Civil Engineering Association

info:
Structural response to strong earthquake ground motion cannot be accurately predicted due to
large uncertainties and the randomness of structural properties and ground motion parameters.
Consequently, excessive sophistication in structural analysis is not warranted. For the time
being, the most rational analysis and performance evaluation methods for practical
applications seem to be simplified non-linear procedures, which combine the non-linear static
(pushover) analysis of a relatively simple mathematical model and the response spectrum
approach. In recent years, a breakthrough of these procedures has been observed. They have
been implemented into the modern guidelines and codes. The paper discusses such
procedures. After a brief overview of the methods, the major attention is focused on the N2
method, which has been implemented into the recent draft of the Eurocode 8 standard. The
theoretical background of the extended version of the method, which can be applied for
asymmetric structures, is presented. The similarities and differences between different
methods, the determination of target displacement in the capacity spectrum method, the
problems related to the application of simplified methods to analysis of 3D models, the
approximations and limitations of the simplified inelastic methods, and the direct
displacement-based design are discussed. Although different methods may yield in many
cases similar results, they differ in respect to simplicity, transparency and clarity of theoretical
background. The most important difference is related to the determination of displacement
demand. The use is inelastic spectra is considered to be more appropriate than the use of
highly damped equivalent elastic spectra.

Keywords: non-linear analysis; pushover analysis; simplified non-linear methods;
displacement-based design; inelastic spectra; torsion; asymmetric structures; Eurocode 8