“O Lord my God, you are very great!
You are clothed with splendor and majesty,
covering yourself with light as with a garment,
stretching out the heavens like a tent.” – Psalm 104, 1-2 ESV
Ultimately, the joy of studying textiles and working with fabric applies to my interest in structures — whether handbags or buildings. Fabrics are incredibly flexible, and their wear strength and shear strength are phenomenal. This comes from the shared load of tension across more than one direction.
“Fabric,” of course, includes any woven material, not just wool, cotton, and clothing materials. While we generally think of fabric as a plane, it can be woven zig-zags, trusses, etc. as well.
Simple fabric weaves, like the woven plastic straps that create a lawn chair, transfer loads in two directions. Straps of fabric go both side to side (weft) and front to back (warp.), Wherever you sit, your body weight is carried in both directions. Not only that, but the tension becomes a compression on the next piece of plastic, which then translates to the tension on that next strap. In other words, the load transfer is not linear, but bidirectional. As this bidirectional shift in loads occurs, the weight transfer continues to travel, creating a virtually circular distribution that ultimately extends to the very edges.
This non-linear aspect of fabric results from changes in geometry that occur under load, even though the materials remain linearly elastic.
This change in geometry creates a wonderful quality. If properly designed, the load bearing capacity of stretched fabric increases to carry loads as the fabric deforms. In fact, these structures are capable of maintaining a very high ratio of applied loads to self-weight, in contrast to steel, concrete. or other rigid structures of the same spans.
Make no mistake. The design possibilities are enormous to an almost ridiculous level, and perhaps even more surprising, the engineering limitations are virtually non-existent. It is almost a safe statement that the engineering possibilities in the mechanical, structural, design, appearance, or textural use of fabric are limitless! (Imagine tapping into the “fabric of light” and “stretching the heavens as a tent”! While that is God’s domain, we probably have a taste of it available to us.)
The primary challenge of using fabric is the relatively quick decay of materials used, meaning that fabric, while incredibly strong and flexible, has to be replaced quite often. The decay results primarily from UV radiation and from the extremely high surface area of the fabric to thickness. By nature, fabric is made of individual strands, woven into a moderately solid sheet. Every “thread” is almost completely and thoroughly exposed to decay factors. Decay results in significant changes in the fabric. Loss of tensile strength, flexibility, and shear can be catastrophic.
To me, this calls for a very simple (in theory) solution: Better fabric materials! By combining the use of surface coatings, shifting the insulation to the exterior and the interior, and adding a second layer of “roof” or external covering to absorb the UV and atmospheric gases can protect the fabric from corrosives by simply reducing contact, etc. It may also be possible to create the fabric assembly to be suspended in a very light hydraulic fluid or inert gas so that it can be repaired or replaced by simply sliding out the old or damaged section without significant disassembly of the entire structure.
Of course, fabric is only useful in tension, not compression, but consider how this could be resolved by massing fabric into compressive bundles like bolts of fabric, stiffened by . . . tension! — pulling the fabric very tightly around itself, or around a rigid core, increasing the compression to take advantage of its greatest asset, namely, using tension to form a compression reaction in opposition. The resulting posts would have all the tensile characteristics of fabric, making them almost infinitely flexible while providing tremendous strength from the non-linear tension holding them.
This is not an essentially novel idea – just not fully implemented. Fabric has been with us forever. It is suggested in the nature of steel reinforced concrete, where steel grids and cables add the tension that concrete lacks, and concrete provides the compression resistance that can limit steel. It is also used for some domes and other roof structures. Converting steel cables to interconnected fabric would solve all the existing problems in current practices of pre- and post-stressing concrete.
Another great benefit of such innovation is weight reduction. If a structure that requires 100 tons of concrete, say, were reduced to a comparative weight of 20 tons, and gained the flex and load distributing properties of fabric, you could theoretically gain an additional 80 tons of support and load capacity for the contents of the structure without an overall change in weight. Improved stability and flexibility of a fabric foundation, and the use of adjacent structures (primarily roads, sidewalks, and parking lots) as part of the fabric foundation in building design would bear weight normally transferred directly to the ground structures directly beneath a building or other structure.
One final note on fabric as a building material is cost. Steel and concrete are reasonably cheap. Way outside of my capacity, however, are cost estimates over time. If load capacity, stability, duration, safety and design can be improved or “solved,” we are in a solid position to make headway and some needed change.
Consider that the last 30 years have yielded an increase of triple the number of deaths from natural disasters. We have witnessed structural failure and loss of service to buildings and other structures like towers, dams and bridges (meaning displacement and isolattion of populations, loss of production, storage, utilities, communication, transportation and services.) If fabric construction can end or significantly reduce these problems, then building costs plummet.