Concrete Umbrellas Protect During Coastal Storm Surge

When a storm approaches the coast, it stirs up waves and wind. A row of oversized concrete umbrellas has been erected along the beach that is lined with a boardwalk. These umbrellas start to tilt downward, changing from a simple canopy to protect against the onslaught of the incoming storm.

In the latest approach to protect from a storm surge, researchers from Princeton University have made a preliminary design for such dual-purpose kinetic umbrellas. In a study recently published in the Journal of Structural Engineering on March 28^th, 2020, the team utilized computational modeling to assess the ability of the umbrellas to resist an intense storm surge.

As storms become stronger and sea levels rise, coastal communities are erecting more numbers of seawalls to ensure the safety of property and people from excess flooding. However, such barriers can be unappealing and limit access to beaches. Now, the umbrellas developed by the Princeton University team would offer shade during reasonable weather and could be bent ahead of a storm to create a flood barrier.

This is so much more than just your typical coastal defensive structure. It’s the first time that anyone has really tried to integrate architecture as an inherent component to a coastal countermeasure.

Shengzhe Wang, PhD Student and Study Lead Author, Department of Civil and Environmental Engineering, Princeton University

The umbrellas proposed by the researchers are essentially shells of reinforced concrete that measure approximately 4″ thick and made in the shape of a hyperbolic paraboloid (for hypar for short)—that is, a saddle-like structure that curves outward along one axis and inward along the other.

The structure of the umbrellas was inspired by the study performed by Félix Candela, the Spanish-born architect who designed scores of buildings that feature thin-shelled hypar roofs in Mexico during the 1950s and 1960s.

Maria Garlock, the co-author of the study and a professor of civil and environmental engineering, has long been studying Candela’s architectural designs; she jointly penned a book on Candela and helped in creating an archive and exhibition that investigates his work.

During the fall season of 2017, Garlock and Branko Glisic, the study’s co-author and an associate professor of civil and environmental engineering, respectively, were looking at a project to examine the ability of hypar umbrellas as “smart” structures to trap rainwater and energy. Then, she was struck with a new idea: Apart from adding sensors, “why not tip them and use them in a completely different way—as a kind of seawall?” she asked.

Both Garlock and Glisic received funding from Project X, which allows engineering faculty members to explore unusual ideas. Wang took the responsibility of testing whether the umbrellas would offer a practical method for coastal protection.

Wang subsequently inspected the structural strength and geometry of the suggested umbrellas, thin concrete shells measuring 8 m (approximately 26′) on both sides and supported by square columns measuring 20″ and 10′ in length. In these simulations, Wang also tested the functionality of a hinge located at the vertex, where the square column meets the center of the umbrella.

To find out how the proposed umbrellas are likely to fare during a coastal storm surge, the researchers compiled storm surge data collected from hurricanes that occurred between the period of 1899 and 2012 along the U.S. East Coast, and subsequently modeled a storm surge height of 18′, covering all but the highest storm surge in the data set.

Adapting already defined numerical techniques for modeling the interactions of fluid-structure to analyze hypar structures, the researchers demonstrated that the umbrellas would continue to stay stable when they encounter a water wall measuring around 75% of their deployed height.

These shells are so thin that anyone looking at this would not be inclined to believe that these structures would be capable of stopping such large forces from water. But we're able to take advantage of the geometry of the hypar shape that gives the structure the additional strength that’s required.

Shengzhe Wang, PhD Student and Study Lead Author, Department of Civil and Environmental Engineering, Princeton University

Now, Wang has constructed the physical models of umbrellas (measuring around 6″ across) to verify the numerical approach results, and is starting to test the reactions of the models toward the dynamic forces of turbulent flows within a water channel measuring 10″ long. Wind forces, typical of landfalling hurricanes, will also be captured through wind tunnel testing.

“In reality, you’re not going to just have a pile of static water. You’re going to have waves, you’re going to have wind that generates those waves,” Wang added. “That’s what we’re trying to capture in our next step: How do we physically simulate these waves and how would these waves affect our structures?”

Wang observed that a majority of earlier researches have assessed the potential of slanted barriers or vertical walls to tolerate storms; however, the intricate geometry of the hypar required the scientists “to come up with a whole new set of rules that govern how the structure will perform.”

Owing to the difficulty of the solution, Vanessa Notario, another graduate student, will analyze the flow of forces in the shell as a part of her M.S.E. dissertation.

Apart from improving the structures to withstand high waves and winds, coastal protection designs should also consider other viable solutions. According to Garlock, the 10-foot height of the columns is excellent for shading pedestrians while limiting access to the hinges of the umbrellas and preventing vandalism.

The researchers are planning to study the potential of utilizing more sustainable materials. They are also planning to add actuators and sensors to manage the umbrellas and incorporate the systems to capture stormwater and solar energy.

Sensors would verify that umbrellas are performing properly before, during and after deployment, while actuators would enable not only automatic deployment but also tracking the sun and wind for the best power and storm water harvesting purposes.

Branko Glisic, Study Co-Author and Associate Professor Department of Civil and Environmental Engineering, Princeton University

Glisic is also an expert in smart structures and structural health monitoring.

“This is a completely new way of thinking about coastal defense structures,” added Garlock. “Moving forward, our goal is to make these umbrellas part of a smart, sustainable community.”

To help incorporate the latest design into holistic plans for coastal resilience, the scientists will team up with Ning Lin, an associate professor of civil and environmental engineering at Princeton University whose research group has recently created the updated 21^st-century flood maps for the U.S. Gulf and Atlantic Coasts.

The researchers also intend to work with a geotechnical engineer and are seeking the advice of the New York City Mayor’s Office of Resiliency.

Apart from the Project X innovation fund, the study was partly supported by the Metropolis Project of Princeton University.