Support locations

The choice of the most advantageous support locations will, of course, depend on the plan form of the structure. Depending on the grid configuration, it is possible to support either top or bottom node joints. Alternative support positions for a square plan, square on square offset-grid roof structure, supported at the upper node joints, are shown in Figure 8.2(a)-(d).

The provision of continuous edge support, as in Figure 8.2(a), is a more economical method of support for the space grid than just corner supports, as in Figure 8.2(b). This is because the maximum forces in the space frame and its deflections are less when the

8.2 Typical support locations for space frames

(b) Corner only

(d) Mid-edge only

(d) Mid-edge only

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(e) Random supports wyw_wvw_vwwy A A

(f) Inverted pyramid column supports (g) Top pyramid column supports supports are continuous. Intermediate supports along each edge, as in Figure 8.2(d), may also produce an efficient support system. In this case, some of the bottom-layer members will be in compression and some of the top layer will be in tension. To reduce deflections still further, the supports can be brought in slightly from the edges of the space frame to produce a cantilever portion around the whole structure. This can be useful architecturally as it allows the opportunity to have apparently column-free elevations.

An alternative method is to use 'tree' supports instead of individual columns. Commonly, this is achieved by inverting a grid module (e.g. a pyramid) at each support location, as the grid is then supported on several nodes at each column location, which reduces the forces in the bracing members at the supports. Irregular plan-forms can be created using modern analysis techniques, although the fabrication costs will be higher if more irregular member lengths and sizes are required.

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