Abstract- Hancılar PhD.
CORRELATIONS BETWEEN GROUND MOTION INTENSITY MEASURES AND STRUCTURAL RESPONSE PARAMETERS THROUGH NONLINEAR DYNAMIC ANALYSES
(Thesis Supervisor: Eser Çaktı)
The assessment of the structural response via nonlinear dynamic analyses requires some characterization of the correlations between ground motion intensity measures and structural response parameters. It gains more significance to understand which properties of a recorded ground motion are most strongly related to the response caused in the structure. The primary objective of this thesis is to investigate the correlations between ground motion intensity measures and structural response parameters through nonlinear dynamic analyses of multi-degree-of-freedom (MDOF) structures under real earthquake recordings.
For this purpose, a parametric investigation on reinforced concrete buildings is carried out. The building groups are five-, ten-, fifteen- and twenty-story reinforced concrete, code-conforming, regular moment-resisting frames. They are designed for different strength reduction factors, R=2, 4 and 6. Hence there are 12 buildings under consideration in total. Finite element modeling of the buildings is achieved by using line elements inOpenSees v2.0 (UC Berkeley, 2008) environment. The line elements are composed of fiber sections and utilize the distributed plasticity approach for columns and concentrated plasticity approach for beams.
Totally 8,808 nonlinear time-domain analyses are performed. The input ground motion dataset consist of 734 horizontal components of earthquake accelerograms whose magnitudes (Mw) and source-to-site distances (RJB) vary between 5.5-7.62 and 0-100 km respectively. The recordings come from different soil conditions with the NEHRP site classes (B, C, D and E) based on the Vs,30 values and faulting mechanisms (strike-slip, normal, reverse, reverse oblique and normal oblique). As the ground motion intensity measures (IM), peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), spectral acceleration (Sa(T1)), spectral velocity (Sv(T1)) spectral displacement (Sd(T1)), Arias intensity (AI) and cumulative absolute velocity (CAV) are considered. The relative joint (one joint at each floor) accelerations and displacements as well as the plastic end rotations of beams at each floor are tracked in the nonlinear dynamic analyses. As the engineering demand parameters (EDP), maximum floor displacements (MFD), maximum inter-story drift ratios (MIDR), maximum plastic end rotations of beams (MPR) and maximum floor accelerations (MFA) are considered.
The best correlations between ground motion and structural response parameters are provided and the functions to predict the structural response via ground motion intensity measure are computed. This is done by non-parametric statistical approach, i.e. regression analysis. Then a parametric statistical evaluation procedure based on a log-normal distribution assumption is applied to the best correlations and median prediction functions are obtained. In order to make a cross-check, the prediction functions resulting from non-parametric evaluation are compared to the median prediction functions obtained from the parametric method. In addition, examples of three-dimensional structural response surfaces are provided in order to utilize in damage assessment of the buildings with similar characteristics.
The findings and observations should prudently be utilized in selection and scaling/modification of ground motion recordings as input for the nonlinear dynamic analyses. The provided correlations might also help in developing better intensity measures that sufficiently and efficiently incorporate the seismic hazard at the site and that also reduce the scatter in the nonlinear structural response when using a smaller number of records.