Wind-tunnel study on the improvement of aerodynamic stability of simplified suspension-bridge girder structures was conducted with using a 1/40-scaled section model. Objective of the study is the development of an economically superior suspension bridge with 500–1,000 m center span length. The wind-tunnel test showed that an edge-girder type cross section exhibited large amplitude torsional vortex-induced vibration as well as torsional flutter at a low wind speed. Accordingly, aerodynamic countermeasures of open grating deck and triangular faring, and structural countermeasures of center stay, diagonal bracing and mass increase were tried to improve the aerodynamic stability. Finally, feasibility of the best combination to a full-scale bridge was examined by structural analysis.
type of model(hanger interval- girder number- deck type)
1SV/Hz
1AV/Hz
1ST/Hz
1AT/Hz
1
10 − 2 − I
0.229
0.172
0.413
0.309
2
10 − 3 − RC
0.226
0.169
0.412
0.314
3
10 − 3 − I
0.258
0.197
0.435
0.331
4
10 − 6 − RC
0.250
0.190
0.432
0.324
5
10 − 6 − I
0.261
0.199
0.443
0.332
6
10 − 6 − G
0.362
0.288
0.650
0.497
7
15 − 2 − I
0.233
0.189
0.414
0.339
8
15 − 3 − RC
0.229
0.185
0.409
0.337
9
15 − 3 − I
0.258
0.214
0.436
0.361
10
15 − 6 − RC
0.246
0.203
0.423
0.346
11
15 − 6 − I
0.253
0.210
0.431
0.351
12
15 − 6 − G
0.381
0.339
0.643
0.541
13
20 − 2 − I
0.242
0.175
0.428
0.322
14
20 − 3 − RC
0.239
0.171
0.415
0.317
15
20 − 3 − I
0.266
0.196
0.434
0.334
16
20 − 6 − RC
0.251
0.185
0.426
0.317
17
20 − 6 − I
0.256
0.190
0.429
0.319
18
20 − 6 − G
0.362
0.288
0.608
0.465
Tab.2
Fig.4
Fig.5
Fig.6
No.
unit weight of suspended structure (kN/m)
deck
faring (aerodynamic countermeasures)
1
62.5
grating
none
2
Faring A
3
Faring B
4
solid
none
5
Faring A
6
Faring B
7
Faring C
8
125.1
grating
none
9
Faring A
10
Faring B
11
solid
none
12
Faring A
13
Faring B
14
Faring C
15
187.6
grating
none
16
Faring A
17
Faring C
18
solid
none
19
Faring A
20
Faring C
Tab.3
proto type
model
deck width B/m
13.5
0.3375
girder height D/m
1.0
0.025
massm/(kg·m−1)
Cases 1−7
6.38 × 103
3.99
Cases 8−14
12.76 × 103
7.98
Cases 15−20
19.14 × 103
11.96
polar moment of inertiaI/(kg m2/m)
Cases 1−7
113.4 × 103
0.0443
Cases 8−14
226.8 × 103
0.0886
Cases 15−20
340.2 × 103
0.1329
natural frequency f/Hz
vertical
Cases 1−7
0.325
2.01
Cases 8−14
0.231
1.48
Cases 15−20
0.189
1.26
torsion
Cases 1−7
0.493
4.02
Cases 8−14
0.350
3.50
Cases 15−20
0.289
2.81
structural damping δ
vertical
0.02 in log. dec.
0.020 − 0.021
torsion
0.02 in log. dec.
0.010 − 0.012
Tab.4
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11
Fig.12
Fig.13
natural frequency/Hz
1ST
1AT
1ST
1AT
1ST
1AT
base model
0.412
0.336
diagonal bracing
upper bracing
0.415
0.343
middle bracing
0.415
0.361
below bracing
0.461
0.458
diagonal bracing+ stay cable
D = 6.8 cm
D = 9.6 cm
D = 11.8 cm
two stays
upper bracing
0.415
0.363
0.415
0.367
0.415
0.369
middle bracing
0.415
0.373
0.415
0.376
0.414
0.378
below bracing
0.460
0.469
0.460
0.472
0.460
0.474
four stays
upper bracing
0.417
0.377
0.417
0.384
0.416
0.387
middle bracing
0.416
0.384
0.416
0.388
0.416
0.391
below bracing
0.461
0.478
0.461
0.483
0.461
0.485
Tab.5
Fig.14
1
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