Adrian Bejan | Columns and Skeletons, from Design in Nature
The video follows beams, columns, trusses, and skeletons from dried mud and fired brick to iron bridges, skyscrapers, and concrete, and shows how shape, weight, and buckling decide what survives. Concrete is stronger in compression than in tension, so steel-reinforced concrete places steel rods where the tensile stresses live. The drawing matters because the lightest structure comes from eliminating what is not stressed and keeping only what works. From the balcony crack to the skeleton of the Statue of Liberty and the Eiffel Tower, the same view repeats in nature and in man-made structures. The forest adds wind and water: vertical parts bend in the wind, and everything that grows on land pumps water upward, so flow and support belong in the same drawing.
Concrete resists compression better than tension, so a beam snaps where the upper fiber in tension reaches the maximum allowable stress, which is why a crack on an old balcony appears near the fixed end. Steel-reinforced concrete places longitudinal steel rods near the surface that carry most of the tensile stresses, and the cross section allows more metal where it works and less where it does not.
The drawing is a way to decide where to keep material and where to remove it. The rule is to find the piece that is not stressed and eliminate it, which explains why trusses look open, why the inside of the Eiffel Tower looks like a lattice, and why the skeleton of the Statue of Liberty carries load with little wasted material.
Columns and skeletons show that a few supports that do not buckle can be better than many skinny ones. A three-part shape with a trunk and two legs teaches that the V or great lambda is a good way to carry weight, and that the proportion of torso and legs can be read from buckling limits.
Bigger things require bigger cantilever parts, and cheaper materials make them possible. Antiquity used dried mud; the Roman Empire used fired brick; the spread of iron bridges led to taller buildings; and concrete made columns, beams, and skeletons on a large scale, provided their shapes respected bending and buckling.
The forest shows vertical parts embedded in the ground that are blown from the sides by the wind and bent, while everything that grows on land pumps water upward into the dry wind. Animals go to where the water is and act as water trucks, so support and flow are joined in one picture.