Tensile Structure VS Conventional Structure
Conventional building structures, such as concrete, steel, wood or masonry, have two main properties: GRAVITY and RIGIDITY. It is these properties that make them stable and capable of transmitting load.
In tensile structure gravity and rigidity are not available as the critical structural properties, for they are so light and their components are often flexible. So to achieve stability and strength, their components require arrangement in a specific geometric form (surface shape), while being subjected to a specific pattern of INTERNAL STRESSES.
Case of A Clothesline
We could describe this through the case of a clothesline.
A clothesline with laundry will assume a smooth downward bow in response to both its own weight and the weight of the items of laundry. As long as there are no other forces acting on the system, it will stay this shape. If add a wet shirt in the middle, this shape will change, deflecting downward where the shirt is added, and flattening out at each side to retain its overall length and stay taut.
If there is wind, the situation will change dramatically: under gusty conditions, the clothesline will lose its initial shape, flapping up and down. During this process, our line will go through a slack stage, during which the stabilizing tensile force is lost.
Then the clothesline gets to a new taut.
Adding more weights could solve the problem.
Alternatively, the clothesline could be stabilized by adding a reversed cable on top, pushing down on the line with struts. But this is not enough, for the structure will simply flip sideways or invert. Stay cables anchored back to the tree will avoid this.
A reversed rope line below the main rope, with vertical strings connecting the two, is simpler and more effective. This is the most stable and the most sensible solution.
Cable Model
If we consider these two lines to be cables in a roof structure, and turn the lower cable by 90 degree to run across the upper one, we will achieve a stable point at their intersection.
Adding two more time-down cables parallel to the first will generate two more stable intersection points.
The additions of edge cables placed between the upper and lower support points begins to turn this arrangement into a two-way cable net that is completed by adding denser sets of cables, parallel to the original ones, in each direction.
We get a two-way cable net structure that has one unique characteristic: any two cables that meet at an intersection point, or node, are bent in opposite directions, one pulling downward and one pulling upward, thereby exerting pressure against each other. When we put this cable into tension, we increase the internal tension. The higher the initial tensions, or pre-stress level, the more stable and stiff the cable net system will become.
Outside Link to "Tensile Structure Design & Analyses"