## 3 Record Selections  
Some researchers (e.g., [54]) have expressed their concern about the use of the maximum rotated component spectrum, introduced in the ASCE/SEI Standard 7-10 [55] which may be conservative and may not be consistent with the return period of the design earthquakes in the codes. In this study the method recommended by ASCE/SEI Standard 7-05 [56] was chosen for the selection and scaling of the ground motion records. For each bridge, 22 pairs of ground motion records (e.g., 44 horizontal components) from the PEER NGA database ([[http://peer.berkeley.edu/peer_ground_motion_database](http://peer.berkeley.edu/peer_ground_motion_database)]([http://peer.berkeley.edu/peer_ground_motion_database](http://peer.berkeley.edu/peer_ground_motion_database)), accessed in March 2014) were selected. All records were selected from crustal earthquakes, since the effects of earthquake types is not the focus of this paper (e.g., effects of different earthquake types is investigated by [PERSON] et al. [57] and [PERSON] and [PERSON] [40; 53]). It is noted that the latest edition of ASCE-07 provisions [31] require the use of at least 11 records for performing time history analysis. The number of required records \begin{table}
\begin{tabular}{c c c c c} \hline  & \(\rm T_{T1}\) (sec) & \(\rm T_{T2}\) (sec) & \(\rm T_{L}\) (sec) & \(\rm T_{G}\) (sec) \\ \hline Regular bridge & 0.75 (87\%) & 0.28 (8\%) & 0.90 (\(\approx\)100\%) & 0.82 \\ Irregular bridge & 0.93 (90\%) & 0.29 (5\%) & 1.28 (\(\approx\)100\%) & 1.09 \\ \hline \end{tabular}
\end{table} 
Table 1: Modal properties of bridges including periods and (effective modal mass ratios). Figure 4: Comparison of the experimental data for the short column of the bridge B213C tested by [PERSON] et al. [51] and results from numerical analysis: (**a**) column displacement for the maximum earthquake and (**b**) cyclic response of the column. was previously 7 records in some older codes (e.g., 2005 edition of ASCE-07 [56]). In this research a larger number of records, including 22 pairs of ground motion records, were used that is much larger than that required by seismic codes. It is noted that a larger number of records were used in this study to make sure that the directivity effects can be appropriately accounted for in the analyses. A sensitivity study by the authors regarding the number of records, which will be presented later in the paper, indicates that the use of 22 records is sufficient for the purpose of this study. The records in this paper are scaled based on the provisions of ASCE-7 [56] (i.e., amplitude scaling). For this purpose, all of the records in the pool of records were first scaled to match the target spectrum at the geometric mean fundamental period of the bridge, T\({}_{\text{G}}\). The 22 records with the best matches to the target design spectrum within the period range of interest, that also satisfied the code provisions, were then selected from the pool of records. For measuring the match with the target spectrum within a range of periods the sum of the squared errors between the logarithms of the ground motion's spectrum and the target spectrum was used as recommended by [PERSON] [58]. A computer program was developed and used to measure the match between the scaled records spectra and the target spectrum within a range of periods and select the records with the closest match that satisfies the code provisions. Although the measurement of matching is not required by seismic codes, this extra step was taken for the purpose of this study to make sure that appropriate records are selected and used to investigate the differences between 2D and 3D analysis. For each bridge the records were selected so that the average SRSS spectrum of the records matches 1.3 times the design spectrum based on the ASCE-7 provisions [56]. It is noted that the application of the 1.3 factor to the design spectrum is based on the provisions of ASCE 7-05 for performing 3D nonlinear time history analysis.