TITLE Capacity spectrum method for seismic design of a building INTRODUCTION The capacity spectrum method is a practical method to evaluate building responses under earthquakes. Input earthquake ground motion is defined by a response spectrum. Since both force and deformation are important for nonlinear analysis, the spectrum is plotted in acceleration vs. displacement domain which is termed as a demand spectrum. Seismic performance of a building is examined by nonlinear push-over analysis using a certain distribution for horizontal static loads. The relationship between base shear force and top displacement is plotted in acceleration vs. displacement domain which is termed as a capacity curve. The response of the building is then obtained as a crossing point between the demand spectrum and the capacity curve.     USAGE MANUAL See Reference 1). EXAMPLE See Reference 1). REFERENCE 1)      ATC 40 “Seismic evaluation and retrofit of concrete buildings”, ATC, 1996