ABSTRACT
Fatih Sultan Mehmet Suspension Bridge (FSM Bridge), Istanbul was subject to a demonstration involving the block travel of a large number of heavy duty trucks over the bridge around 1:30 PM on 19/09/2013 that lasted about nine minutes. A study was conducted to analyze the response of the bridge during the demonstration.
The bridge has a clear span of 1090 m and carries 2 X 4 lanes of highway traffic. FSM Bridge has a vibration monitoring system involving 10 triaxial accelerometers on the deck, 4 biaxial accelerometers at the top of each tower and 2 accelerometers at the center of bridge on the main cables. The data acquisition is made at a rate of 100 sps. Studies conducted in the past determined that the significant portion of the fundamental frequencies is between 0.07 Hz and 1.0 Hz (Apaydin, 2002; Apaydin et al., 2012; Browjohn et al., 1992a&b; Dumanoglu, 1992). Hence, the raw acceleration data is filtered by a band pass filter, 0.05–1.5 Hz.
The truck traffic on the bridge is restricted to 10:00 PM to 7:00 AM and 10:00 AM to 4:00 PM. The peak accelerations recorded at typical days during night hours for the vertical and the transversal directions are about 7.0 cm/sec2 and 1.0 cm/sec2 respectively.
From the 3 minute maximum UD displacement time histories of sensor No. 6 (near center of the span), it is concluded that no excessive displacement developed. The maximums were well below the maximums occurring at night hours (2.5 cm versus the average 4.0–4.5 cm displacement occurring at night) (Figure 1). When the bi-directional displacement plots are analyzed a slight move was observed in the NS direction. This was attributed to the stoppage of the traffic by the police on one side of the bridge causing uneven load distribution between the main cables resulting in a slight transverse shift. 3 minute maximum/minimum UD displacements of sensor No. 6 on 19 September 2013. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig98_1.tif"/>
The spectrograms of the accelerations band pass filtered to 0.01–20.0 Hz of the sensor No. 6 indicated that the traffic induced vibrations are mostly at higher frequencies (10.0–15.0 Hz) compared to the fundamental frequencies of the bridge (0.07–1.0 Hz).
The results of the analysis indicate no unusual excessive vertical as well transversal or longitudinal movements of the bridge deck. However, prior to the block travel of trucks per the decision of the police, one side (south side) being fully loaded and the other side being (north side) almost empty caused one sided loading and transversal movement of the bridge.
