame structure, the purlins and roof panels of the space frame roof. The self-weight of the space frame structure can be automatically generated by the computer, or estimated by empirical formulas. The self-weight of the roof covering materials, including the support strips and roof panels, when using profiled steel plates and thin-walled steel purlins，the value of the roof load can be 0.2 kN/m2 (single-layer slab) or 0.3kN/m2 (double-layer slab), when using other materials， it can be taken according to the “Building Structure Load Code” (GB50009-2001).

3.2 Variable loads

Includes dust loads, snow loads, wind loads, earthquake loads, maintenance loads and other live loads. When profiled steel plates and thin-walled steel purlins are used for the roof, the upper person is generally not considered, and the live load value of the roof is calculated according to 0.5kN/m2. If it meets the requirements of Article 4.1. 0.3kN/m2 calculation. The concentrated maintenance load is calculated by 1kN, the wind, snow and dust loads are taken according to the “Code for Building Structure Loads”, and other live loads, such as crane loads and suspended weights, are used according to actual conditions. Earthquake loads are calculated according to relevant seismic fortification regulations.

3.3 Principles of Design Calculation

The materials of the space frame structure are all considered in the state of elastic force, without considering the nonlinear properties of the material, the basic assumptions of the calculation are as follows:

1) The nodes are all hinged, and the rods only bear axial force;

2) Calculation according to small deflection theory:

3) Analysis by elastic method.

The space frame structure can use different methods to calculate the internal force and displacement according to the size of the span, the type of space frame and the actual situation of the project.

 1) Space truss displacement method, suitable for space frame calculations of various types and various support conditions:

2) The difference method of the cross beam system can be used for the calculation of the space frame composed of planar trusses with a span of less than 40m or the square pyramid space frame:

3) The quasi-sandwich plate method can be used for the calculation of space frames composed of plane truss systems or pyramids with a span of less than 40m;

4) Imaginary bending moment method, which can be used for the calculation of oblique square pyramid space frame and checkerboard square pyramid space frame;