Simplified Nonlinear Seismic Assessment of Structures Using Approximate SDOF-IDA Curves

Abstract eng:
Simplified inelastic procedures used in seismic design and assessment combine the nonlinear static (pushover) analysis and the response spectrum approach or nonlinear dynamic analysis of a single-degree of freedom model (SDOF). One of such procedures is the N2 method which has been developed at the University of Ljubljana and implemented into the Eurocode 8 standard. The inelastic spectrum, which is prescribed by Eurocode 8 and used for the determination of the target displacement, allows only a rough bi-linear idealization of the pushover curve and assumes an unlimited ductility. In this study an attempt has been made to predict the target displacement by four-linear idealization of the pushover curve using the approximate SDOF-IDA curves. Instead of calculating the SDOF-IDA curve for particular input parameters that describe the equivalent SDOF system, a large database of SDOF-IDA curves, which correspond to uniformly distributed input parameters (i.e. periods, damping ratios, force-displacement envelopes) and different ground-motion records, was established. The prediction of the IDA curve for a specific structure can be made by combining the database of the SDOF-IDA curves with a simple approach, known as n-dimensional linear interpolation. The application of the proposed methodology is demonstrated using an example of a four-storey reinforced concrete structure. The results obtained by the simplified nonlinear seismic assessment method are compared with the results based on the IDA analysis.

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