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distance it can span for a given load, all other factors being equal. For example, the model |
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of unit cell c) should be able to span twice the distance or carry twice the load of unit cell |
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a), because c) has twice the depth as a) but the same module size. Consequently the depth/ |
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module ratio of c) is twice that of a). As a result the diagonal struts of cell c) are aligned |
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more parallel to a perpendicularly applied load. This reduces the internal stresses its web |
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struts are subjected to. However, as with truss bridges, there is a limit to how deep a double |
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layer spaceframe lattice can be before other factors such as the slenderness ratio of the |
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struts, the dead weight of the structure, and its cost must be taken into account. Note also |
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that when the depth/module ratio of a Tri-1 unit cell is equal to 0.816, all of the struts of the |
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spaceframe are the same length. That is, it is a standard octet truss. |
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. |
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Another factor affecting the load bearing capacity of a spaceframe is how its perimeter is |
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supported. In general, the more support that is given to the spaceframe's perimeter, the |
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longer it can span, and the greater load it can carry, all other factors being equal. For |
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example, for a given load, the required depth to span ratio for a spaceframe entirely |
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supported around its perimeter is about one-half of that for one that is just supported at its |
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corners. |
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. |
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. |
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This is due to the fact that the maximum bending moment exerted by a load located mid- |
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span of the structure is a function of its distance from the nearest support, as you saw before |
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with beams and truss bridges. Supporting the entire perimeter of the spaceframe reduces |
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this distance overall compared to just corner supports. |
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. |
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The Tri-1 spaceframe is a very efficient design due to its omni-triangulated geometry that |
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minimizes material usage while maximizing its surface area. It is particularly appropriate |
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for maximum load bearing situations. |
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. |
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. |
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Variations of the Tri-1 spaceframe design are generated by selectively removing struts from |
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the structure in a regular pattern. Two common examples are Tri-3 and Tri-5. |
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| . | |||
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Back to Knowhere |
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