Energy-based Capacity Spectrum

The nonlinear static analysis methods are a middle state between the linear static method and complicated nonlinear dynamic method. In fact these methods have been made to estimate strength and deformation capacities of structure and comparison these capacities with demands of performance levels. Selecting roof displacement as displacement control point in higher modes is one of difficulties and limitations available in nonlinear static analysis methods, so that in some structures such as typical structure SAC3, during constructing capacity spectrum curve for mode 3, because roof displacement isn’t proportional to displacement of other stories, with increasing base shear roof displacement decreases. One of proposed methods for removing available ambiguities in selecting roof displacement as displacement control point in nonlinear static analysis methods is use of energy-based capacity spectrum method not only magnitude roof displacement but effects magnitude and direction of roof displacement in determining equivalent one degree of freedom building model displacement are also considered. In this investigation results of different nonlinear static analysis methods obtained based on two separate concepts of energy-based capacity spectrum and conventional capacity spectrum (based on roof displacement) are compared together and with results obtained from nonlinear dynamic analysis. This research shows that results of nonlinear static analysis methods achieved by using of energy-based capacity spectrum have acceptable efficiently and accuracy in comparison with results of nonlinear static analysis methods obtained by using of conventional capacity spectrum (based on roof displacement).