Fabric Structure Forms: Mast-supported Structures

By Samuel J. Armijos, AIA

Mast-supported structures are membranes of one or multiple peaks supported by interior and perimeter masts or adjacent buildings. They most resemble a tent in form and use the least amount of structural material to construct. A bale ring, cable loop or top plate connects the fabric to the interior masts, while perimeter masts support the fabric by means of membrane plates. These perimeter masts are either designed as moment connections or with tie-downs. Some mast-supported structures do not have perimeter masts but rely on outriggers or structural members that cantilever off central masts, much like an umbrella.

The peaks of a mast supported structure can vary in shape and size depending on the overall design, method of attachment and structure under load. They tend to have round, oval or elliptical openings which are covered or left open. The membrane is normally patterned with seams radiating from the top of the opening. These triangular panels require more complex patterning, more seams and are less efficient in the utilization of fabric which is manufactured in long rectangular rolls. For small scaled projects and structures with multiple panels, seam orientation can be redirected to optimize material.

Most mast-supported structures can rely on the fabric’s structural characteristic without the need of additional support, but as these structures get larger, radial cables are required. In addition, as a precaution, safety cables are installed above the membrane from mast to mast and to the ground so that in the event the membrane fails, the mast will stay erected.

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