Japanese seismic design codes prior to Hyogoken-Nanbu earthquake

A large number of concrete bridges were damaged by the Hyogoken-Nanbu earthquake. Many of these bridges were found to have crumbled after suffering shear failure. This indicates that the original seismic design of these structures was inappropriate. Bridges that did not suffer shear failure, however, generally survived collapse even if they were severely damaged by bending moment. It has been confirmed that concrete structures do not actually collapse if they have sufficient resistance to shear failure, even if the displacement they experience is far beyond the bending yield displacement. This justifies the latest seismic design methods, in which collapse under the influence of extreme seismic motion is prevented by making the resistance to shear failure adequate enough to ensure the survival of each member. These latest seismic design codes and the changes in the codes are described.