Modern humans have been around for nearly 300,000 years, but even today, nature continues to surprise and inspire us. From bullet trains to airplanes, almost everything we have invented is influenced by elements found in the natural world. A recent example of this is a newly proposed building system that prevents the building’s total collapse, which takes its inspiration from lizards.
A building can collapse due to natural calamities, design flaws, vehicle impact, and any number other reasons. However, what’s more important to consider is how these buildings collapse and what damage this inflicts. Over the years, such collapses have costed many lives, and caused injuries, economic disruptions, and environmental damage.
“Disasters recorded from 2000 to 2019 are estimated to have caused economic losses of US$2.97 trillion and claimed approximately 1.23 million lives. Most of these losses can be attributed to building collapses,” the researchers note.
But what if, instead of catastrophically crumbling completely, a building could separate itself from the part from where the collapse initiates, similar to how a lizard sheds its tail to escape when a predator catches it?
“In such a way, we can save the remaining part of the building and ensure evacuation and rescue operations can be carried out there. This would allow us to save lives that would otherwise be lost if the building completely collapsed,” Jose M. Adam, one of the researchers and a professor of civil engineering at Valencia Polytechnic University (UPV), told ZME Science.
Problem with the current building collapse system
Buildings often seem to collapse all at once during a calamity. But, if you slowed time down, you’d notice it all begins with a small initial failure that continues to propagate throughout the structure. Modern concrete buildings are usually designed such that the sections are strongly connected together. This is to evenly distribute stress.
Such an approach has been proven to work effectively at dealing with small initial failures. However, it can backfire in scenarios involving large initial failures, causing the entire structure to collapse. This is because the connectivity introduced within the system can cause collapsing elements to pull down parts of the building that would otherwise remain unaffected.
“The fact that we are not considering this risk in the current building is quite alarming, and this becomes the starting point of our research in developing the collapse isolation technique,” Adam said.
In their new study, the researchers propose a new approach called “hierarchy-based collapse isolation”. It involves a system that will arrest the propagation of a major initial failure by ensuring that only specific elements of a building fail before the collapse reaches the most critical structural components.
The science behind lizard-inspired collapse isolation
Gecko tails are quite unique in the animal kingdom. They remain fully connected to the rest of the animal’s body for all normal functions. However, if a predator traps it, a gecko can perform an oscillatory bending motion which breaks off the tail.
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In other words, the tail is somehow designed to be well connected to the rest of the body for specific actions (or loads) and to separate when under the effect of other actions. The proposed collapse isolation technique for buildings works similarly.
It makes an important distinction between two types of initial failures. For the first type, referred to as small initial failures, the isolation system ensures sufficient connectivity to accommodate operational conditions by redistributing load, preventing further failure propagation.
For the second type of initial failure, referred to as large initial failures, the lizard-inspired approach aims to achieve two main goals: first, to stop the spread of collapse, and second, to enable the building to find alternative load paths (ALPs). This is done by prioritizing a specific order of failures among the components at the edge of a collapsing area.
“A specific mechanism will be triggered at the connection level to separate the collapsing parts from the rest of the building when the initial failures are too large to contain,” Adam told ZME Science.
This ensures the remaining structure of the building remains intact, allowing enough time for evacuation and rescue efforts.
Testing the hierarchy-based collapse isolation system
Jose Adam and his colleagues conducted an interesting experiment to test their proposed collapse system. They constructed “a real 15 m × 12 m precast reinforced concrete building with two 2.6-m-high floors.” This building was designed as per the lizard-inspired collapse isolation system.
Once the building was ready. They deliberately introduced small and large failures in the building to see how it would react. For instance, in the first phase of their experiment, they removed two columns to simulate a moderate failure.
However, the building didn’t collapse, showing that their design could redistribute the load and prevent collapse through the continuity provided in the beams, slabs, and beam-column joints.
“In such a way, we proved that our approach is consistent and compatible with current robustness standards adopted in practice,” Adam said
In the second phase, they removed a third column triggering a large initial failure. This time, the building partially collapsed, but their safety system stopped the collapse from spreading, saving most of the building.
“Thanks to the implementation of the hierarchy-based collapse isolation, the collapse front was arrested just at the borders between the initially affected regions and the rest of the system. Consequently, the collapse was isolated, saving the parts of the building located outside of the affected bays,” Adam added.
The future of lizard-inspired collapse system
For now, the proposed collapse isolation technique can only work for new buildings and cannot be applied to existing structures.
This is because the technique controls the hierarchy of failures in a structural system. So, it is more practical for engineers to apply it when the design of different building components can still be modified and adjusted to fit this approach.
“We are currently working on another project, the so-called Enhance, where we are developing a novel approach for retrofitting existing buildings by hanging floors from the roof of the building,” Adam told ZME Science.
Another big challenge with this approach is that implementing it in practice involves assessing multiple possible failure scenarios, which involve high-fidelity simulations that are not commonly used.
“In this regard, we are working towards developing more simplified design procedures to facilitate the design process. We hope this will raise the technology readiness of solutions for arresting collapse propagation, leading to more resilient buildings and positive societal impact,” Adam added.
The study has been published in the journal Nature.
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