## 6 Ground Motion Database  
Both record selection and scaling are equally important processes for successful seismic analyses of the structures. Apposite selection of the records considering the hazard conditions for a given site helps to increase accuracy by achieving better estimates of the structural actions. Before scaling ground motions, it is necessary to define the hazard conditions associated with a given site either through deterministic or probabilistic site-specific hazard analysis or alternatively using the seismic hazard maps. The parameters to be considered in identifying the scenario conditions are those that have the most influence on ground motion spectral shape, which includes the magnitude range of anticipated significant event, distance range of the site from the causative fault, site-condition (site-geology generally described by average shear-wave velocity within 30 m), and directivity  
Figure 8: CsiBridge output for the first three modes of vibration for the model RC arch bridge. (**a**) 1 st mode (Transverse & symmetric torsion); (**b**) 2 nd mode (Longitudinal); (**c**) 3 rd mode (Transverse & anti-symmetric vertical torsion). Figure 9: Mass participation vs. mode number. effect [30]. In this study, the model RC arch bridge was subjected to real world near-field and far-field ground motions extracted from the Pacific Earthquake Engineering Research (PEER) database [31]. Ground motion records from earthquakes in the magnitude (\(M_{w}\)) range of 6.00 to 7.5 within 10 km and 100 km of the causative fault plane were selected as near-field and far-field earthquakes, respectively. Relevant information from the ground motion database, including the station, magnitude, earthquake components, distance from the fault and peak ground acceleration (PGA) is presented in Tables 2 and 3. The ground motion types selected for this study were from site class D of the AASHTO [19] specification, with an average shear wave velocity for the top 30 m of soil, \(Vs_{30}\), in the range of 185 m/s to 365 m/s. The ground motion values were then scaled to have similar recorded amplitudes; hence, the average value of 5% damped response spectra for the suit of records was not less than the design response spectrum of the site for period ranging from \(0.2T\) to \(1.5T\)[32], where \(T\) is the period corresponding to the fundamental mode of the bridge. The \"matched to response spectrum\" option available in the ETABS V16.2.1 [33] software was utilized to scale the recorded ground motion values. Figure 10 shows the 5% damped response spectra for the longitudinal and transverse components of the scaled record; the design spectra recommended by AASHTO [19] and the average response spectrum are also shown for comparison. As the data presented in Figure 10 show, the scaling culminates in a geometric mean spectrum that closely matches the target spectrum over the significant range of the period for the PEER [32] methodology. The comparison of the AASHTO design spectra and the average longitudinal and transverse responses of the recorded ground motion thus provide a better understanding of the relationship between spectral amplitudes and structural period.