r - The Hong Kong Polytechnic University

Experimental Program
This experiment includes both structural experiment and geotechnical experiment. This paper will focus on the
structural experiment that related to the cyclic loading test on the bridge column P2 to P4, and pseudo-dynamic
test performed on the bridge columns P2, as shown in Fig. 8. P3 column represents the benchmark pier standing
on a caisson foundation, while P4 column is similar but dealing with scouring issue on the caisson foundation
with 4m exposed length from the bottom of the column base. The bridge column is 180cm in diameter and
1030cm in height, reinforced with 30-D32 longitudinal reinforcing bars and were transversely reinforced with
D16 perimeter hoops spaced 20 cm apart, shown in Fig.9. Similar to P3 and P4, P2 column is expected to
observe the cyclic behaviour but designated to conduct pseudo-dynamic test in a pre-determined ground
acceleration first, and then pushed in a single cycle to compare the hysteresis curve obtained in P3 and P4. This
input ground motion for P2 column is a code-compatible artificial acceleration to simulate an earthquake event
of 475 year return period, and the peak ground motion given is 0.32g, based on the Specification of Seismic
Design for Bridge Structure(2009 version). Considering the biggest seismic hazard to the Niudou bridge in
decades, records at strong motion station ILA025 in March 31, 2002 is selected. The peak ground motion for
N-S and E-W directions are 118.62gal and 90.8 gal, respectively. Fortunately, this station is the closest station
can be found. As for the loading system, this experiment use wall-type piers and two supplement A-shape
reaction frames as a reaction wall, and employ two oil jacks (Fig. 7) to apply lateral force to the circular piers to
the target displacement as shown in Fig. 10 and table 5. This will enable seismic resistance performance curves
to be obtained for bridge piers with circular cross-sections.
(a) P2 column (b) P3 column (c) P4 column (d) test setup
Figure 8 Niudou bridge column specimen and test setup
(c) longitudinal reinforcement
(d) lateral reinforcement
(a) column
(b) caisson foundation
Figure 9 Dimension and arrangement of reinforcement of the column and caisson
60
Displacement(cm)
40
20
0
-20
-40
-60
0 2 4 6 8 10 12 14 16
Cycle No.
Figure 10 Displacement-control
loading protocol
Drift
ratio
(%)
Target
Disp.
(cm)
Table 5 Target drift ratio and displacement for cyclic loading test
0.25 0.375 0.5 0.75 1.0 1.5 2.0 3.0 5.0
2.575 3.86 5.15 7.73 10.3 15.45 20.6 30.9 51.5
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