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

The main bridge from Bent 1 to Pier 4 includes one main span and two side spans of thecable-stayed structure. It is separated from the Illinois approach by an expansion joint ontop of Pier 4. At the expansion joints, the main bridge and the Illinois approach have thesame displacement in the transverse direction but independent longitudinal moment,resulting in a relatively weak connection between two parts. Those channels in Table 3.1,which are located on the main bridge, are re-listed in Table 3.2. A total of 32 stations and67 channels are on the main bridge. Among the 32 stations, D1, D2 and D3 are located atthe top of the foundation. The records at these stations approximately represent the rockmotion of the bridge during earthquakes.Table 3.2Designation of station and channels for main bridgeStation Channels Station Channels Station Channels7405.B1 HN2 HN3 HNZ 7405.L6 HN2 HNZ 7405.R1 HNZ7405.C1 HNZ 7405.M1 HN3 7405.R2 HN2 HNZ7405.C2 HN2 HNZ 7405.M2 HN2 HN3 7405.R3 HNZ7405.D1 HN2 HN3 HNZ 7405.M3 HN3 7405.R4 HN2 HNZ7405.D2 HN2 HN3 HNZ 7405.M4 HN2 HN3 7405.R5 HNZ7405.D3 HN2 HN3 HNZ 7405.P1 HN3 7405.R6 HN2 HNZ7405.L1 HNZ 7405.P2 HN2 HN3 7405.T1 HN2 HN37405.L2 HN2 HNZ 7405.P3 HN3 7405.T2 HN2 HN37405.L3 HNZ 7405.P4 HN2 HN3 7405.T3 HN2 HN37405.L4 HN2 HNZ 7405.P5 HNZ 7405.T4 HN2 HN37405.L5 HNZ 7405.P6 HN2 HN3 HNZ Station=32; Channels= 673.3. Measured dataThe dynamic responses of the bridge induced by earthquake excitations and traffic loadscan be obtained from the seismic instrumentation system. In this section, some responsedata from the system are analyzed. Two sets of field-measured data were selected. Oneset is two minutes of traffic-induced vibration data in a time period from 19:20′40″ to19:22′40″ on July 25, 2006. Although a Richter’s Magnitude 2.2 earthquake occurred at19:35′39″ (Universal Time) on July 25, 2006, in southeastern Missouri (36.76N and89.49W), the response at the bridge site was negligible. The other set of data was inducedby an earthquake event, which occurred at 12:37′32″ on May 1, 2005 with a Richter'sMagnitude 4.1. The epicenter of the earthquake was located at four miles SSE (162 o )from Manila, Arkansas and 180 km (111 miles) from the bridge. The hypocentral depthwas estimated to be 10 km (6.2 miles). This section presents an analysis of the vertical,transverse, and longitudinal acceleration responses at the bridge deck and towers. In thefollowing section, some of the corresponding amplitude spectra at various deck and towerlocations will be presented to compare with the frequencies obtained from numericalsimulations.3.3.1. Vertical vibration of the bridge deckThe vertical accelerations induced by traffic along the length of the bridge deck areillustrated in Figure 3.2 for channels L2, L4, C2, R4, and R6 over a period of twominutes. It is clearly shown that the responses of the deck at the towers (Channels L4 andR4) are much smaller than those at other locations due to the vertical support condition19