Column Buckling Resistance - A Clue By An Aquatic Living

Isn't that amazing, when an aquatic living gives a clue on a theory behind a new concept for the resistance of building components against buckling?

As a part of research by the Brown University engineers, relating to the determination of shape that would help in increasing the buckling resistance of building structural components, lead to the study of an aquatic living named the "sea sponge", as shown in figure 1.
The study progressed with the realization of the sea sponge structure and the structure configuration within the living, that helps in maintaining the structure symmetry and their spherical arrangement under higher pressure. This ability is due to the presence of structural rods, with an optimal shape that would help the living to resist against the buckling pressure.
Fig.2. The spicules rods found inside the sea sponge

Structural Rods For Resistance

The structural rods are called as strongyloxea spicules, that have a length of 2mm and thinner than the human hair. These rods are in hundreds that are compiled together to form a rib-like structure, within the sea sponge body. The structural rod is tapered symmetrically, flatter at the middle and thinner at the ends.

Strongyloxea spicules compared with real column structures

With the help of structural mechanics models, the researchers found that this unique shape of the spicules can be found the optimum for the application to real-time slender structures, for buckling resistance.
Sponges are filter feeders -- they pump water through their bodies to extract nutrients and oxygen. To do this, their bodies need to be porous and compliant, but they also need enough stiffness to avoid being deformed too much.
The forces in each individual spicule were determined with the help of mathematical modeling. It showed that the rods are subjected to a single type of mechanical loading and that is the " compression load". The primary failure mode of the spicule was through buckling. bending starts at a critical point, which later moves to the point of highest bending value. This causes collapse.

Material for Resistance

The material that would help in the resistance against the buckling was determined with the help of a scanning electron microscope. The result showed the main composition was "silica- or glass". These were the elements that provide stiffness against the higher pressure of waves.

Optimal Shape

A study on the existence of any engineering column with a similar tapered structure like the spicule leads to the determination of " Clausen column". This concept was put forward 150 years back, by Thomas Claused. He proposed that the tapered columns (tapered at the ends) possess a greater buckling resistance compared tot the plain cylinders. A mathematician in 1960, Joseph Keller, also proved that the optimal resistance for tapered columns is 33% greater than the conventional column structure.The spicule model studied by the Brown University engineers too resembled with the Clausen column.

Engineering Lessons From Nature

This study showed that the nature selection figured out something that engineers have not. The Clausen column is not shown up in the community and has to face many challenges before its practice. This has a scope for future nanoscale truss structures. "This is one of the rare examples that we're aware of where a natural structure is not just well-suited for a given function, but actually approaches a theoretical optimum," said Kesari, an assistant professor of engineering at Brown.


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