Experiments on Large Structures - Dynamic Behavior of Concrete and Seismic Engineering - page 216

Built in 1947, the suspended Beauharnois bridge is 177m long, and crosses one
of the supply canals of an hydroelectric power station south-east of Montreal. The
bridge underwent important structure modifications after a steel orthotropic deck
slab and a mixed cable-stayed suspension system were installed. Dynamic tests were
conducted on the new structure to calibrate a finite element model capable of taking
the non-linear behavior of the cables and suspension into account.

The eastern part of the symmetric bridge deck was instrumented (Figure 6.12).
Low-frequency accelerometers were placed at each suspender cable to measure the
vertical, transverse and longitudinal responses of the bridge deck and of the east
tower, under the influence of ambient and controlled traffic loads. Displacement
transducers were placed at position 14, close to the east tower, and strain gauges
placed on the main trusses.

East Tower

West Tower

[mm]
54483

54483 176784

(a)

1 9

Accelerometers

15 16

134 kN 1 8 3 kN 41 kN

167 kN Accelerometers' reference

17 18

20

223 kN 57 kN

1 2 3 4 5 6 7 0 8

9 10 11 12 13

14

Test vehicles with axle loads West tower Measuring locations (east span)

(b) (c)

Figure 6.12. Instrumentation of the bridge and test vehicles

Two lorries and a trailer were used to cross the bridge at 75 different speeds,
according to various positions on the bridge. The data recorded during the tests as
well as the data obtained with usual traffic were used to calculate the dynamic
amplification factor, a parameter which had rarely been calculated for stay-cable and
suspension bridges.

Figure 6.13 shows the displacement versus the time, obtained thanks to LVDT
n°2 (Position 14) with one lorry crossing at a speed of 76 km/h (48 mph). The
maximum dynamic response was then derived from the measured signal, as shown
in the figure. The maximum static response was obtained by filtering the dynamic
response with a low-pass filter. The cut-off frequency and the bandwidth of the filter