Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

The seismic responses at the top (T1 and T2) and the middle (M1 and M2) of the toweron the Missouri side (Pier 2) are shown in Figure 3.8. The two accelerations at middleheight of the tower are similar in peak value and time function. At the top of the tower,however, the south side column experienced a significantly higher longitudinalacceleration than that on the north side. The result implies that significant vibrationoccurs in torsion of the tower. Compared with acceleration at the top of towers, theaccelerations in the middle height of the towers are smaller in amplitude. Because in themiddle height of the tower, the two columns at each tower are connected with a crossbeam and the stiffness in the middle are higher. The longitudinal acceleration responsesof two towers at deck level are shown in Figure 3.9. Since at the deck level, there are thecap beams that support the deck, the accelerations shown in Figure 3.9 are even smallerthan those at the middle height of the towers.(a) Top and south side of the tower at Pier 2 (b) Top and north side of the tower at Pier 3(c) Middle and south side of the tower at Pier 2 (d) Middle and north side of the tower at Pier 3Figure 3.8Longitudinal accelerations at towers under earthquakeexcitation25