Learning Seismic Design from the Earthquake Itself

Visiting an earthquake damaged town is like visiting a gigantic structural testing laboratory. A carefully conducted forensic engineering can reveal much insight on the nature of earthquakes and the fundamental principles of seismic design. The earthquake devastated area is sufficient proof that earthquakes release a tremendous amount of energy. This energy propagates in all directions and enters a structure as ground motion which has displacement, velocity, and acceleration components. The seismic energy which is introduced into the structure must be dissipated within the structure. Energy dissipation shows itself mainly as inelastic behavior of the structural system. The structure must be damaged to dissipate energy. If seismic energy is dissipated at locations which make the structure unable to satisfy equilibrium of forces, collapse is inevitable. An earthquake resistant structure should dissipate seismic energy as damage in the structural system, but collapse should not occur. What is more, after the earthquake, damage should be economically feasible to repair. Observations reveal that beam-column joints and column ends are wrong locations to dissipate seismic energy. Shear failures and anchorage failures of reinforcing bars are wrong types of damage which dissipate very little energy and lead to collapse. Short columns and soft or weak stories must be strictly avoided. Longitudinal and transverse reinforcement should be well detailed and anchored. A successfully designed and constructed building should contain shear walls conforming to the year 2000 requirements of the ACI. In the wide earthquake devastated area, observations reveal that no buildings have collapsed which contain shear walls as part of the structural system. Shear walls are the seismic collapse insurance of a building. A successfully designed and constructed building should not sway out of control, should dissipate seismic energy by flexural plastification at bottom of shear walls and ends of beams. The occurrence of shear failure before flexural failure should never be permitted.