The secret of the swaying columns
Completed in 1420, the Forbidden City is the world's largest collection of preserved ancient wooden structures. For 600 years, its nearly 1,000 buildings have survived fires, weather, and at least 200 recorded earthquakes, including the devastating 1976 Tangshan earthquake. The structural resilience comes from a sophisticated system of joinery that uses no nails or glue in its main supports. The main element is the dougong, an interlocking wooden bracket that connects the tops of columns to the massive roof beams.
This design allows the structure to behave more like a flexible skeleton than a rigid box. During an earthquake, the mortise-and-tenon joints of the dougong can flex, shift, and rotate. This movement absorbs and dissipates huge amounts of seismic energy through friction. The main structural columns, crafted from whole logs of precious Phoebe zhennan wood, are not anchored into their stone plinths. Instead, they are designed to rock and shift on their foundations, preventing the columns from snapping under stress. The heavy, ornate ceramic tile roofs, far from being a liability, press down on the frame, adding a stabilizing weight that helps reset the joints after the shaking stops.