The Pushover is a static nonlinear analysis in which the structure is pushed gradually following a predefined load pattern distribution. Material nonlinearities in structural elements are usually modeled by concentrated plastic hinges and the option for including geometrical nonlinearities is available.
A control node, generally located at the top level of the structure, is considered to monitor the lateral displacement while the load is increased. The base shear is plotted Versus the control node lateral displacement and the resulting graph is called the Pushover curve.
The pushover curve represents the structural capacity to resist lateral loads and for this reason it is also called the capacity curve. On the other hand, the adequate seismic response spectrum represents the seismic demand and is also referred to as the demand curve.
The purpose of the pushover analysis is to determine the maximum structural nonlinear response to seismic loads. This extremum is provided in the form of maximum control node displacement. Then, based on its value, the location and plastic limit state of hinges are determined and the inter story drift is checked.
The sought maximum response is found at a point that balances between the structural capacity and the seismic demand. This point is called Performance Point and in Advance Design it can be calculated according to the Eurocode 8 N2 method or the ATC-40 Capacity Spectrum Method (CSM).