Direct inelastic earthquake design using secant stiffness (local deformation control design)

A new earthquake design method, Direct Inelastic Design (DID), was developed. Existing inelastic design methods use nonlinear step-by-step analytical technique, and generally control overall ductility of a structure, which is not directly related to the safety of each member. On the other hand, the DID can directly determine the inelastic strength and deformation demands of the potential plastic hinges at each member, by using linear analysis for secant stiffness. In the proposed method, inelastic performance point of the potential plastic hinge is controlled to belong to the admissible zone which is specified according to the design strategy intended by the engineer and/or current design provisions. By restraining plastic deformation of the plastic hinges, the structural safety of each member can be secured. The earthquake design strategy intended by the engineer, such as the concept of strong column-weak beam, can be directly addressed. For a design example, a typical reinforced concrete building was designed by the DID. The result showed that by applying the design concept of strong column-weak beam, flexural damage of the columns was prevented and plastic hinges of the beams were distributed along the building height. The design results of the beams and columns, and the overall response of the structure were presented and discussed in detail.