Shell is one of the strongest structures available in the nature. The nature generally relies on shell structures to protect the eggs and seeds for reproduction. The shape of the natural shells are optimized to carry the expected loads and mechanisms. Most bird eggs having an oval shape are one end rounded and the other more pointed. Load carrying capacity of an egg in the direction of major axis is much higher than in the direction of minor axis.
How do we think about a coconut falling from the tree to a sandy beach? Or the shell (hull) of an ocean going ship? Or the fuselage of an aircraft flying at a high altitude?
Being motivated from nature, engineers adopted shell as one of the basic structural forms for long span structures. The architectural elegance is maintained together with the material economy and enhanced load carrying capacity.
It is a challenge for us to analyze the shell structures. Shell elements in finite element technique can give you a reasonable result but perhaps a rational analysis can be performed if we can also consider the geometric and material nonlinearities. In BUET, we have mastered the method of analysis based on finite elements and developed design principles for helicoidal shells, paraboloids and hyperboloids.