Antifragility: One-Upping Resilient Design

Blaine Brownell

Antifragility: One-Upping Resilient Design

Blaine Brownell

2018, Architect

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Antifragility: One-Upping Resilient Design Is it possible to design structures that improve under environmental stressors? Blaine Brownell explores examples of antifragile building materials and systems. Located in San Francisco, Five88 by David Baker Architects is clad in CorTen steel. Mariko Reed/OTTO. Faced with an increasingly volatile climate, architects are in a defensive position—one that demands their designs prioritize resiliency, or the ability to limit damage and bounce back from adversity. But what if the focus shifted from rebounding to improving and developing strength from distress? Nassim Nicholas Taleb, author of Antifragile (Random House, 2012), calls this concept antifragility, or the phenomenon of gaining from disorder. “Antifragility is beyond resilience or robustness,” he writes. “The resilient resists shocks and stays the same; the antifragile gets better.” A common example is the use of vaccines that introduce small quantities of antigens to improve our bodies’ response to disease. Another is the practice of weight-training, which strains muscle tissue as a necessary part of gaining physical strength. Although the processes can be complex, the concept is simple: Taleb explains, “anything that has more upside than downside from random events (or certain shocks) is antifragile; the reverse is fragile.” When we look at most building products, they fall into the latter category. So, have we been constructing fragile architecture? Not entirely. Many materials have intrinsic antifragile properties. Metals like copper, aluminum, and zinc corrode rapidly to form “sacrificial” coatings of oxide compounds. However, these coatings protect the materials from further oxidation. In some cases, this process is intentionally enhanced, such as the anodizing of aluminum to increase the thickness of the oxide surface layer for even greater durability. Another example is weathering steel, such as Cor-Ten steel, a high-strength alloy that develops a sacrificial surface layer 1 Blaine Brownell ARCHITECT October 25, 2018 that protects the metal from further corrosion. In this case, the material reveals its past “failure” or “downside” as rust in the process of becoming more durable. Certain wood products exhibit a similar property with regard to fire protection. Heavy timber constructions—especially those with “smooth flat surfaces, assembled to avoid thin sections, sharp projections, and concealed spaces,” according to the Woods Products Council—form a protective char layer when burned, delaying further incineration. Without this selfpreservation capacity, the concept of tall timber buildings would never have attained practical fruition. Similar to oxidizing metals, this method can be accelerated, as evidenced by the growing popularity of the shou sugi ban method, a traditional Japanese technique of weatherproofing wood by intentionally charring its surface. On the more exotic side, several laboratory materials demonstrate the promise of antifragility. One is a liquid crystal elastomer developed in the Verduzco Laboratory at Rice University in Houston. Researchers discovered that this silicone material gains strength under pressure, increasing in stiffness by 90 percent when compression is applied. Another is a smart textile, Active Protection System, developed by Dow Corning that consists of fabric infused with a dilatant silicone coating, a shear thickening fluid. When the soft and flexible textile receives a substantial impact, the silicone immediately becomes rigid. Once the shock has passed, however, the fabric returns to its pliable state. Yet another example is a selfhealing plastic developed by chemical engineers at MIT made of aminopropyl methacrylamide and glucose with plant chloroplasts. The plastic continually absorbs carbon dioxide from the surrounding air, transforming itself into an increasingly durable, carbonized material over time. Not only does this capability epitomize the concept of antifragility, but it also represents a promising future for atmospheric carbon sequestration. Such material properties may be compelling, but what about building structures? After all, in the event of a natural disaster, it is more critical that a building remains standing than that its surfaces resist weathering (although this is undoubtedly a welcome benefit). Unfortunately, most building construction methods are either neutral or fragile, insofar as they demonstrate resistance to shock or weaken because of it—as opposed to gaining from stress. This reality is innate to how we speak about structures as "bearing" or "resisting" loads rather than welcoming external forces to increase strength. One way to achieve structural antifragility concerns the way tensile forces are addressed. “Our conventional buildings are designed to carry loads in compression,” explains DCI structural engineer Jinal Doshi in a Quora article. “So for an exact same section as you increase the load, it slowly deforms and suddenly gives up and buckles.” Yet tensional integrity 2 Blaine Brownell ARCHITECT October 25, 2018 Kurilpa Bridge, a $63 million pedestrian and bicyclist bridge spanning the Brisbane River, is based on “tensegrity,” the term coined by R Buckminster Fuller to describe the principle of balanced compressive and tensile forces. structures (nicknamed “tensegrity” structures by Buckminster Fuller) convey loads primarily via tension cables that are held apart by strategically placed compression members. As the tension load increases, the cables stiffen, thus increasing the stiffness of the overall structure. A similar phenomenon may be seen in the function of a spring-loaded camming device used in rock climbing: as tension increases on the handle, the cams’ connection to the rock face becomes stronger. Although the tensional integrity approach has been used in construction, such as in Brisbane’s Kurilpa Bridge or the roof of Atlanta's Georgia Dome, it is not a widely popular application. One reason may be its inherently dynamic nature. As different loads are applied to such a structure, it adapts readily by changing its shape. According to Doshi, a tensegrity construction “is continually failing—but it is failing in its entirety, so even a rather large force can cause only a rather small deformation.” Arguably, this response is favorable to that of a conventional compressive structure, which bears increasing loads until it reaches a catastrophic breaking point. In this way, attaining antifragility in architecture will require it to become more receptive to change, and thus more life-like. Just as natural organisms gain from disorder via dynamic responses, architecture may become similarly active—with visibly mutating surfaces and enlivened structures. Such an approach will require society to overcome deeply ingrained associations of buildings as static, unchanging objects. Yet with ever-more powerful storms looming on the horizon, how long will we maintain this outmoded conviction? 3 Blaine Brownell ARCHITECT October 25, 2018

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