EVALUATION OF WIND RESISTANCE OF PARALLEL PC
EXTRADOSED BRIDGE(HIMIYUME OHASHI BRIDGE)
Osaka Branch (Kyushu Branch office)Tomotaka FUJITATokyo Civil Engineering Branch

Yutaka KOMURA

1. Introduction
Table-1 Specifications of the bridges

Himiyume Ohashi Bridge on the Nagasaki Expressway
consists of two extradosed bridges (Phase I and Phase II)

Length㸭Phase I: 365.0m / 91.8㸩180.0㸩91.8m

running parallel. Structurally, they are made of PC slabs

Span lengths

Phase II: 373.5m / 91.0㸩182.0㸩98.0m

with corrugated steel webs, continuously laid over threeGirder heightD = 4.05m

spans (Fig.1 and Photo.1). Considering that the bridge is

Total width

B = 12.95m(Phase I), 12.60m(Phase II)

put in unfavorable structural conditions for wind resistance,

Center-to-W = 22.9m

we evaluated the wind resistance of the bridge, taking into

center distance(Center of Pier 1 ~ Pier 2)

account the airflow characteristics at the location of theConstruction

Cantilever erection method

bridge.

methodThe wind resistance of the parallel bridges was evaluatedby confirming through a wind tunnel test that the resonant

2. Evaluation process for wind-resistance performance

amplitude of over-excitation (vibration amplitude of verticalFirst, wind velocity in a construction site of Himiyumereflection is less than the structural allowable amplitude).

Ohashi Bridge was observed in order to determine airflow

The specifications of the bridge are shown in Table-1 andconditions, attack angle and turbulent intensity for wind

Photo-1. Figure-1 shows the general drawing of the bridges.
Phase I bridge

tunnel test. Then, wind tunnel test was conducted using

100650Bridge length 365000
Girder length 364800
18000091750

4050A191750

RR

erRivkaizu
sukSu

P1

eigenvalue analysis results of whole bridge models. Finally,

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19000 27466

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fectural R
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14500

E

sectional model of girders which were design based on

100
650

safety of girders oscillation due to vortex-induced vibration
was evaluated by comparing resonance amplitude of thevibration obtained by the wind tunnel test with allowable

P2

Phase II bridge
500
750

amplitude estimated by structural analysis.

Bridge length 373500
Girder length 372500
182000

91000

98000

4050

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erRivkaizusukSu

3. Wind tunnel test

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19000 30000

E500
750

The experimental specimen was a rigid partial modelwith a length of 2.7 m and a scale of 1/18 which was cut outof the longitudinal section in the axis direction of the bridge

P2

Figure-1 Specifications of the bridges(Photo-2). Figure-2 shows relationships between the girders
and definitions of wind direction and attack angle. The

Phase II bridge in front

center-to-center distance of girders was simulated at thecenter of span between Pier 1 to Pier 2 where the verticaldeflection of girder is maximum value.
The models supported at both ends by springs were given
one degree of freedom toward vertical direction. The
structural damping (hereinafter referred to as “logarithmicdecrement”) was based on the result of vibration
examination conducted after the completion of Phase I, andwas adjusted by electromagnetic damper in the test.

Photo-1 Himiyume Ohashi Bridge

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技報 第 19 号（2021 年）

Deflection vortex-excited oscillation
resonance amplitude (cm)Phase II bridge

Phase I bridge

Photo-2 Model of wind tunnel test
Mountain winddirection
Phase Ibridge-5°

DB

allowable amplitude(fatigue)
allowable amplitude(proof stress)

FP
18.2cm21.2cm17.3cm16.6cmFP

0.1

Figure-4 Relationship between logarithmic decay rate and5°

resonance amplitude of leeward bridge (Phase I)

5. Evaluation of wind resistance9°

W

Estimation(į logarithmic decay rate į -)DB0°Wind tunnel test

100.01

Sea winddirection

Phase IIbridge

100

Figure-4 shows the relationship between the logarithmic

Figure-2 Wind directions and angles of attack for the wind

decay factor ț and the resonance amplitude of vortex

tunnel test

excitation for the leeward bridge under a turbulent flow (IuҸ8%) producing vortex excitation, with the sea side wind

4. Results of the wind tunnel test

direction and at an angle incidence of 5°. The logarithmic

As a result, the resonance amplitude of the windward

decay rate used for the wind resistance evaluation wasbridge was less than half of the single bridge. On the otherGHWHUPLQHGWREHǅ IRUWKHDFWXDO bridge vibration

hand, the resonance amplitude of the leeward bridge

measurement during the construction of the Phase I bridge.

presented a typical angle of incidence characteristic. At theThe estimated resonance amplitude was 18.2 cm, less thanangles of incidence of -5° and 5°, the amplitude was larger

24.1 cm, a calculation value from the fractural resistance atthan that of the single bridge.

the moment the tensile reinforcement stress reaches theFor the leeward bridge (Phase I bridge) with sea windallowable level.

direction/5° angle of incidence which have the largest

On the other hand, this wind tunnel test value was 18.2

resonance amplitude recorded, the dynamic response

cm, exceeding the fatigue verification amplitude 16.6 cm

characteristics

airflowwhich corresponds to 2 million vibration repetitions. Fromconditions (Figure-3). The resonance amplitude in thethe allowable number of repetitions obtainable from theuniform flow condition was 29.1 cm, while the resonancestress acting in the girder and the predicted number ofamplitude in the condition of the ͆turbulent flow͇ (Iu Ҹvibration repetitions considering the frequency of wind8%) was 21.2 cm, and a 27 % decrease from the uniform

velocities of resonance range, we calculated the cumulative

airflow was confirmed.

damage degree, which was much less than a unity.

werecomparedfor

From this result, the integrity of the structure was proved

Uniform flow

35

29.1cmin terms of both fatigue verification and wind resistance.

Turbulent(IuҸ8%)30

Converted amplitude ofreal bridge (cm)different

Verification velocity

25Key Words㸸extradosed bridge, parallel bridge,

21.2cm20

wind tunnel test, wind resistance design

1510500102030



506070

Tomotaka FUJITA

Converted velocity at real bridge (m/s)

Yutaka KOMURA

Figure-3 Dynamic response characteristics of leeward
bridge (Phase I)

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