What gives an engineer confidence to project and build something as large and graceful as the Golden Gate Bridge (the creation of late Purdue professor Charles A. Ellis), knowing that it has to withstand the demands of gravity, wind, and earthquakes? Why did Gaudi think of the Sagrada Familia “upside-down” before he started building it? Who decides how much reinforcing steel goes into a reinforced concrete column supporting 100 floors in a skyscraper? And how do they make that decision? How far apart can we place the supports of steel girders in our bridges?