Fazlur Khan seemed an unlikely candidate for engineering stardom. The tallest structure in his hometown of Dhaka was fewer than three stories high. He didn’t see his first skyscraper in person until he was 21 years old. In fact, he likely had never even stepped inside a mid-rise building until he moved to the United States to study structural engineering at graduate school. But Khan, the son of a mathematician, proved to be a civil engineering wunderkind. He received two master’s degrees in just three years.
At the University of Illinois, he studied under Hardy Cross, a legendary engineer who taught Khan not to see buildings as concrete monoliths, but as living things. Cross had a mantra: “You must learn to think as the structure thinks.” Many ridiculed Cross’s ideas, writes Khan’s daughter, Yasmin, in her book Engineering Architecture, but Khan took the advice to heart.
“I put myself in the place of a whole building, feeling every part,” Khan said in an interview with Engineering News-Record. “In my mind I visualize the stresses and twisting a building undergoes.”
Khan preached “structural empathy,” believing that buildings should absorb stress and react accordingly. If someone pushes you in the chest, your ribs alone don’t prevent you from falling—your stomach clenches, your calves brace, and your heels dig into the ground. The pieces work in tandem. The same went for skyscrapers.
When Khan and his friend and design partner, architect Bruce Graham, sat down to design the Hancock Center, the architectural world was in the midst of a break from skyscrapers. “Conventional” skyscrapers like the Empire State Building had proven prohibitively expensive. The higher a building, the more weight is exerted from the top. The building must also withstand winds, and these forces—downward and lateral—turn skyscraper construction into a riddle. A lot of steel and concrete is needed to keep a super-tall building standing, and all that material shrinks usable open space, riddling floors with dark, labyrinthine corridors. If you don’t have floor space to sell, what’s the point of making a building tall?
Khan had a solution. A few years earlier, Graham had asked him what the most economical building would look like. Khan replied, “A tube.” Like the bamboo that sprouted around Dhaka, a hollow tube lent a high-rise vertical durability.
Graham and Khan put the theory into practice while constructing Chicago’s 42-story Dewitt-Chestnut Apartments. The building was supported not by an inner grid of concrete and steel, but by its facade. Structurally, it had more in common with a grain silo than a traditional skyscraper—but it worked. The duo now had the blueprint for pursuing more ambitious structures.