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3.1.2 Investigations at Seyhan Bridge, Turkey
The Seyhan Metro Bridge is a 3-span steel structure. The total length of the railway bridge is app. 180
m (50 m + 80 m + 50 m), the height of the piers is 10m. The bridge was opened in 1999 with a
seismic protection system consisting of two non-linear passive hydraulic dampers in longitudinal
direction at each abutment, elastomeric bearings (on the piers) and unidirectional sliding pot bearings
(on the abutments, to avoid transverse relative movements between bridge deck and abutments).
The dampers are characterized by a quasi-constant force level, i.e. the response force of the damper
stays constant and is independent from the movement velocity of the damper.
The protection system was designed according to Turkish national anti seismic rules for bridge design,
considering a peak ground acceleration of 0,36 g.
However, the Bolu earthquake (Turkey, 1999) showed a peak ground acceleration of 0,8 g, which is
more than the double value of the considered design earthquake.
The goal of the investigation was to find out, how the existing seismic protection system could be
adapted to earthquakes exceeding the design earthquake.
After modelling the bridge and the protection devices, non-linear step-by-step dynamic analyses were
made to single out an appropriate semi-active protection system which is capable to adapt to a broad
spectrum of earthquakes.
end piers 1 and 4 central piers 2 and 3
£ 20-
actual semi- semi- semi- actual semi- semi- semipassive
active 1 active 2 active 3 passive active 1 active 2 active 3
Fig. 3.3: Seyhan bridge: actual passive versus different semi-active control algorithms
Regarding the graph of Fig. 3.3, it becomes clear that the replacement of the passive dampers by semiactive
devices (i.e. semi-active 3), the maximum deformations of both end piers and central piers can
be kept below the maximum design values - even in case of earthquakes much stronger than the
design earthquake.
4 CURRENT APPLICATIONS
4.1 Vibration control of a footbridge by means of a magnetorheological tuned mass damper
Tuned mass dampers (TMD) represent a powerful tool to control dynamic vibration of footbridges
caused by excitation of crossing pedestrians. For economical and esthetical reasons, these bridges
often are carried out as light weight structures with low natural frequencies and low structural
damping. To avoid any damage resulting from vandalism as well as to ensure a certain comfort for
crossing pedestrians, damping devices have to be installed.