Optimum seismic design of multi-story buildings for increasing collapse resistant capacity

The distribution patterns of equivalent static seismic lateral forces used in current structural design codes are mostly derived from elastic vibration modes. Such force patterns may not be consistent with actual conditions when structures behave into the inelastic range or even into the collapse stage. In this study, a new design method for multi-story buildings that uses an optimum lateral force pattern is proposed based on the concept of uniform damage distribution at the collapse state of these buildings. To reduce the computational cost of statistical analyses for deriving the optimum lateral force pattern, the non-linear story behaviors are represented by a story shear-deformation model with tri-linear relationships. Systematic parametric analyses are performed to study the influences of various ground motion parameters (site condition, magnitude, distance to rupture, and near-fault effect) and structural parameters (number of stories, fundamental period, damping ratio, post-yielding stiffness, ductility, and degrading stiffness) on the optimum lateral force pattern. Formulas for the optimum lateral force pattern that are applicable for practical seismic designs are provided. The collapse resistant capacities of structures designed using the proposed and conventional methods are compared by fragility analyses. Results show that the proposed method increases the seismic collapse resistant capacity of structures under the same construction cost.