2415 Preliminary Planning Guidelines

In the preliminary stage of planning a space frame to cover a specific building, a number of factors should be studied and evaluated before proceeding to structural analysis and design. These include not only structural adequacy and functional requirements but also the esthetic effect desired.

1. In its initial phase, structural design consists of choosing the general form of the building and the type of space frame appropriate to this form. Since a space frame is assembled of straight, linear elements connected at nodes, the geometrical arrangement of the elements — surface shape, number of layers, grid pattern, etc. — needs to be studied carefully in the light of various pertinent requirements.

2. The geometry of the space frame is an important factor to be planned, which will influence both the bearing capacity and the weight of the structure. The module size is developed from the overall building dimensions, while the depth of the grid (in the case of double-layer), the size of cladding, and the position of the supports will also have a pronounced effect upon it. For curved surface, the geometry is also related to the curvature, or more specifically to the rise of the span. A compromise between these various aspects usually has to be made to achieve a satisfactory solution.

3. In a space frame, connecting joints play an important role, both functional and esthetic, which derives from their rationality during construction and after completion. Since joints have a decisive effect on the strength and stiffness of the structure and compose around 20 to 30% of the total weight, joint design is critical to space frame economy and safety. These are quite a few proprietary systems that are used for space frame structures. They should be selected on the basis of quality, cost, and erection efficiency. In addition, custom-designed space frames have been developed, especially for long-span roofs. Regardless of the type of space frame, the essence of any system is the jointing system.

4. At the preliminary stage of design, the choosing of the type of space frames has to be closely related with the constructional technology. The space frames do not have such a sequential order of erection for planar structures and require special consideration on the method of construction. Usually, a complete falsework has to be provided so that the structure can be assembled in the high position. Alternatively, the structure can be assembled on the ground, and a certain technique can be adopted to lift the whole structure, or its major part, to the final position.

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